Some Basic Concepts of Chemistry (Chemistry ki Kuch Basic Concepts): Class 11 Chemistry Chapter 1 Hinglish mein

Chemistry Part 1 · Hinglish notes, simulations aur practice · Official NCERT chapter PDF ↗

Published 18 Oct 2026 · Updated 18 Oct 2026

107 min
1 simulation
39 practice questions
32 MCQs

Is chapter mein aap kya seekhenge

Samjhao ki chemistry kaise viksit hui, India ki lambi chemical parampara samet, aur daily life aur economy mein iski importance batao
Matter ki teen states ko particles ke roop mein samjhao aur matter ko mixtures, elements ya compounds mein classify karo
SI base units aur prefixes use karo, mass aur weight mein fark karo, density aur temperature scales ko jodo, aur dimensional analysis se units convert karo
Numbers ko scientific notation mein likho, significant figures aur rounding ke rules lagao, aur precision aur accuracy mein fark karo
Chemical combination ke paanch laws batao aur lagao, aur unhe Dalton ki atomic theory aur Avogadro ke law se samjhao
Atomic, average atomic, molecular aur formula masses calculate karo aur mole, molar mass aur Avogadro constant ka use karo
Composition data se mass percentages, empirical formulas aur molecular formulas nikalo
Stoichiometric calculations karo, jismein limiting reagents aur concentration ko mass per cent, mole fraction, molarity aur molality ke roop mein nikalna shaamil hai

NCERT Chemistry Class 11, Chapter 1, pp. 1–28 par based original companion text. Yeh NCERT se juda nahi hai aur NCERT ne ise endorse nahi kiya hai.

Dosa batter ko raat bhar bahar chhod do, subah tak woh phool jaata hai aur khatta ho jaata hai. Monsoon bhar bahar pade iron gate par bhoori, papdi jaisi parat jam jaati hai. Paper bag mein band hara aam naram aur meetha ho jaata hai. Har case mein substances khud badalkar naye substances ban gaye hain. Chemistry (रसायन विज्ञान) yeh poochti hai ki substances kis cheez se bane hain, unke particles kaise arranged hain, woh kaise behave karte hain aur doosre substances mein kaise badalte hain.

Yeh unit poore course ke liye toolkit taiyaar karta hai. Hum matter ko types mein baantenge, quantities ko naapna aur unhe imaandaari se report karna seekhenge, un laws se milenge jinhone scientists ko yakeen dilaya ki atoms sach mein hote hain, aur mole ki madad se atoms ko tolkar ginna seekhenge. Unit ke end tak tum predict kar paoge ki ek reaction kitna product de sakta hai, aur yeh skill tum lagbhag har agle chapter mein use karoge.

Chemistry ka Vikas

Ek organised, naap-tol karne wali science ke roop mein chemistry sirf lagbhag teen sau saal purani hai, lekin log ise usse kaafi pehle se karte aa rahe the. Medieval alchemists do aise inaamon ke peeche bhaage jo kabhi exist hi nahi karte the: ek philosopher's stone (पारस, paras) jo iron ya copper ko gold bana de, aur ek elixir of life. Lagbhag 1300 se 1600 CE tak kai log medicines ki taraf mude, is phase ko iatrochemistry kehte hain. Yeh khojein fail ho gayin, lekin apne peeche asli skills chhod gayin: distilling, crystallising, purifying aur weighing. Arab scholars is kala ko Europe le gaye, jahan eighteenth century mein chemistry ek quantitative science ban gayi.

China aur India ki apni alchemical paramparayein thin. Sanskrit texts is subject ko Rasayana Shastra kehte hain; ismein metallurgy, medicine, dyes, glass aur cosmetics shaamil the. Timeline kuch aisi Indian uplabdhiyan dikhati hai jinke liye achhe saboot hain.

Timeline

Yugon se India mein chemistry

c. 2600–1900 BCE
Harappa ke crafts
Bhatti mein pakki eenten, glazed faience beads aur tin ya arsenic se sakht kiya gaya copper: yeh sab controlled heating ke products hain.
BCE (dates par bahas hai)
Kanada ka paramanu
Kanada ke Vaisheshika school ne sikhaya ki substances chhote, hamesha rehne wale particles, paramanu, se bante hain, jo jodiyon aur teen-teen ke groups mein jud sakte hain.
Lagbhag 300 BCE se
Wootz steel
South India ke lohar sealed clay crucibles mein high-carbon wootz steel banate the; iska vyapar door pashchim tak hota tha.
CE ki shuruaati sadiyan
Ayurvedic chemistry
Charaka aur Sushruta Samhitas caustic alkalis (kshara) aur bhasmas ka varnan karti hain, yaani baar-baar garam karke banaye gaye metal powders.
c. 400 CE
Delhi ka iron pillar
7 m se zyada uncha ek wrought-iron pillar lagbhag solah sadiyon se khule mein khada hai aur us par bahut kam rust laga hai.
6th sadi CE
Brihat Samhita
Varahamihira ka encyclopaedia perfumes ke recipes deta hai, aur ubale hue plant extracts aur resins se ek sakht plaster (vajralepa) banane ka tareeka bhi.
Shuruaati medieval kaal
Rasaratnakara
Nagarjuna ke naam se jaana jaane wala ek granth mercury compounds aur copper, silver aur gold nikalne ka varnan karta hai.
Medieval kaal
Zawar mein zinc
Zawar, Rajasthan ke retorts dikhate hain ki yahan zinc ko distil kiya jaata tha, Europe mein yeh method use hone se sadiyon pehle.
1892
Bengal Chemicals
Acharya Prafulla Chandra Ray ne Kolkata mein medicines aur chemicals banana shuru kiya, aur India ki pehli modern chemical industries mein se ek ki neev rakhi.

Inmein se kuch ideas hairaan karne wale tarike se modern lagte hain. Metals ko peeskar aur garam karke bahut baareek bhasma powders banane se unka behaviour badal jaata hai, aur kuch bhasmas ki studies mein sirf kuch das nanometre ke particles mile hain, jo aaj ki nanotechnology wali size range hai. Kanada ka paramanu, jo John Dalton ki 1808 ki atomic theory se kai sadiyon pehle diya gaya tha, is baat ka sabse saaf shuruaati Indian bayan hai ki matter particles se bana hai. Eighteenth century se imported goods aur colonial rule ki wajah se kai desi techniques khatam hone lagin, aur modern laboratory chemistry Indian colleges tak sirf late nineteenth century mein pahunchi.

In paramparaon mein kami thi Kanada ke soche hue particles ko ginne ke tareeke ki. Is unit ke end se pehle tum bata paoge ki ek paracetamol tablet mein kitne molecules hote hain.

Quick check

2 mein se 1

Kaun sa description iatrochemistry par fit baithta hai?

Alchemy jiska lakshya base metals ko gold mein badalna thaChemistry jo mainly medicines banane mein lagayi gayiEighteenth-century Europe ki modern chemistryOres se nikale gaye metals ki study

Answer dekho

Answer (B) Chemistry jo mainly medicines banane mein lagayi gayi

Iatrochemists (lagbhag 1300–1600 CE) ne alchemy ko medicines ki taraf moda. Gold banana alchemy ki purani khoj thi.

1.1 Chemistry ki Importance

Chemistry ko aksar central science kaha jaata hai: yeh physics se laws udhaar leti hai aur biology, geology, medicine aur engineering ko explanations deti hai. Upar ki ozone, nerve mein daudta signal aur tumhare phone ki silicon chip, sab mein chemistry kaam kar rahi hai.

Food. Urea jaise fertilisers India ki zyadatar fasalon ko poshan dete hain; 2015 se India ka saara urea neem-coated hai taaki uski nitrogen dheere-dheere release ho. Pesticides, preservatives aur packaging bhi chemists ki den hain.
Health. Chemists paracetamol se lekar anti-cancer drugs tak medicines design karte hain, banate hain aur purify karte hain. Oral rehydration solution, yaani glucose aur salts ka ek balanced mix, ne diarrhoea se peedit laakhon bachchon ki jaan bachayi hai.
Materials. Polymers, optical fibres, lithium-ion batteries, superconducting ceramics aur conducting plastics, yeh sab aise substances design karne se aaye jinki electrical, magnetic ya optical properties hum chunte hain.
Environment. Chemists ne un CFCs ko replace kiya jo ozone layer ko patla kar rahe the, aur ab ozone layer dheere-dheere theek ho rahi hai. Carbon dioxide aur methane jaisi greenhouse gases ko manage karna ek bada khula problem hai.
Economy. Acids, alkalis, fertilisers, dyes, cement, polymers, metals aur medicines banane wali industries mein laakhon log kaam karte hain.

Challenges abhi baaki hain, living cells ki chemistry se lekar solar energy ko store karne aur waste ko resources mein badalne tak. Yeh saara kaam is unit ke basic ideas par tika hai, aur shuruaat hoti hai is sawaal se ki matter kya hai.

Quick check

Inmein se kaunsi uplabdhiyan mainly chemistry ki hain? Jo bhi sahi hon, sab chuno.

Ozone ko nuksaan pahunchane wale CFCs ke substitutesNeem-coated urea jo nitrogen dheere-dheere release karta haiMoon tak ki distance naapnaLithium-ion batteries

Saare sahi options chuno

Answer dekho

Answer

(A) Ozone ko nuksaan pahunchane wale CFCs ke substitutes
(B) Neem-coated urea jo nitrogen dheere-dheere release karta hai
(D) Lithium-ion batteries

CFC substitutes, coated fertilisers aur battery materials, sab naye substances design karne par nirbhar hain. Moon ki distance naapna physics aur astronomy hai.

1.2 Matter ka Nature

Ek kankad, football ke andar ki hawa, matke ka paani aur tumhara apna body, in sab mein do baatein common hain: har ek ka mass hai, aur har ek jagah gherta hai. Jis cheez mein yeh dono properties hon, woh matter (द्रव्य) hai. Light, heat aur sound matter nahi hain; yeh energy ke forms hain.

1.2.1 Matter ki States

Koi sample solid hai, liquid hai ya gas, yeh is par depend karta hai ki uske particles kitni doori par hain aur kitni azaadi se move karte hain. Ek regular pattern mein bandhe hue aur sirf apni jagah par hilte hue: yeh solid hai. Ab bhi ek doosre ko chhoote hue, lekin ek doosre ke paas se phisalne ke liye free: liquid. Door-door faile hue aur random tarike se tezi se bhaagte hue: gas.

Table 1.1Particle arrangement kaise shape aur volume tay karta haiNCERT Fig. 1.1 · p. 4

	Particles	Shape	Volume
Solid	kase hue, ordered, apni jagah par vibrate karte hain	fixed	fixed
Liquid	paas-paas, lekin ek doosre ke paas se phisalte hain	container ka shape le leta hai	fixed
Gas	door-door, tez, random	container ko bhar deti hai	container ko bhar deti hai

Temperature ya pressure badalne se ek state doosri state mein badal jaati hai. Ice ko garam karo to woh pighal jaati hai; paani ko garam karo to woh ubalta hai; steam ko thanda karo to steps ulti disha mein chalte hain. Pressure bhi matter karta hai: LPG khuli hawa mein gas hai lekin cylinder ke andar dabakar liquid bana di jaati hai, isiliye bhara cylinder hilane par chhalakne ki awaaz aati hai.

SimulationPaani ki teen states mein particles

Paani ke particles ka ek band box, saath mein ek thermometer aur minus 20 se 120 degrees Celsius tak ka temperature slider. 0 degrees se neeche particles ek regular pattern mein baithe rehte hain aur sirf vibrate karte hain; 0 aur 100 degrees ke beech woh paas-paas rehte hain lekin neeche ek doosre ke paas se move karte hain; 100 degrees se upar woh tezi se poore box mein phail jaate hain. Ek label state ka naam batata hai.

Fig. 1.1Ek band box mein paani ke particles. Play dabao, phir temperature slider ko ice se steam tak le jao.

Try karo

$- 10^{\circ} C$ se shuru karo aur Play dabao. Kya particles apni jagah badalte hain, ya sirf hilte hain?
Box ko $50^{\circ} C$ tak garam karo. Kya badalta hai: sample ka shape ya uska volume?
$100^{\circ} C$ se upar jao. Gas poore box ko kyun bhar deti hai?

1.2.2 Matter ka Classification

Bulk matter ko teen sawaalon se sort kiya ja sakta hai (Fig. 1.2). Pehla: kya koi physical method, jaise sieving, filtering, magnet, evaporation ya distillation, ise simpler parts mein alag kar sakta hai? Agar haan, to yeh mixture (मिश्रण) hai; agar nahi, to yeh pure substance hai.

4/4Reaction mein toot jaata hai: compound; toda nahi ja sakta: element.

Fig. 1.2Teen haan-ya-nahi wale sawaal matter ke kisi bhi sample ko chaar kinds mein sort kar dete hain.NCERT Fig. 1.2 · p. 5

Ek decision chart jo step by step badhta hai. Step 1: Matter label wala ek box, saath mein sawaal 'Physically alag ho?'. Step 2: yes se Mixture, no se Pure substance. Step 3: Mixture ke neeche, 'Same all through?' se Homogeneous (brine, air) ya Heterogeneous (ret aur paani), har ek ke saath particle sketch. Step 4: Pure substance ke neeche, 'Chemically toot-ta?' se Compound (water, salt) ya Element (copper, oxygen).

Definition

Mixture

Do ya zyada pure substances kisi bhi proportion mein mile hue, har ek apni properties rakhta hai; physical methods se alag kiye ja sakte hain.

ExampleBrass, sea water, mitti wala paani.

Mixture ke substances uske components hote hain, aur unke proportions tumhari marzi par hain: nimbu-paani ko apni marzi se zyada meetha ya zyada khatta banaya ja sakta hai. Agar components particles ke level tak barabar faile hon, yaani upar ka ek ghoont neeche ke ghoont jaisa hi lage, to mixture homogeneous hai, jaise brass, vinegar ya achhe se ghola hua nimbu-paani. Agar banawat ek hisse se doosre hisse mein badalti hai, aksar dikhne wale tukdon ke saath, to yeh heterogeneous hai, jaise mitti wala paani, fruit salad ya sulfur powder mein mile iron filings. Physical methods mixtures ko alag kar dete hain: magnet iron filings ko utha leta hai, filter mitti ko rok leta hai aur evaporation sea water se salt ko peeche chhod deta hai.

Pure substance ki composition fixed hoti hai aur har sample mein properties same hoti hain, jaise distilled water, copper, sucrose ya baking soda. Ganne se mile sucrose aur sugar beet se mile sucrose, dono mein carbon, hydrogen aur oxygen mass ke hisaab se bilkul same proportions mein hote hain, aur koi bhi filtering ya evaporation un elements ko alag nahi kar sakta.

Pure substances do kinds ke hote hain. Element (तत्व) mein sirf ek kind ka atom hota hai. Uske atoms akele reh sakte hain, jaise helium ya iron ke tukde mein, ya milkar molecules bana sakte hain, jaise do-atom wali chlorine, teen-atom wali ozone ya aath-atom wala sulfur (Fig. 1.3). Compound (यौगिक) tab banta hai jab alag-alag elements chemically judte hain, hamesha mass ke hisaab se same proportion mein; unhe dobara alag karne ke liye chemical reaction chahiye.

5/5Ek kind ka atom, fixed combinations, ya substances ka ghaal-mel.

Fig. 1.3Elements mein ek hi kind ka atom hota hai, akela ya molecules mein; compound mein alag-alag atoms ke ek jaise molecules hote hain; mixture mein alag-alag substances saath-saath rehte hain.NCERT Fig. 1.3, 1.4 · p. 6

Chaar particle panels ek key ke saath (N medium circle, O chhota circle, H aur chhota circle, Ar bada dashed circle). Step 1 'Element: argon' ko highlight karta hai, ek jaise akele atoms. Step 2 'Element: oxygen' ko highlight karta hai, ek jaise do-atom wale molecules. Step 3 'Compound: ammonia' ko highlight karta hai, ek nitrogen aur teen hydrogen atoms wale ek jaise molecules. Step 4 'Mixture: air' ko highlight karta hai, nitrogen ke jode, ek oxygen ka joda aur ek argon atom aapas mein ghule-mile. Step 5 chaaron ko dikhata hai.

Definition

Element

Sirf ek kind ke atom se bana pure substance; chemical reactions ise simpler substances mein nahi tod sakte.

ExampleCopper ( $C u$ ), oxygen ( $O_{2}$ ), sulfur ( $S_{8}$ ).

Definition

Compound

Do ya zyada elements se bana pure substance jo mass ke hisaab se fixed ratio mein chemically jude hon, aur jiski properties uske elements se alag hon.

ExampleWater ( $H_{2} O$ ), ammonia ( $N H_{3}$ ).

Compound sach mein ek naya substance hota hai. Sodium ek naram metal hai jo paani ke saath zor se react karta hai aur chlorine ek zehreeli hari gas hai, phir bhi dono milkar table salt banate hain. Compound ki properties uske elements ki properties ka average nahi hoti.

1.3 Matter ki Properties aur unka Measurement

Har substance ki kuch properties hoti hain jo use pehchaanti hain, bilkul waise hi jaise fingerprint kisi insaan ko pehchaanta hai. Science mein unhe use karne ke liye humein unhe observe karna hota hai aur jahan tak ho sake, measure karna hota hai.

1.3.1 Physical aur Chemical Properties

Ice pighalne ke baad bhi tumhare paas paani hi rehta hai, isliye melting point ek physical property hai: ise tum tab observe kar sakte ho jab substance apni pehchaan banaye rakhta hai. Jalne se paper raakh aur gases mein badal jaata hai, isliye flammability, jo tabhi dikhti hai jab substance naye substances mein badalta hai, ek chemical property hai. Chaandi ki payal mein dono kinds hain: uski chamak aur density physical hain, jabki hawa mein uska dheere-dheere kaala padna, jab silver sulfur compounds ki thodi si matra se react karta hai, chemical hai.

Compare

Property ke do kinds

Physical

Substance ko badle bina observe ki jaati hai
Rang, smell, melting aur boiling points, density, solubility, hardness

Chemical

Sirf chemical change ke through observe hoti hai
Jalna, acids ya bases ke saath reaction, rusting, tarnishing

Chemists dono kinds ka use karke substances ke behaviour ko describe, explain aur predict karte hain. Is section ka baaki hissa physical properties ko measure karne ke baare mein hai.

1.3.2 Physical Properties ka Measurement

Yeh kehna ki darwaaza '2.1 lamba' hai, kisi ko kuch nahi batata; ' $2.1 m$ ' sabko batata hai. Measured quantity hamesha ek number aur uske saath unit hoti hai, number batata hai ki us unit ke kitne hisse usmein fit hote hain.

Tumhare dada-dadi ko yaad ho sakta hai ki ghee ser ke hisaab se aur gold tola ke hisaab se khareeda jaata tha; India ne 1958 mein metric units apnana shuru kiya. Metric system, jo 1790s mein France mein bana, das ki powers mein upar-neeche jaata hai, isliye conversions aasaan hain, Britain ke inches, feet aur pounds wale English system ke ulat. Science ko isse zyada chahiye tha: ek aisa system jis par har desh sehmat ho.

1.3.3 International System of Units (SI)

Saat base quantities, har ek ki ek base unit ke saath, International System of Units ka core banati hain, jise iske French naam Le Système International d'Unités se SI kehte hain; speed, volume, density aur baaki har quantity inhi se derived hoti hai. SI ko 1960 mein General Conference on Weights and Measures (CGPM) ki 11th meeting mein apnaya gaya, yeh woh body hai jo Metre Convention ke peeche hai, ek treaty jo 1875 mein Paris mein sign hui thi.

Table 1.2Saat SI base quantitiesNCERT Table 1.1 · p. 7

Base quantity	Symbol	SI unit	Unit symbol	Chemists ise kahan dekhte hain
length	$l$	metre	m	bond lengths
mass	$m$	kilogram	kg	reactants ko tolna
time	$t$	second	s	reaction rates
electric current	$I$	ampere	A	electrolysis
thermodynamic temperature	$T$	kelvin	K	garam aur thanda karna
amount of substance	$n$	mole	mol	particles ginna
luminous intensity	$I_{v}$	candela	cd	light ke sources

20 May 2019 se har base unit ko nature ke ek constant ko exact value dekar fix kiya gaya hai, taaki unit ko kisi bhi achhe se equipped laboratory mein dobara banaya ja sake: second ko caesium-133 atom ki ek frequency se, metre ko light ki speed se, kilogram ko Planck constant se, aur isi tarah baaki.

Table 1.3Har base unit ke peeche ka constant (2019 se exact)NCERT Table 1.2 · p. 8

Unit	Fixed constant	Exact value
second	caesium frequency $Δ ν_{C s}$	$9 192 631 770 H z$
metre	light ki speed $c$	$299 792 458 m s^{- 1}$
kilogram	Planck constant $h$	$6.62607015 \times 10^{- 34} J s$
ampere	elementary charge $e$	$1.602176634 \times 10^{- 19} C$
kelvin	Boltzmann constant $k$	$1.380649 \times 10^{- 23} J K^{- 1}$
mole	Avogadro constant $N_{A}$	$6.02214076 \times 10^{23} m o l^{- 1}$
candela	luminous efficacy $K_{c d}$	$683 l m W^{- 1}$

Prefixes SI units ko das ki powers se chhota-bada karte hain, taaki humein zeros ki lambi line na likhni pade: carbon–carbon bond lagbhag $154 p m$ lamba hota hai aur ek tablet mein $500 m g$ medicine ho sakti hai.

Table 1.4Aam SI prefixesNCERT Table 1.3 · p. 9

Prefix	Symbol	Factor	Example
femto	f	$10^{- 15}$	ek bond ~ $10 f s$ mein vibrate karta hai
pico	p	$10^{- 12}$	atomic radii ~ $100 p m$
nano	n	$10^{- 9}$	visible light $400$ – $700 n m$
micro	µ	$10^{- 6}$	ek baal ~ $70 μ m$ mota
milli	m	$10^{- 3}$	$500 m g$ ki tablet
centi	c	$10^{- 2}$	$15 c m$ ki test tube
deci	d	$10^{- 1}$	$1 d m^{3} = 1 L$
kilo	k	$10^{3}$	$14.2 k g$ ka LPG cylinder
mega	M	$10^{6}$	$2 M W$ ki wind turbine
giga	G	$10^{9}$	$1 G H z$ ka processor

Poori list yocto ( $10^{- 24}$ ) se yotta ( $10^{24}$ ) tak jaati hai, aur 2022 se quecto ( $10^{- 30}$ ) se quetta ( $10^{30}$ ) tak.

1.3.4 Mass aur Weight

$1.00 k g$ atta ka packet Moon par le jao, usmein bilkul utna hi aata rahega: uska mass, yaani usmein matter ki matra, nahi badla. Phir bhi woh tumhare haath par sirf ek-chhathe hisse jitna zor lagata hai, kyunki uska weight, yaani us par gravity ka khinchav, is par depend karta hai ki woh kahan hai: Delhi mein lagbhag $9.8 N$ , Moon par $1.6 N$ . Lab mein mass ek analytical balance se naapa jaata hai jo $0.0001 g$ tak padhta hai, aur ek glass case ke andar hota hai jo pan ko hawa ke jhonkon se bachata hai. SI unit kilogram hai, lekin lab mein matra chhoti hoti hai, isliye chemists zyadatar grams use karte hain ( $1 k g = 1000 g$ ).

1.3.5 Volume

School ki paani ki tanki mein lagbhag ek cubic metre aata hai; ek beaker mein kuch sau cubic centimetres. Dono numbers volume batate hain, yaani substance kitni jagah gherta hai, jo length cubed mein naapa jaata hai. SI unit, $m^{3}$ , bench ke kaam ke liye bahut bada hai, isliye chemists $d m^{3}$ aur $c m^{3}$ use karte hain, aur litre (L) bhi, jo SI unit nahi hai lekin uske saath accepted hai.

Volume units

\begin{array}{c} 1 m^{3} = 1000 L \\ 1 L = 1 d m^{3} \\ 1 d m^{3} = 1000 c m^{3} \\ 1 c m^{3} = 1 m L \end{array}

(1.1)

3/3 $1 c m$ ka cube $1 m L$ hai; aise hazaar cubes $1 L$ bharte hain.

Fig. 1.4Har step neeche jaane par edge 10 se aur volume 1000 se divide hota hai.NCERT Fig. 1.6 · p. 9

Step 1: 1 m edges wala ek bada cube, label: 1 cubic metre barabar 1000 litres. Step 2: uske face par das-by-das grid aur ek corner cube, jo 10 cm edges wale medium cube se juda hai, label: 1 cubic decimetre barabar 1 litre. Step 3: medium cube par grid aur ek corner cube, jo 1 cm edges wale chhote cube se juda hai, label: 1 cubic centimetre barabar 1 millilitre.

Table 1.5Laboratory mein volumes naapnaNCERT Fig. 1.7 · p. 10

Device	Sabse achha use	Aam reading
measuring cylinder	jaldi, mote taur par volumes	nearest $1 m L$ tak (100 mL size)
burette	badalta volume, boond-boond karke	har $0.1 m L$ par nishan
pipette	ek fixed volume, bilkul exact	jaise $25.00 m L$
volumetric flask	solution banana	jaise mark par $250.0 m L$

1.3.6 Density

Steel ka chammach doob kyun jaata hai jabki lakdi ka chammach tairta hai? Steel har cubic centimetre mein kahin zyada mass bharta hai: uski density zyada hai, yaani per unit volume mass:

Density

ρ = \frac{m}{V}

(1.2)

jahan

$ρ$: density
$m$: mass
$V$: volume

Chemists aamtaur par SI wale $k g m^{- 3}$ ki jagah $g c m^{- 3}$ (jo $g m L^{- 1}$ ke barabar hai) use karte hain; $1 g c m^{- 3} = 1000 k g m^{- 3}$ . Paani $1.00$ , iron $7.87$ aur gold $19.3 g c m^{- 3}$ hai: gold se bhara ek litre ka carton lagbhag $19 k g$ ka hoga. Ice ( $0.92 g c m^{- 3}$ ) ka molecular framework khula hota hai, isiliye woh tairti hai.

Try karke dekho

Displacement se density

Tumhe chahiye

ek kitchen scale
mL ke nishan wala measuring jug
ek aalu, ek patthar aur ek steel ka chammach
dhaaga

Pehle guess karo

Kis object ki density sabse zyada hogi?

AaluPattharSteel ka chammach

Object ko scale par tolo.
Measuring jug ko aadha paani se bharo aur level note karo.
Object ko dhaage se tab tak neeche utaro jab tak woh bas dhak na jaaye; naya level note karo. Level jitna badha, wahi uska volume hai.
Mass ko volume se divide karo.

Table 1.6Tumhare measurements

Object	Mass (g)	Volume (mL)	Density (g/mL)
Aalu
Patthar
Steel ka chammach

Tumhari entries apne aap save hoti hain.

1.3.7 Temperature

Ghar ke thermometer par 102 °F ka bukhaar, hospital chart par 38.9 °C aur physics lab mein 312 K, teen scales par ek hi temperature hai. Kelvin (K) SI unit hai. Celsius scale normal pressure par paani ke freezing aur boiling points ko 0 °C aur 100 °C par rakhta hai; Fahrenheit scale unhe 32 °F aur 212 °F par rakhta hai (Fig. 1.5).

Celsius se Fahrenheit

t_{F} = \frac{9}{5} t_{C} + 32

(1.3)

jahan

$t_{C}$: °C mein temperature
$t_{F}$: °F mein temperature

Celsius se kelvin

T = t_{C} + 273.15

(1.4)

jahan

$T$: K mein temperature

Ek kelvin aur ek Celsius degree ka size same hai; scales mein fark sirf is baat ka hai ki zero kahan hai. Kelvin scale ka zero, $0 K = - 273.15^{\circ} C$ , absolute zero hai, sabse kam possible temperature, isliye kelvin temperatures kabhi negative nahi hote.

2/4Freezing se boiling tak 100 K, 100 °C lekin 180 °F hai: isiliye factor $9 / 5$ aata hai.

Fig. 1.5Teen scales par same temperatures; ek Fahrenheit degree ek kelvin ka sirf 5/9 hota hai.NCERT Fig. 1.8 · p. 10

K, degrees Celsius aur degrees Fahrenheit ke liye teen number lines, scale ke hisaab se bani. Step 1 ice pighalne ko mark karta hai: 273, 0 aur 32. Step 2 paani ka ubalna jodta hai: 373, 100 aur 212, brackets dikhate hain ki gap 100 K, 100 degrees Celsius lekin 180 degrees Fahrenheit hai. Step 3 absolute zero jodta hai: 0 K, minus 273 aur minus 460. Step 4 233 K jodta hai, jahan Celsius aur Fahrenheit dono minus 40 padhte hain.

Example

Teen scales par Delhi ki garmi

May ki ek dopahar Delhi ka ek weather station $46.8^{\circ} C$ record karta hai. (a) Ise °F aur K mein likho. (b) Kis temperature par Celsius aur Fahrenheit scales same reading dete hain?

Pehle khud try karo. Phir solution ek-ek step karke kholo.

Quick check

3 mein se 1

Inmein se magnesium ki chemical property kaunsi hai?

Yeh silvery-white solid haiIski density

1.74 g c m^{- 3}

haiYeh

650^{\circ} C

par pighalta haiYeh hawa mein jalkar ek safed powder banata hai

Answer dekho

Answer (D) Yeh hawa mein jalkar ek safed powder banata hai

Jalne se magnesium, magnesium oxide mein badal jaata hai, jo ek naya substance hai. Rang, density aur melting point metal ko badle bina pata kiye ja sakte hain.

1.4 Measurement mein Uncertainty

Chemistry ka har number kisi instrument se aaya hai, ya aise numbers par bani calculation se. Teen aadatein unhe sambhalne laayak aur imaandaar rakhti hain: bahut bade aur bahut chhote numbers likhne ka ek chhota tareeka, yeh dikhane ka tareeka ki measurement kitna certain hai, aur units badalne ka ek safe tareeka.

1.4.1 Scientific Notation

Atoms aur molecules behad halke aur behad zyada sankhya mein hote hain. Paani ki ek boond ( $0.05 g$ ) mein lagbhag 1 670 000 000 000 000 000 000 molecules hote hain, aur ek carbon atom ka mass lagbhag 0.000 000 000 000 000 000 000 019 9 grams hota hai. Aise numbers ko digit by digit sambhalne mein galtiyan hona tay hai.

Scientific notation ek number ko $N \times 10^{n}$ ke roop mein likhta hai, jahan digit term $N$ ke liye $1 \leq N < 10$ hai aur exponent $n$ ek whole number hai. Upar ke do numbers $1.67 \times 10^{21}$ aur $1.99 \times 10^{- 23} g$ ban jaate hain. Decimal point ko $k$ jagah left khiskane se exponent mein $k$ judta hai; right khiskane se $k$ ghatta hai: $45 600 = 4.56 \times 10^{4}$ aur $0.000 093 = 9.3 \times 10^{- 5}$ .

Multiply ya divide karna: digit terms ko multiply ya divide karo aur exponents ko jodo ya ghatao; phir adjust karo taaki $1 \leq N < 10$ rahe.
Jodna ya ghatana: pehle numbers ko same exponent ke saath dobara likho, phir digit terms ko jodo ya ghatao.

Example

Scientific notation mein arithmetic

Nikalo (a) $(4.8 \times 10^{6}) \times (3.5 \times 10^{- 3})$ , (b) $(7.2 \times 10^{5}) \div (2.4 \times 10^{- 3})$ aur (c) $(5.1 \times 10^{- 3}) - (8.7 \times 10^{- 4})$ .

Pehle khud try karo. Phir solution ek-ek step karke kholo.

1.4.2 Significant Figures

Koi bhi measurement perfect nahi hota: instrument ka scale limited hota hai aur padhne wale ki skill bhi limited hoti hai. Kitchen scale dal ke ek bag ko $0.50 k g$ dikha sakta hai, jabki laboratory balance usi bag ke liye zyada digits deta hai. Jo digits hum likhte hain, woh dikhate hain ki hum ek number par kitna bharosa karte hain.

Kisi measurement ke significant figures (सार्थक अंक) woh saare digits hain jo pakke pata hain, plus ek aakhri, andaaze wala digit. $24.36 m L$ likhne ka matlab hai ki $24.3$ certain hai aur $6$ sabse achha andaaza hai. Jab tak kuch aur na bataya jaaye, padhne wale maante hain ki aakhri digit dono taraf ek unit tak uncertain hai. Fig. 1.6 dikhata hai ki andaaze wala digit kahan se aata hai.

4/4 $12.36 m L$ likho: chaar significant figures, aakhri wala andaaze se.

Fig. 1.6Meniscus ka neeche wala hissa aankh ke level par padho. Nishan certain digits dete hain; aakhri digit do nishanon ke beech ka andaaza hai.NCERT p. 12

12 se 13 mL tak 0.1 mL ke steps wala ek bada kiya gaya burette scale, saath mein curved liquid surface aur ek dashed eye-level line. Step 1 scale dikhata hai. Step 2 12.3 aur 12.4 ke beech ke gap ko shade karta hai aur 'certain: 12.3' label lagata hai. Step 3 meniscus ki taraf ishara karta hai aur 'andaaza: 6' label lagata hai. Step 4 12.36 mL likhta hai, 1, 2 aur 3 ko certain dikhane ke liye underline karta hai aur 6 ko dashed line se estimated dikhata hai, aur 4 significant figures batata hai.

Kisi aur ke likhe number mein significant figures ginne ke liye:

Har non-zero digit ginti mein aata hai: $4.71$ mein teen hain.
Pehle non-zero digit se pehle ke zeros sirf decimal point ki jagah batate hain aur ginti mein nahi aate: $0.0082$ mein do hain.
Non-zero digits ke beech ke zeros ginti mein aate hain: $30.05$ mein chaar hain.
Aakhir ke zeros tab ginte hain jab decimal point ho: $2.500$ mein chaar, $70.0$ mein teen. Decimal point ke bina woh nahi ginte: $7000$ mein ek hai. Zyada dikhane ke liye scientific notation use karo: $7.0 \times 10^{3}$ mein do, $7.00 \times 10^{3}$ mein teen.
Exact numbers, jaise ginti (ek team mein 11 players) aur defined relations ( $1 m = 100 c m$ ), mein unlimited significant figures hote hain.
Scientific notation mein $N$ ka har digit ginti mein aata hai: $6.020 \times 10^{23}$ mein chaar hain.

InteractiveSignificant-figure checker

Fig. 1.7Ek measured number type karo. Checker har digit ko mark karta hai, rule ka naam batata hai, number ko scientific notation mein likhta hai aur is section ke tareeke se round karta hai.

Sirf dhyaan se likhe digits kaafi nahi; results bharose laayak bhi hone chahiye. Precision (परिशुद्धता) yeh hai ki baar-baar ke measurements aapas mein kitna milte hain. Accuracy (यथार्थता) yeh hai ki result true value ke kitna kareeb hai. Jis balance ko kabhi zero nahi kiya gaya, woh bahut precise readings de sakta hai jo sab same amount se galat hon (Fig. 1.8).

4/4True value par paas-paas: precise aur accurate.

Fig. 1.8Teen students ek hi 5.00 g standard ko chaar baar tolte hain. Paas-paas hona precision dikhata hai; dashed line ke kareeb hona accuracy dikhata hai.NCERT Table 1.4 · p. 13

4.80 se 5.20 g tak ek number line, true value 5.00 g par ek dashed line ke saath. Step 1 sirf yahi dikhata hai. Step 2 Meera ki readings circles ke roop mein jodta hai, 4.86 g ke aas-paas jamaa: precise, accurate nahi. Step 3 Arjun ki readings squares ke roop mein jodta hai, 4.92 se 5.11 g tak bikhri hui: precise nahi, haalaanki unka mean true value ke kareeb hai. Step 4 Kabir ki readings diamonds ke roop mein jodta hai, 4.99 aur 5.01 g ke beech jamaa: precise aur accurate.

Calculated answer usmein lage sabse kam certain measurement se zyada certain nahi ho sakta:

Jodna ya ghatana: utni hi decimal places rakho jitni sabse kam decimal places wale measurement mein hain.
Multiply ya divide karna: utne hi significant figures rakho jitne sabse kam significant figures wale measurement mein hain.

Round karne ke liye, pehla digit dekho jo tum hata rahe ho. 5 se zyada: aakhri rakhe digit ko ek badhao ( $3.476 \to 3.48$ ). 5 se kam: use waisa hi chhod do ( $2.843 \to 2.84$ ). Bilkul 5 aur uske baad sirf zeros: aakhri rakhe digit ko even banao ( $7.45 \to 7.4$ , $7.55 \to 7.6$ ), taaki rounding errors ek hi direction mein jama na hon. Agar 5 ke baad non-zero digits hon, jaise $2.451$ mein, to upar round karo ( $2.5$ ).

ExampleNCERT p. 13

Calculated result report karna

Har result sahi tarike se report karo: (a) $24.6 g + 3.218 g + 0.0952 g$ ; (b) $4.56 c m \times 1.4 c m$ ; (c) 7 ek jaise coins ka mean mass, jinka kul weight $15.0 g$ hai.

Pehle khud try karo. Phir solution ek-ek step karke kholo.

1.4.3 Dimensional Analysis

Factor-label method (jise unit factor method ya dimensional analysis bhi kehte hain) units ko safe tarike se badalta hai. $1 y d = 0.9144 m$ (exact) jaise ek relation se shuru karo. Ek side ko doosri side se divide karne par ek unit factor milta hai, yaani ek fraction jo ek ke barabar hai:

Unit factors

\begin{array}{c} \frac{0.9144 m}{1 y d} = 1 \\ \frac{1 y d}{0.9144 m} = 1 \end{array}

(1.5)

1 se multiply karne par koi quantity kabhi nahi badalti. Woh factor chuno jiske denominator mein na chahiye wali unit ho, taaki woh cancel ho jaaye, aur upar chahiye wali unit ho. Units algebraic symbols ki tarah cancel, multiply aur square ya cube ho sakti hain, aur kai factors ek hi line mein chain kiye ja sakte hain.

ExampleNCERT 1.4.3 ke examples · p. 14

Unit factors se teen conversions

Convert karo (a) cricket pitch ki $22 y d$ length ko metres mein, (b) mercury ki density, $13.6 g c m^{- 3}$ , ko $k g m^{- 3}$ mein aur (c) $72 k m h^{- 1}$ ki highway speed ko $m s^{- 1}$ mein.

Pehle khud try karo. Phir solution ek-ek step karke kholo.

Quick check

3 mein se 1

0.04060 g

mein kitne significant figures hain?

Answer dekho

Answer 4

Shuru ke zeros sirf decimal point ki jagah batate hain. 4 aur 6 ke beech ka zero ginti mein aata hai, aur decimal point ke baad aakhri zero bhi: chaar.

1.5 Chemical Combinations ke Laws

Late eighteenth century mein chemists ne reactions mein jaane wale aur bahar aane wale padarthon ko tolna, aur gas volumes naapna shuru kiya. Paanch regularities saamne aayin, aur saath milkar woh atoms ke hone ka saboot ban gayin.

1.5.1 Law of Conservation of Mass

French chemist Antoine Lavoisier (1743–1794) har cheez ko tolte the. Sealed glass vessels mein tin ko garam karke unhone paaya ki total mass tab tak nahi badla jab tak vessel khola nahi gaya aur hawa andar nahi ghusi. Aise kai experiments se unhone nishkarsh nikala ki react karne wale substances kul milakar kabhi matter na paate hain na khote hain, aur yeh idea 1789 ki apni textbook mein likha.

LawLaw of conservation of mass

Kisi bhi physical ya chemical change mein, change ke baad maujood substances ka total mass change se pehle ke total mass ke barabar hota hai.

Pehli nazar mein yeh law galat lag sakta hai: jalti mombatti halki ho jaati hai aur jang lagti keel bhaari. Dono cases mein koi gas nikalti hai ya judti hai: flame se carbon dioxide aur water vapour bahar nikal jaate hain, aur iron hawa se oxygen le leta hai. System ko un gases ke saath tolo to total same rehta hai (Fig. 1.9).

2/3Soda react karta hai aur carbon dioxide vinegar se bulbulon ke roop mein nikalti hai, lekin cap use rok leta hai: ab bhi $152.36 g$ .

Fig. 1.9Jab tak bottle band hai, mass badal nahi sakta; yeh tabhi girta hai jab carbon dioxide ko bahar nikalne diya jaata hai.NCERT p. 14

Digital balance par vinegar ki ek capped plastic bottle, jiske andar baking soda ki ek chhoti tube khadi hai. Step 1, band, milane se pehle: 152.36 g. Step 2, ab bhi band: tube jhuk gayi hai, liquid bulbulon se bhar gaya hai, aur reading ab bhi 152.36 g hai. Step 3, cap khula: dashed arrows bottle se gas nikalte dikhate hain aur reading 151.88 g tak gir gayi hai.

Try karke dekho

Band bottle mein fizz ko tolo

Tumhe chahiye

screw cap ke saath $1 L$ ki plastic soft-drink bottle
$100 m L$ vinegar
lagbhag $2 g$ baking soda (aadha teaspoon)
ek chhoti plastic tube ya kaagaz ki ek purdi
$0.1 g$ ya usse behtar padhne wala balance
safety goggles

Pehle guess karo

Cap band rehte hue, fizz rukne ke baad balance kya dikhayega?

Zyada reading, kyunki ek gas bani haiWahi reading jo milane se pehle thiKam reading, kyunki soda ghul gaya hai

Vinegar ko bottle mein daalo.
Baking soda ko chhoti tube (ya kaagaz ki purdi) mein rakho aur use dhyaan se neeche utaro taaki woh vinegar ko chhue bina seedhi khadi rahe.
Cap ko kaskar band karo. Poori bottle ko tolo aur mass record karo.
Bottle ko jhukao taaki soda vinegar mein gir jaaye. Jab fizz ruk jaaye, cap band rakhte hue dobara tolo.
Bottle ka muh sabse door rakho aur cap ko dheere-dheere dheela karke gas bahar nikalne do. Cap ko pan par bottle ke paas rakho aur dobara tolo.

Table 1.7Tumhari readings

Stage	Mass (g)
Milane se pehle
Fizz ke baad, cap band
Gas nikalne ke baad

Tumhari entries apne aap save hoti hain.

1.5.2 Law of Definite Proportions

French chemist Joseph Proust (1754–1826) ne, lagbhag 1799 mein Spain mein kaam karte hue, bilkul alag sources se ek compound ke samples ko analyse kiya aur hamesha elements ke mass ke hisaab se same proportions paaye. Pure water iska ek modern example hai.

Table 1.8Teen sources se pure water ki compositionNCERT p. 15

Sample ka source	Hydrogen (mass se %)	Oxygen (mass se %)
Distilled baarish ka paani	11.19	88.81
Distilled Ganga ka paani	11.19	88.81
Hydrogen jalakar banaya gaya	11.19	88.81

LawLaw of definite proportions

Ek diye gaye compound mein hamesha same elements mass ke hisaab se same proportions mein jude hote hain, chahe uska source ya banane ka tareeka kuch bhi ho.

Ise law of definite composition bhi kehte hain, aur isse chemist analysis se kisi substance ko pehchaan sakta hai ya uski purity check kar sakta hai. (Kuch solids, jaise iron(II) oxide, jo $F e_{0.95} O$ ke zyada kareeb hai, ki composition thodi badalti hai; aise exceptions tum aage padhoge.)

1.5.3 Law of Multiple Proportions

Elements ke kuch jode ek se zyada compound banate hain, aur 1803 mein John Dalton ne aise families mein ek pattern dekha. Carbon aur oxygen carbon monoxide aur carbon dioxide banate hain: $12.0 g$ carbon pehle mein $16.0 g$ oxygen se aur doosre mein $32.0 g$ se judta hai. Carbon ke same mass ke liye oxygen ke masses ka ratio $16 : 32 = 1 : 2$ hai, chhote whole numbers ka ratio.

LawLaw of multiple proportions

Agar do elements ek se zyada compound bana sakte hain, to pehle element ke fixed mass ke liye, alag-alag compounds mein doosre element ke masses chhote whole numbers ka ratio banate hain.

Table 1.9Nitrogen ke teen oxides

Compound	$14.0 g$ nitrogen ke saath oxygen ka mass	Ratio
dinitrogen oxide, $N_{2} O$	$8.0 g$	1
nitrogen monoxide, $N O$	$16.0 g$	2
nitrogen dioxide, $N O_{2}$	$32.0 g$	4

1.5.4 Gay Lussac's Law of Gaseous Volumes

1808 mein French chemist Joseph Louis Gay-Lussac (1778–1850) ne react karne wali gases ke volumes naape. Hydrogen ka ek volume chlorine ke bilkul ek volume se react karke hydrogen chloride ke do volumes deta hai; nitrogen ka ek volume aur hydrogen ke teen volumes ammonia ke do volumes dete hain, sab same temperature aur pressure par naape gaye.

LawGay Lussac's law of gaseous volumes

Ek hi temperature aur pressure par naapne par, react karne wali gases ke volumes, aur kisi bhi gaseous product ke volumes, simple whole-number ratios mein hote hain.

Asal mein yeh gas volumes ke liye proportions fix karta hai, aur isne ek aisi paheli khadi ki jise suljhane mein aadhi sadi lag gayi.

1.5.5 Avogadro's Law

1811 mein Italian scientist Amedeo Avogadro (1776–1856) ne suggest kiya ki kisi bhi gas ke ek diye gaye volume mein utne hi molecules hote hain jitne kisi doosri gas ke same volume mein, agar temperature aur pressure same hon. Unka sabse khaas kadam tha atom ko molecule se alag karna: kisi element ke molecule mein kai atoms ho sakte the.

LawAvogadro's law

Ek diye gaye temperature aur pressure par, kisi bhi gas ke fixed volume mein same number of molecules hote hain, gas chahe koi bhi ho.

Fig. 1.10 dikhata hai ki yeh kyun zaroori tha. Agar hydrogen aur chlorine akele, na tootne wale atoms hote, to dono ke ek-ek volume mein barabar atoms hote, aur unke jode banne se hydrogen chloride ka sirf ek volume banta; Gay-Lussac ne do naape. Agar har molecule mein do atoms hon, to har $H_{2}$ aur $C l_{2}$ milkar do HCl molecules dete hain, aur volume dugna ho jaata hai, jaisa observe hua.

3/3 $H_{2}$ aur $C l_{2}$ molecules ke saath har jode se do HCl molecules bante hain, isliye volume dugna hota hai: sahi.

Fig. 1.10Sirf diatomic molecules hi samjhate hain ki hydrogen ka ek volume aur chlorine ka ek volume hydrogen chloride ke do volumes kyun dete hain.NCERT Fig. 1.9 · p. 16

Ek-ek volume ki do gas syringes (hydrogen, chlorine), unke neeche dugni lambi syringe jismein hydrogen chloride ke do volumes hain; ek key hydrogen ko chhote aur chlorine ko bade circles se dikhati hai. Step 1 sirf volumes dikhata hai. Step 2 unhe akele atoms se bharta hai: chaar H aur chaar Cl se chaar HCl bante hain jo product syringe ka aadha hissa bharte hain, baaki 'predicted: empty' mark hai, faisla 'Akele atoms: 1 volume, galat'. Step 3 diatomic molecules use karta hai: chaar H2 aur chaar Cl2 se aath HCl bante hain jo poori syringe bhar dete hain, faisla '2 volumes, sahi'.

Dalton aur unke zamaane ke zyadatar chemists yeh maanne ko taiyaar nahi the ki ek jaise atoms jode bana sakte hain, isliye Avogadro ke idea ko kaafi had tak nazarandaaz kiya gaya. 1860 mein chemists Karlsruhe, Germany mein pehli international chemistry conference mein mile, taaki atomic masses par confusion door ho. Wahan Italian chemist Stanislao Cannizzaro ne ek pamphlet baanta jo dikhata tha ki Avogadro ki hypothesis se consistent atomic masses milte hain, aur aakhirkar yeh idea maan liya gaya.

Quick check

3 mein se 1

Sulfur ke ek oxide mein

32 g

sulfur

32 g

oxygen se juda hai; doosre mein

32 g

sulfur

48 g

oxygen ke saath hai. Yeh data kaun sa law dikhata hai?

Law of conservation of massGay Lussac's law of gaseous volumesLaw of multiple proportionsAvogadro's law

Answer dekho

Answer (C) Law of multiple proportions

Same do elements ke do compounds: fixed

32 g

sulfur ke liye oxygen masses

32 : 48 = 2 : 3

hain, ek chhota whole-number ratio. Yeh multiple proportions hai; definite proportions sirf ek compound ki baat karta.

1.6 Dalton's Atomic Theory

Greek philosopher Democritus (lagbhag 460–370 BCE) ne matter ke sabse chhote particles ko atomos, yaani 'jo kaata na ja sake', kaha, aur Kanada ke paramanu bhi aisa hi idea the, lekin dono philosophical andaaze the. English schoolteacher John Dalton (1766–1844) ne atoms ko upar ke laws ke masses se jodkar scientific banaya. Unki A New System of Chemical Philosophy (1808) ne, aaj ke shabdon mein, yeh daave kiye:

Saara matter bahut hi chhote particles se bana hai jinhe atoms kehte hain, jo chemical changes mein na divide ho sakte hain na nasht.
Kisi diye gaye element ke saare atoms ek jaise hote hain, mass mein bhi; alag elements ke atoms ke masses alag hote hain.
Compounds tab bante hain jab alag elements ke atoms fixed, chhote whole-number ratios mein judte hain.
Chemical reaction sirf atoms ko rearrange karta hai. Koi atom na banta hai na nasht hota hai.

Yeh daave mass laws ko samjhate hain. Agar atoms sirf rearrange hote hain (daava 4), to total mass nahi badal sakta (Fig. 1.11). Fixed mass wale atoms ka fixed whole-number ratio (daave 2 aur 3) fixed mass composition deta hai. Aur kyunki atoms poori units ki tarah judte hain, same elements ke doosre compound mein poore extra atoms hote hain, isiliye multiple proportions ke chhote whole-number ratios aate hain.

3/3Naye bonds bante hain: ek carbon dioxide aur do water molecules, bilkul unhi atoms se bane.

Fig. 1.11Reaction mein atoms sirf partners badalte hain: pehle aur baad mein ek carbon, chaar hydrogen aur chaar oxygen atoms.NCERT p. 16

Step 1: reactants, ek methane molecule (ek carbon chaar hydrogens ke saath) aur do oxygen molecules, ginti 'C 1, H 4, O 4'. Step 2: saare nau atoms alag hokar beech ki ek row mein, same ginti ke saath. Step 3: wahi atoms dobara group hokar ek linear carbon dioxide molecule aur do bent water molecules, same ginti ke saath. Ek arrow par label hai 'atoms regroup'.

Theory mein kamiyan thin. Yeh Gay-Lussac ke volume ratios ko nahi samjha paayi, kyunki Dalton do ek jaise atoms wale molecules ko nahi maante the, aur yeh is baare mein kuch nahi kehti thi ki atoms kyun judte hain. Baad ke kaam ne dikhaya ki atoms ko electrons, protons aur neutrons mein toda ja sakta hai (Unit 2) aur ek element ke atoms ke mass alag ho sakte hain (isotopes, Section 1.7.2). Phir bhi, fixed ratios mein atoms ka rearrange hona har chemical equation ka aadhaar hai.

Quick check

2 mein se 1

Dalton ka kaun sa daava law of multiple proportions ko sabse achhe se samjhata hai?

Reactions mein atoms rearrange hote hain, na bante hain na nasht hote hainAtoms poori units ki tarah chhote whole-number ratios mein judte hainAlag elements ke atoms ke masses alag hote hainMatter bahut chhote particles se bana hai

Answer dekho

Answer (B) Atoms poori units ki tarah chhote whole-number ratios mein judte hain

Same elements ke doosre compound mein poore extra atoms hote hain (CO versus

C O_{2}

), isliye extra oxygen mass ek poora multiple hota hai. Atoms ka conservation iske bajaye mass ke conservation ko samjhata hai.

1.7 Atomic aur Molecular Masses

Agar reactions atoms ko fixed ratios mein rearrange karte hain, to har kind ke atom ka weight jaan lene se atoms ke ratios grams ke ratios mein badal jaate hain.

1.7.1 Atomic Mass

Atomic masses relative masses hote hain. 1961 se reference carbon-12 atom ( $^{12} C$ ) hai, jise bilkul 12 units diye gaye hain. Relative kyun? Ek carbon atom, lagbhag $2 \times 10^{- 23} g$ , kisi bhi balance ke liye bahut halka hai, isliye nineteenth-century ke chemists atoms ko sirf judne wale elements ke masses ke through compare kar sakte the, shuruaat hydrogen ko 1 kehkar karte hue. Aaj ka mass spectrometer atomic masses ko seedhe aur precisely naapta hai, lekin unhe ab bhi inhi units mein report karta hai.

Definition

Atomic mass unit (u)

Carbon-12 ke ek atom ke mass ka bilkul $1 / 12$ hissa, yaani $1.6605 \times 10^{- 24} g$ ; pehle amu likha jaata tha, ise dalton (Da) bhi kehte hain.

Atomic mass unit

\begin{aligned} 1 u & = \frac{1}{12} m ⁣ (^{12} C) \\ = 1.6605 \times 10^{- 24} g \end{aligned}

(1.6)

Kisi atom ka mass u mein likhne ke liye uske grams wale mass ko $1.6605 \times 10^{- 24} g$ se divide karo: $5.8067 \times 10^{- 23} g$ wale chlorine-35 atom ka atomic mass $34.969 u$ hai. Purana 'amu' ab u likha jaata hai, yaani unified atomic mass unit.

1.7.2 Average Atomic Mass

Zyadatar natural elements isotopes ke mixtures hote hain, yaani ek element ke alag masses wale atoms. Periodic table mein atomic mass ek natural sample ka average hai, jismein har isotope ko uske kitna common hone ke hisaab se weight diya jaata hai:

Average atomic mass

\overset{ˉ}{A} = \sum_{i} x_{i} A_{i}

(1.7)

jahan

$x_{i}$: isotope $i$ ki fractional abundance (per cent ÷ 100)
$A_{i}$: isotope $i$ ka atomic mass

3/3Har mass ko uski abundance se weight dene par $63.55 u$ milta hai, jo periodic table wali value hai.

Fig. 1.12Weighted average wahan baithta hai jahan bars balance hongi, zyada abundant isotope ke kareeb.NCERT p. 17

62 se 66 u tak mass axis. Step 1: 62.93 u par copper-63 ka ek lamba bar (69.15 per cent) aur 64.93 u par copper-65 ka chhota dashed bar (30.85 per cent). Step 2: plain average, 63.93, par ek dashed line. Step 3: woh line feeki pad jaati hai aur balance-point triangle wali ek solid line weighted average, 63.55 u, ko mark karti hai, jo copper-63 bar ke kareeb hai.

ExampleNCERT p. 17

Copper ka average atomic mass

Natural copper mein $69.15 %$ $^{63} C u$ ( $62.9296 u$ ) aur $30.85 %$ $^{65} C u$ ( $64.9278 u$ ) hota hai. Copper ka average atomic mass nikalo.

Pehle khud try karo. Phir solution ek-ek step karke kholo.

1.7.3 Molecular Mass

Molecular mass ek molecule ke saare atoms ke atomic masses ka sum hai. Ammonia, $N H_{3}$ ke liye: $14.007 + 3 (1.008) = 17.031 u$ . Carbon dioxide, $C O_{2}$ ke liye: $12.011 + 2 (15.999) = 44.009 u$ .

1.7.4 Formula Mass

Ionic compounds mein alag molecules nahi hote. Solid sodium chloride $N a^{+}$ aur $C l^{-}$ ions ki ek vishaal lattice hai, har ion doosre kind ke chhah ions se ghira hota hai, aur tolne ke liye koi 'NaCl molecule' nahi hota. Hum sabse simple formula, yaani formula unit, ke atomic masses jodkar formula mass nikalte hain. Calcium chloride, $C a C l_{2}$ ke liye: $40.078 + 2 (35.45) = 110.98 u$ .

Example 1.1NCERT Problem 1.1 · p. 18

Paracetamol ka molecular mass

Paracetamol, bukhaar ki aam dawai, ka formula $C_{8} H_{9} N O_{2}$ hai. Iska molecular mass calculate karo. (Atomic masses: C $12.011$ , H $1.008$ , N $14.007$ , O $15.999 u$ .)

Pehle khud try karo. Phir solution ek-ek step karke kholo.

Quick check

3 mein se 1

Potassium sulfate,

K_{2} S O_{4}

ka formula mass nikalo (K

39.10

, S

32.06

, O

16.00 u

Answer dekho

Answer 174.26 u

2 (39.10) + 32.06 + 4 (16.00) = 78.20 + 32.06 + 64.00 = 174.26 u

1.8 Mole Concept aur Molar Masses

Bank sikkon ki thaili ginne ki jagah use tol leta hai, aur paper ki dukaan sheets ko 500 ke ream mein bechti hai. Chemists ke saamne yahi problem bahut bade scale par hai: ek chutki namak mein lagbhag $10^{22}$ ions hote hain. Unki ginti ki unit mole (मोल) hai; amount of substance $n$ , moles mein, ek SI base quantity hai.

Definition

Mole (mol)

Amount of substance ki SI base unit: kisi bhi cheez ka ek mole uski specified entities ka bilkul $6.02214076 \times 10^{23}$ hota hai, chahe woh atoms, molecules, ions, electrons ya particles ke defined groups hon.

ExampleNaCl ka $1 m o l$ yaani $6.022 \times 10^{23}$ formula units.

Per mole entities ki sankhya Avogadro constant hai, $N_{A} = 6.02214076 \times 10^{23} m o l^{- 1}$ (sirf number ko Avogadro number kehte hain), jo 2019 se definition se exact hai. Iski value mole aur u ko bilkul fit kar deti hai: $N_{A}$ atomic mass units milkar ek gram banti hain.

Avogadro constant aur u

\begin{aligned} N_{A} \times 1 u \\ = 6.0221 \times 10^{23} \\ \times 1.6605 \times 10^{- 24} g \\ = 1.000 g \end{aligned}

(1.8)

Din-raat ek particle per second ginte raho, to ek mole ginne mein lagbhag $1.9 \times 10^{16}$ saal lagenge, jo universe ki umar se das laakh guna se bhi zyada hai. Hydrogen atoms ka ek mole, water molecules ka ek mole ya NaCl formula units ka ek mole, sab mein same $6.022 \times 10^{23}$ entities hoti hain.

Kisi substance ka molar mass (मोलर द्रव्यमान) $M$ yeh hai ki uska ek mole kitne grams ka hota hai, $g m o l^{- 1}$ mein. Eq. (1.8) ki wajah se $M$ ka number u mein atomic, molecular ya formula mass ke barabar hota hai: $C O_{2}$ $44.01$ , $N H_{3}$ $17.03$ aur $C a C l_{2}$ $110.98 g m o l^{- 1}$ . (2019 se carbon-12 ka molar mass bilkul $12 g m o l^{- 1}$ nahi hai, lekin fark ek billion mein ek hisse se bhi kam hai.)

Definition

Molar mass

Kisi substance ke ek mole ka weight grams mein; number mein yeh u mein uske atomic, molecular ya formula mass ke barabar hota hai.

Example $M (H_{2} O) = 18.02 g m o l^{- 1}$ .

Teen relations moles ko naapi ja sakne wali cheezon se jodte hain; saath milkar yeh Fig. 1.13 ka 'mole map' banate hain.

Mass se moles

n = \frac{m}{M}

(1.9)

jahan

$m$: g mein mass
$M$: $g m o l^{- 1}$ mein molar mass

Particles ki sankhya

N = n N_{A}

(1.10)

STP par gas ka volume

V = n \times 22.7 L m o l^{- 1}

(1.11)

jahan

$V$: STP ( $273.15 K$ , $1 b a r$ ) par ideal gas ka volume

4/4STP par gas ka ek mole $22.7 L$ jagah gherta hai.

Fig. 1.13Har conversion moles se hokar jaata hai: molar mass, Avogadro constant ya molar volume se divide ya multiply karo.NCERT Fig. 1.11 · p. 18

Beech mein moles label wala ek box. Step 1: sirf woh, saath mein likha 1 mol = 6.022 guna das ki power 23 entities. Step 2: left mein mass box, arrows par likha M se divide (moles tak) aur M se multiply (wapas). Step 3: right mein particles box, arrows par N A se multiply aur N A se divide. Step 4: neeche STP ke liye gas volume box, arrows par 22.7 L se multiply aur 22.7 L se divide.

Example

Ek tablet mein molecules ginna

Ek tablet mein $500 m g$ paracetamol ( $M = 151.17 g m o l^{- 1}$ ) hai. Ismein kitne (a) moles paracetamol, (b) paracetamol molecules aur (c) carbon atoms hain?

Pehle khud try karo. Phir solution ek-ek step karke kholo.

Quick check

3 mein se 1

9.0 g

paani (

M = 18.0 g m o l^{- 1}

) mein kitne water molecules hain? Answer scientific notation mein do.

Answer dekho

Answer 3.011e+23

n = 9.0 / 18.0 = 0.50 m o l

;

N = 0.50 \times 6.022 \times 10^{23} = 3.0 \times 10^{23}

molecules.

1.9 Percentage Composition

Naye compound ke liye pehla sawaal yeh hai ki ismein kaunse elements hain, aur kis proportion mein; jaane-pehchaane compound ke liye yahi data uski purity check karta hai, jaise jab fertiliser ka nitrogen content uske label se match kiya jaata hai. Kisi element ka mass percentage formula se nikalta hai:

Kisi element ka mass per cent

w_{E} = \frac{a A_{E}}{M} \times 100 %

(1.12)

jahan

$a$: formula mein element E ke atoms ki sankhya
$A_{E}$: E ka atomic (molar) mass
$M$: compound ka molar mass

Example

Kaun sa fertiliser zyada nitrogen deta hai?

Urea, $C O (N H_{2})_{2}$ , aur ammonium sulfate, $(N H_{4})_{2} S O_{4}$ mein nitrogen ke mass percentage ko compare karo. (C $12.011$ , H $1.008$ , N $14.007$ , O $15.999$ , S $32.06 u$ .)

Pehle khud try karo. Phir solution ek-ek step karke kholo.

1.9.1 Empirical Formula aur Molecular Formula

Percentages ulti disha mein bhi kaam karte hain, aur formula de dete hain. Empirical formula (मूलानुपाती सूत्र) atoms ka sabse simple whole-number ratio dikhata hai; molecular formula ek molecule mein asli sankhya dikhata hai. Glucose, $C_{6} H_{12} O_{6}$ , ka empirical formula $C H_{2} O$ hai, benzene ( $C_{6} H_{6}$ ) ka $C H$ hai, aur water ke liye dono formulas $H_{2} O$ hain.

Definition

Empirical formula

Woh formula jo compound mein har element ke atoms ka sabse simple whole-number ratio dikhata hai.

ExampleGlucose, $C_{6} H_{12} O_{6}$ ke liye $C H_{2} O$ .

Mass percentages se empirical formula milta hai; phir molar mass se molecular formula milta hai (Fig. 1.14):

Maan lo sample $100 g$ ka hai, taaki har mass percentage grams mein mass ban jaaye.
Har mass ko element ke atomic mass se divide karke atoms ke moles nikalo.
Har mole value ko sabse chhoti value se divide karo.
Agar ratios whole numbers nahi hain, to sabko ek chhote factor se multiply karo: $.5$ par khatam hone wale ratio ko $\times 2$ chahiye; $.33$ ya $.67$ par khatam hone wale ko $\times 3$ chahiye. $1.5$ ko kabhi $2$ tak round mat karo.
Empirical formula likho aur uska empirical formula mass jodo.
$n = M / (empirical formula mass)$ nikalo, jo whole number hona chahiye, aur har subscript ko $n$ se multiply karo.

4/4 $n = 62.07 / 31.03 = 2$ , isliye molecular formula $C_{2} H_{6} O_{2}$ hai.

Fig. 1.14Grams moles bante hain, moles ek ratio bante hain, aur molar mass ratio ko asli formula tak scale up karta hai.NCERT p. 20

Step 1: 100 g ka bar mass ke hisaab se carbon 38.7 g, hydrogen ki patli 9.7 g ki slice aur oxygen 51.6 g mein bata hua. Step 2: moles ka bar, carbon 3.22, hydrogen 9.66 aur oxygen 3.22, to ab hydrogen ka hissa sabse chauda hai. Step 3: sabse chhoti value se divide karne par C : H : O = 1 : 3 : 1, yaani empirical formula CH3O. Step 4: molar mass 62.07 ko empirical formula mass 31.03 se divide karne par n = 2, isliye molecular formula C2H6O2 hai.

Example 1.2NCERT Problem 1.2 · p. 19

Ek coolant ka formula

Ethylene glycol, jo vehicle radiators mein antifreeze ki tarah use hota hai, mein mass ke hisaab se $38.70 %$ carbon, $9.74 %$ hydrogen aur $51.56 %$ oxygen hai. Iska molar mass $62.07 g m o l^{- 1}$ hai. Iske empirical aur molecular formulas nikalo. (C $12.011$ , H $1.008$ , O $15.999$ )

Pehle khud try karo. Phir solution ek-ek step karke kholo.

Quick check

3 mein se 1

Calcium carbonate,

C a C O_{3}

(Ca

40.08

, C

12.01

, O

16.00

) mein oxygen ka mass percentage kya hai?

Answer dekho

Answer 47.96 %

M = 40.08 + 12.01 + 48.00 = 100.09 g m o l^{- 1}

;

w_{O} = 48.00 / 100.09 \times 100 % = 47.96 %

1.10 Stoichiometry aur Stoichiometric Calculations

Stoichiometry (रससमीकरणमिति), Greek stoicheion ('element') aur metron ('measure') se bana word, ek balanced equation ka use karke zaroori reactants aur bane products ke masses, ya gas volumes, calculate karti hai. Propane ka jalna lo, jo camping stoves ki gas hai:

Propane ka jalna

\begin{aligned} C_{3} H_{8} (g) + 5 O_{2} (g) \\ \overset{}{\to} 3 C O_{2} (g) \\ + 4 H_{2} O (g) \end{aligned}

(1.13)

Propane aur oxygen reactants hain, carbon dioxide aur water products. State symbols dikhate hain (s) solid, (l) liquid, (g) gas ya (aq) paani mein ghula hua. Aage likhe stoichiometric coefficients (na likha ho to 1 maano) woh ratio batate hain jismein molecules, aur isliye moles, react karte aur bante hain:

Table 1.10Eq. (1.13) ko padhne ke chaar tareeke, water ko vapour maankarNCERT p. 20

	$C_{3} H_{8}$	$O_{2}$	$C O_{2}$	$H_{2} O$
molecules	1	5	3	4
moles	1	5	3	4
gas volumes (same $T$ , $p$ )	1	5	3	4
g mein mass	44.1	160.0	132.0	72.1

Volume wali row Avogadro ke law se aur mass wali row molar masses se aati hai; reactants aur products dono ka total $204.1 g$ hai, jaisa conservation of mass kehta hai. Kyunki coefficients mole ratios hain, har problem ek hi raaste par chalta hai: data ko moles mein badlo, mole ratio lagao, aur wapas jo units chahiye unmein badlo.

Step by step

Butane ke jalne ko balance karna

Step 1 / 5

Formulas likho

Butane oxygen mein jalkar carbon dioxide aur water deta hai: $C_{4} H_{10} + O_{2} \overset{}{\to} C O_{2} + H_{2} O$ (abhi balanced nahi).

1 / 5

Example 1.3NCERT Problem 1.3 · p. 22

Gas cylinder se carbon dioxide

Ghar ke LPG cylinder mein $14.2 k g$ gas hoti hai. Gas ko pure butane, $C_{4} H_{10}$ ( $M = 58.12 g m o l^{- 1}$ ), maankar batao ki poori gas jalne par kitne mass ki carbon dioxide ( $M = 44.01 g m o l^{- 1}$ ) banegi?

Pehle khud try karo. Phir solution ek-ek step karke kholo.

Example 1.4NCERT Problem 1.4 · p. 22

Kitna magnesium?

$10.0 g$ magnesium oxide banane ke liye kitne moles, aur kitne grams, magnesium jalana padega? (Mg $24.31$ , O $16.00$ )

Pehle khud try karo. Phir solution ek-ek step karke kholo.

1.10.1 Limiting Reagent

Reactants shayad hi kabhi bilkul equation ke ratio mein milaye jaate hain. 120 auto-rickshaw bodies aur 300 wheels wali factory sirf $300 / 3 = 100$ autos poore kar sakti hai, aur 20 bodies bach jaati hain: wheels output ko limit karte hain. Reaction mein, jo reactant sabse pehle khatam hota hai woh use rok deta hai, chahe baaki kitne bhi bache hon.

Definition

Limiting reagent

Woh reactant jo sabse pehle poora khatam hota hai; yeh product ki maximum matra tay karta hai, aur baaki reactants excess mein hote hain.

Limiting reagent (सीमांत अभिकर्मक) dhoondhne ke liye har reactant ko moles mein badlo aur uske coefficient se divide karo; jo result sabse chhota ho, woh limiting hai. Seedhe masses, ya seedhe moles bhi, dhokha de sakte hain (Fig. 1.15).

3/3Chhah $H_{2} O$ bante hain aur do $O_{2}$ bachte hain: hydrogen limiting reagent hai.

Fig. 1.15Har oxygen molecule ke liye do hydrogen molecules chahiye, isliye hydrogen pehle khatam hoti hai, haalaanki hydrogen molecules oxygen molecules se zyada hain.NCERT p. 21

Before aur after boxes ek arrow se jude. Step 1: chhah hydrogen molecules (chhote khule circles ke jode) aur paanch oxygen molecules (bade shaded circles ke jode). Step 2: do hydrogen aur ek oxygen molecule ke teen groups ke charon taraf dashed loops; do oxygen molecules spare mark kiye gaye hain. Step 3: after box mein chhah water molecules aur do bache hue oxygen molecules hain, caption ke saath 'hydrogen pehle khatam: limiting'.

Example 1.5NCERT Problem 1.5 · p. 22

Thermite se rails ki welding

Indian Railways rails ko thermite reaction, $2 A l + F e_{2} O_{3} \overset{}{\to} A l_{2} O_{3} + 2 F e$ , se weld karta hai, jo pighla hua iron deta hai. Ek charge mein $54.0 g$ Al aur $200 g$ $F e_{2} O_{3}$ hai. Nikalo (a) limiting reagent, (b) bane iron ka mass aur (c) bache excess reactant ka mass. (Al $26.98$ , Fe $55.85$ , $F e_{2} O_{3}$ $159.69 g m o l^{- 1}$ )

Pehle khud try karo. Phir solution ek-ek step karke kholo.

InteractiveStoichiometry lab

Buttons paanch balanced reactions mein se ek chunte hain (hydrogen ka jalna, ammonia synthesis, methane ka jalna, thermite, zinc ke saath hydrochloric acid). Number boxes wale do sliders reactant masses ko grams mein set karte hain. Ek table har reactant ka molar mass, moles aur coefficient se divide kiye moles deti hai, aur sabse chhote wale ko limiting batati hai. Bars har substance ke moles pehle aur baad mein dikhate hain, aur ek status line product masses, bacha hua excess aur yeh check deti hai ki total mass nahi badla.

Fig. 1.16Ek reaction chuno aur har reactant ka mass set karo. Lab moles mein convert karta hai, limiting reagent dhoondhta hai aur dikhata hai ki end mein har cheez kitni bachi.

Quick check

3 mein se 1

2 H_{2} + O_{2} \overset{}{\to} 2 H_{2} O

ke liye ek vessel mein

3.0 m o l

H_{2}

aur

2.0 m o l

O_{2}

hai. Limiting reagent kaun sa hai?

Oxygen, kyunki woh kam haiHydrogenKoi nahi: dono bilkul sahi ratio mein hainDono saath mein khatam hote hain

Answer dekho

Answer (B) Hydrogen

H_{2}

3.0 / 2 = 1.5

;

O_{2}

2.0 / 1 = 2.0

. Hydrogen limiting hai;

0.5 m o l

oxygen bach jaati hai, haalaanki woh kam thi.

1.10.2 Solutions mein Reactions

Lab ke zyadatar reactions solution mein kiye jaate hain, jahan ghule hue particles aasaani se milte hain, isliye humein solution ka concentration chahiye: ek diye gaye amount mein kitna solute hai. Chaar measures aam hain.

1. Mass per cent (w/w %) $100 g$ solution mein solute ka mass hai:

Mass per cent

w = \frac{m_{solute}}{m_{solution}} \times 100 %

(1.14)

jahan

$m_{solution}$: solute ka mass + solvent ka mass

2. Mole fraction solution ke saare moles ka woh hissa hai jo ek component ka hai. B mein A ke solution ke liye:

Mole fraction

\begin{array}{c} x_{A} = \frac{n_{A}}{n_{A} + n_{B}} \\ x_{A} + x_{B} = 1 \end{array}

(1.15)

Saare components ke mole fractions (मोल अंश) milkar 1 hote hain, aur mole fraction ki koi unit nahi hoti.

Example 1.6NCERT Problem 1.6 · p. 23

Fasalon ke liye urea spray

Kisaan kabhi-kabhi fasalon par urea solution spray karte hain. Ek solution $25.0 g$ urea ( $M = 60.06 g m o l^{- 1}$ ) ko $225 g$ paani ( $M = 18.02 g m o l^{- 1}$ ) mein gholkar banaya gaya hai. Nikalo (a) urea ka mass per cent aur (b) urea aur water ke mole fractions.

Pehle khud try karo. Phir solution ek-ek step karke kholo.

3. Molarity ( $M$ ) laboratory mein sabse zyada use hone wala measure hai.

Definition

Molarity

Ek litre solution mein solute ke moles ki sankhya; unit $m o l L^{- 1}$ , M likha jaata hai.

Example $0.20 m o l$ NaCl ko $1.0 L$ solution tak banaya jaaye to woh $0.20 M$ hai.

Molarity

molarity = \frac{n}{V}

(1.16)

jahan

$n$: solute ke moles
$V$: litres mein solution ka volume

Jaani hui molarity (मोलरता) wale solutions aamtaur par ek zyada concentrated stock solution ko dilute karke banaye jaate hain. Paani milane se volume badalta hai lekin solute ke moles nahi, isliye pehle ke moles baad ke moles ke barabar hote hain (Fig. 1.17):

Dilution

M_{1} V_{1} = M_{2} V_{2}

(1.17)

jahan

$M_{1}, V_{1}$: liye gaye stock ki molarity aur volume
$M_{2}, V_{2}$: dilution ke baad molarity aur volume

3/3Mark tak paani milao aur mix karo: ab bhi $0.150 m o l$ , ab $0.500 L$ mein, isliye $0.30 M$ .

Fig. 1.17Dilution solute ke unhi moles ko ek bade volume mein phaila deta hai.NCERT p. 23

Step 1: stock 6.0 M label wala beaker, solute dots se bhara, aur 25.0 mL wala pipette jismein chhah dots hain. Step 2: pipette 500 mL volumetric flask mein khaali ho gaya hai; chhah dots thode se liquid mein hain, label 0.150 mol. Step 3: flask mark tak bhar diya gaya hai; wahi chhah dots usmein phail gaye hain, label 0.30 M, saath mein note 'same moles, 20 guna volume'.

Example

Stock acid ko dilute karna

$0.30 M$ acid ka $500 m L$ banane ke liye $6.0 M$ hydrochloric acid ka kitna volume dilute karna padega?

Pehle khud try karo. Phir solution ek-ek step karke kholo.

Example 1.7NCERT Problem 1.7 · p. 24

Glucose drip ki molarity

Hospital ke $500 m L$ drip bag mein $25.0 g$ glucose, $C_{6} H_{12} O_{6}$ ( $M = 180.16 g m o l^{- 1}$ ) hai. Glucose ki molarity kya hai?

Pehle khud try karo. Phir solution ek-ek step karke kholo.

Molarity mein ek kami hai: garam hone par solution phailta hai, isliye same moles zyada litres gherte hain aur molarity gir jaati hai.

4. Molality ( $m$ ) solution ke volume ki jagah solvent ke mass ko lekar is problem se bachti hai.

Definition

Molality

Per kilogram solvent mein solute ke moles ki sankhya; unit $m o l k g^{- 1}$ , m likha jaata hai.

Example $1.00 k g$ paani mein ghuli $0.50 m o l$ sugar $0.50 m$ hai.

Molality

molality = \frac{n}{m_{solvent}}

(1.18)

jahan

$n$: solute ke moles
$m_{solvent}$: kilograms mein solvent ka mass

Masses temperature ke saath nahi badalte, isliye molality (मोललता) bhi nahi badalti. Molarity aur molality ke beech convert karne ke liye solution ki density chahiye.

Example 1.8NCERT Problem 1.8 · p. 24

Molarity se molality tak

Sulfuric acid, $H_{2} S O_{4}$ ( $M = 98.08 g m o l^{- 1}$ ), ke $2.00 M$ solution ki density $1.12 g m L^{- 1}$ hai. Iski molality nikalo.

Pehle khud try karo. Phir solution ek-ek step karke kholo.

Quick check

3 mein se 1

Thande storeroom mein banaya gaya stock solution garam lab mein use hota hai. Iske concentration ka kaun sa measure badal gaya hai?

Mass per centMole fractionMolalityMolarity

Answer dekho

Answer (D) Molarity

Garam hone se solution phailta hai, isliye molarity thodi gir jaati hai; baaki measures sirf masses ya moles use karte hain.

Recap

Summary aur key points

Chemistry yeh study karti hai ki substances kis cheez se bane hain, kaise bane hain aur kaise badalte hain; India ki chemical parampara Harappa ke crafts aur Kanada ke paramanu se lekar modern industry tak jaati hai (Chemistry ka Vikas).
Matter ka mass hota hai aur woh jagah gherta hai. Solids, liquids aur gases mein fark yeh hai ki unke particles kitne paas-paas aur kitne mobile hain, aur temperature aur pressure badalne se woh ek doosre mein badalte hain (Section 1.2.1).
Mixtures (homogeneous ya heterogeneous) physical methods se alag kiye ja sakte hain; pure substances elements (ek kind ka atom) ya compounds (fixed ratio mein jude elements) hote hain (Section 1.2.2).
Measured quantity ek number aur ek unit hoti hai. SI mein saat base units hain, har ek 2019 se nature ke ek exact constant se defined hai, aur atto se tera aur usse aage tak prefixes hain (Section 1.3.3).
Mass constant rehta hai lekin weight gravity ke saath badalta hai; $1 L = 1 d m^{3} = 1000 m L$ ; density $ρ = m / V$ ; $T = t_{C} + 273.15$ (Section 1.3.4, Section 1.3.7).
Scientific notation bahut bade aur bahut chhote numbers ko sambhalta hai. Significant figures certain digits plus ek andaaze wala digit hain; results mein sabse kam decimal places (sums) ya significant figures (products) rakhe jaate hain. Precision repeats ke beech ka mel hai, accuracy true value se nazdeeki (Section 1.4.2); unit factors units convert karte hain (Section 1.4.3).
Chemical combination ke paanch laws (conservation of mass, definite proportions, multiple proportions, gaseous volumes aur Avogadro's law) Dalton ki atomic theory tak le gaye (Section 1.5, Section 1.6).
Atomic masses carbon-12 ke relative hote hain ( $1 u$ uske mass ka barahvan hissa hai); periodic-table values isotopes ke abundance-weighted averages hain (Section 1.7).
Ek mole mein $N_{A} = 6.02214076 \times 10^{23}$ entities hoti hain; $g m o l^{- 1}$ mein molar mass u mein atomic, molecular ya formula mass ke barabar hota hai; $n = m / M$ (Section 1.8).
Mass percentages se empirical formula milta hai; phir molar mass se molecular formula milta hai (Section 1.9).
Balanced equation ke coefficients mole ratios hain; limiting reagent, jo sabse pehle khatam hota hai, product ki matra tay karta hai (Section 1.10, Section 1.10.1).
Concentration ko mass per cent, mole fraction, molarity (temperature ke saath badalti hai) ya molality (nahi badalti) mein diya ja sakta hai (Section 1.10.2).

Apna NCERT exercise question dhoondo

Hamare practice questions ncert.ai ke liye likhe gaye hain aur NCERT exercises ko follow karte hain. Apni textbook ke question se match karne wala question dhoondo; uska answer uske saath hai.

Tumhari NCERT textbook mein	Yahan practice question
NCERT Exercises 1.1	Practice Q1
NCERT Exercises 1.2	Practice Q2
NCERT Exercises 1.3	Practice Q3
NCERT Exercises 1.4	Practice Q4
NCERT Exercises 1.5	Practice Q5
NCERT Exercises 1.6	Practice Q6
NCERT Exercises 1.7	Practice Q7
NCERT Exercises 1.8	Practice Q8
NCERT Exercises 1.9	Practice Q9
NCERT Exercises 1.10	Practice Q10
NCERT Exercises 1.11	Practice Q11
NCERT Exercises 1.12	Practice Q12
NCERT Exercises 1.13	Practice Q13
NCERT Exercises 1.14	Practice Q14
NCERT Exercises 1.15	Practice Q15
NCERT Exercises 1.16	Practice Q16
NCERT Exercises 1.17	Practice Q17
NCERT Exercises 1.18	Practice Q18
NCERT Exercises 1.19	Practice Q19
NCERT Exercises 1.20	Practice Q20
NCERT Exercises 1.21	Practice Q21
NCERT Exercises 1.22	Practice Q22
NCERT Exercises 1.23	Practice Q23
NCERT Exercises 1.24	Practice Q24
NCERT Exercises 1.25	Practice Q25
NCERT Exercises 1.26	Practice Q26
NCERT Exercises 1.27	Practice Q27
NCERT Exercises 1.28	Practice Q28
NCERT Exercises 1.29	Practice Q29
NCERT Exercises 1.30	Practice Q30
NCERT Exercises 1.31	Practice Q31
NCERT Exercises 1.32	Practice Q32
NCERT Exercises 1.33	Practice Q33
NCERT Exercises 1.34	Practice Q34
NCERT Exercises 1.35	Practice Q35
NCERT Exercises 1.36	Practice Q36

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Chemistry ka Vikas2 questions
1.1 Chemistry ki Importance1 question
1.2.2 Matter ka Classification3 questions
1.3.7 Temperature3 questions
1.4.3 Dimensional Analysis3 questions
1.5.5 Avogadro's Law3 questions
1.6 Dalton's Atomic Theory2 questions
1.7.4 Formula Mass3 questions
1.8 Mole Concept aur Molar Masses3 questions
1.9.1 Empirical Formula aur Molecular Formula3 questions
1.10.1 Limiting Reagent3 questions
1.10.2 Solutions mein Reactions3 questions

Glossary · 15

Key terms (English + Hindi)

accuracyयथार्थताyathaarthata: Result true value ke kitna kareeb hai.Chapter mein pehli baar yahan aaya →
atomic mass unitपरमाणु द्रव्यमान मात्रकparmaanu dravyamaan maatrak: Carbon-12 atom ke mass ka barahvan hissa, $1.6605 \times 10^{- 24} g$ ; symbol u.

compoundयौगिकyaugik: Do ya zyada elements se bana pure substance jo mass ke hisaab se fixed ratio mein chemically jude hon.Chapter mein pehli baar yahan aaya →

elementतत्वtatva: Sirf ek kind ke atom se bana pure substance.Chapter mein pehli baar yahan aaya →
empirical formulaमूलानुपाती सूत्रmoolaanupaati sootra: Compound mein atoms ka sabse simple whole-number ratio.Chapter mein pehli baar yahan aaya →

limiting reagentसीमांत अभिकर्मकseemaant abhikarmak: Woh reactant jo sabse pehle khatam hota hai aur product ki matra limit karta hai.Chapter mein pehli baar yahan aaya →

mixtureमिश्रणmishran: Do ya zyada pure substances kisi bhi ratio mein mile hue; physical methods se alag kiye ja sakte hain.Chapter mein pehli baar yahan aaya →
molalityमोललताmolalta: Per kilogram solvent mein solute ke moles (m); yeh temperature ke saath nahi badalti.Chapter mein pehli baar yahan aaya →
molar massमोलर द्रव्यमानmolar dravyamaan: Kisi substance ke ek mole ka weight grams mein; unit $g m o l^{- 1}$ .Chapter mein pehli baar yahan aaya →
molarityमोलरताmolarta: Per litre solution mein solute ke moles (M); yeh temperature ke saath badalti hai.Chapter mein pehli baar yahan aaya →
moleमोलmol: Amount of substance ki SI unit: bilkul $6.02214076 \times 10^{23}$ entities.Chapter mein pehli baar yahan aaya →
mole fractionमोल अंशmol ansh: Ek component ke moles ko mixture ke total moles se divide karna.Chapter mein pehli baar yahan aaya →

precisionपरिशुद्धताparishuddhata: Baar-baar ke measurements aapas mein kitna milte hain.Chapter mein pehli baar yahan aaya →

significant figuresसार्थक अंकsaarthak ank: Measurement ke certain digits plus ek andaaze wala digit.Chapter mein pehli baar yahan aaya →
stoichiometryरससमीकरणमितिrassameekaranmiti: Balanced equation se reactants aur products ki matra calculate karna.Chapter mein pehli baar yahan aaya →

Chemistry ka Vikas

1.1 Chemistry ki Importance

1.2 Matter ka Nature

1.2.1 Matter ki States

1.2.2 Matter ka Classification

1.3 Matter ki Properties aur unka Measurement

1.3.1 Physical aur Chemical Properties

1.3.2 Physical Properties ka Measurement

1.3.3 International System of Units (SI)

1.3.4 Mass aur Weight

1.3.5 Volume

1.3.6 Density

1.3.7 Temperature

1.4 Measurement mein Uncertainty

1.4.1 Scientific Notation

1.4.2 Significant Figures

1.4.3 Dimensional Analysis

1.5 Chemical Combinations ke Laws

1.5.1 Law of Conservation of Mass

1.5.2 Law of Definite Proportions

1.5.3 Law of Multiple Proportions

1.5.4 Gay Lussac's Law of Gaseous Volumes

1.5.5 Avogadro's Law

1.6 Dalton's Atomic Theory

1.7 Atomic aur Molecular Masses

1.7.1 Atomic Mass

1.7.2 Average Atomic Mass

1.7.3 Molecular Mass

1.7.4 Formula Mass

1.8 Mole Concept aur Molar Masses

1.9 Percentage Composition

1.9.1 Empirical Formula aur Molecular Formula

1.10 Stoichiometry aur Stoichiometric Calculations

1.10.1 Limiting Reagent

1.10.2 Solutions mein Reactions

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