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« JR
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STOICHIOMETRY
STUDY NOTES

[ 1VSAQ & 1SAQ]
STOICHIOMETRY means MEASURE of ELEMENTS
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(II) Solving simple problems on mole concepts, GMW, Molar Mass
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(IV)Finding Empirical formula of a given unknown compound
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(VI)Finding Oxidation number of Elements in a Compound
(VII) Balancing an unbalanced Redox equation

Q
T

I) FIVE LAWS OF CHEMICAL COMBINATION:
1) Law of conservation of mass (Lavoisier):
In a chemical reaction, the total mass of reactants is equal to the total mass of products
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A given chemical compound 'always contains the same elements' in a 'fixed ratio by mass'
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Nitrogen and Oxygen form N2O, NO, N2O3, NO2, N2O5
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2H2(g) + O2(g) ® 2H2O(g)
Ratio of volumes of H, O, H2O is 2:1:2
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2H + O ® H2O
2 vol of H gas + 1 vol of O ® 2 vol of water vapour
2n molecules + n molecules ® 2n molecules
BULLET MASTER'S

CHEM BEATS!
Lower Class Maths …Õ g°~¡° Ratio & Proportion Rules L„¬†³¶yOz K͋²# z#ß z#ß …ÿH›ø =O\÷"Í
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[Page No
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CHEMISTRY

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II) Measuring MOLECULAR MASSES ['Universally low masses'] of atoms / molecules
1) ATOMIC MASS
[Atomic mass unit (amu), Unified mass (u), dalton (Da)]
1
1amu 1
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008 amu=1
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Ex: Molecular mass(in amu) of one H2 O molecule = 2(1
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00amu = 18
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Measuring MOLES ['Universally huge numbers'] in a substance:
1) MOLE (Unit: mol)
Amount of substance is measured interms of the SI unit mole
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023 ´ 1023 = Avogadro Number (NA) = no
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Ex: Molar mass of H2O = 18
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Ex: GMW of H2 O = 18
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L

E
L

g(weight of substance in grams)
Þweight of substance =n´GMW
M(GMW in g)

Formula 1: Number of moles n
Formula 2: Number of molecules

B

U

(weight of substance in grams) u N A
M(GMW in g)

Y

n u NA

Number of molecules = No
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B

Note 1: Molecularity is applicable on very small entities like atoms, molecules with units amu, u
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Note 3: Though Mass and Weight are different entities, in practice both are used interchangeably
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XH› Apple weight 100g J~ò`Í weight of one dozen Apples= 1200g = 1
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Mass of 1 H atom = 0
...
007 g

Weight of 2 dozen Apples = 2400g;

Weight of 1 mole of H2 molecules = 2
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0153 g
Avogadro ‹¬OY¼ ZO`Ç Ì„^Îí^ÎO>è?
ƒ’¶q° g°^Î L#ß 3"́ q°e†Ç°#Á =°Ok Avogadro ‹¬OY¼…Õ L#ß „¬~¡=¶}°=ô#° …ÿH÷øOKÇ_¨xH÷ ̋H›#°ä›½

XH› „¬~¡=¶}°=ô Kù„¬C# ~ËA䛽 8 Q®O@° „¬xKÍÀ‹ë "³ò`ÇëO 20 q°e†Ç°#Á ‹¬O=`Ǟ~Œ ‹¬=°†Ç°O „¬_È°`Ç°Ok
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CHEMISTRY

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III) EQUIVALENT WEIGHTS
Equivalent weight is the 'combining capacity' of Elements, Acids, Bases, Salts, Oxidants,
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Ex: Empirical formula of C2H4 is CH2; Empirical formula of C2H6 is CH3
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Q
T

Ex: Molecular Formula of ethane is C2H4
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E
L

Molecular formula weight
Empirical formula weight

n=

L

Molecular weight = n ´ (Empirical formula weight)

U

Note: Molecular weight = 2 ´ Vapour density

B

V) VARIOUS CONCENTRATION METHODS OF SOLUTE IN A SOLUTION
[Mass percent, Weight percent, Molarity, Mole fraction, Molality, Normality]

Y

1) Mass Percent (%):

B

Mass % of element is the Mass of element present in 100 grams of the sample of a compound
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Formula: Molarity M

No
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76/20, 21 & Page No
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CHEMISTRY

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3) MOLALITY(m)
Molality of a solvent is the number of 'moles of solute' present in one kilogram of solvent
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of moles of solute
w
1000
; m=
u
Mass of solvent in kg
GMW W(g)

4) MOLE FRACTION(c)
Mole fraction of a component is the ratio of the number of 'moles of the component' to the 'total
number of moles of all the components' present in the solution
...
of moles of component A
Mole Fraction F A =
Total no
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1)

E
L

VI) OXIDATION NUMBER:
Oxidation number it is the total number of electrons that an atom /ion gains(–) or loses (+)

L

inorder to form a chemical bond with another atom / ion
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3)

Oxidation number of a free atom = zero

4)

Oxidation number = Number of electrons, Oxygens, Hydrogens gained/lost
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6)

O
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of H is usually +1 in regular compounds but it is –1 in alkaline compounds LiH, NaH
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N
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B

A

B

Y

B

BULLET MASTER'S

CHEM BEATS!

CONCENTRATION vs INTELLIGENCE
1000 =°Ok Students L<Œß~¡#°HùO^¥O
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1) Mass % =

Mental age
mass
u 100 Verses Intelligence Quotient (IQ) =
u 100
Molar mass
Chronological age

2) Weight % =…ÿ 10th class…Õ g° Marks % x |\÷“ g° Academic Intelligence #° JOKÇ<Œ "͆ǰKÇ°ó
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4) Molality =…ÿ, JEE-Mains Percentile =¶kiQê 1000 =°Ok…Õ g° `³eq`Í@#° JOKÇ<Œ "͆ǰKÇ°ó
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6) Normality =…ÿ, g° Academic Intelligence+Scholastic Achievements ^¥Þ~Œ g° Overall ㄬuƒ#
’ °
JOKÇ<Œ "͆°Ç =KÇ°ó
...
CHEMISTRY

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5

Imp
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73/2 ]
M(GMW in g)

Formula 1: Number of moles n

Formula 2: Weight of substance = n´GMW [FPage No
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No
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of moles ´ Avagadro Number
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No
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[ FPage No
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77/ 22,23]
Empirical formula weight

L

E
L

mass of A
u 100 [FP
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74/8 ]
Formula 8: Mass % of A =
mass of solution

U

Formula 9: Molarity M

w
1000
[FP
...
74/9 ]
u
GMW V(mL)

Formula 10: Molality m

w
1000
[FP
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74/10 ]
u
GMW W(g)

A

B

Y

B

w
1000
Formula 11: Normality (N) = GEW u V(mL) [FP
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74/11 ]

B

Formula 12: For Neutralization: V1N1=V2N2
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No
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STEP 2: Write Oxidation half reaction and reduction half reaction
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STEP 4: Balance Oxygen atoms
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STEP 6: Balance charges
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STEP 8: Apply Crisscross rule if required
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STEP 10: Write the Balanced Equation

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