Class 11 Chemistry Chapter 1 Stoichiometry Notes
Stoichiometry is quantitative chemistry.
“Calculations based on the law of conservation of mass, law of constant composition and balanced chemical equations are known as stoichiometric calculations.”
Basic Concepts of Chemistry Important Definitions:
Anything that has volume as well as mass is called matter.
Atom is derived from the Greek word “Atomos” meaning indivisible.
“smallest particle of matter which possesses all the properties
of that matter but which cannot exist independently”
is known as an atom e.g. O, H, N, Cl, Br etc.
Fundamental Sub-atomic particles of an atom:
3 Fundamental sub-atomic particles of atoms are as follow :
Click to Watch -> What is an atom? ( in Urdu)
Characteristic Properties of Fundamental sub-atomic particles:
It is defined as the “smallest particle of matter which possesses all the properties of that matter and which can exist independently.” e.g. O2, Cl2, C6H12O6, S8, H2O, He etc.
Click to watch -> Molecule and its types ( in Urdu)
What is an ion?
Charge carrying species is called an ion.
2 Types of Ions:
Ions bearing positive charge are called cations
Ions bearing negative charges are called anions.
The formation of cations is an endothermic process while the formation of anions is an exothermic process.
Ions are of three types.
Click to watch -> What is an ion? ( in Urdu)
If a single atom bears +ve or –ve charge then it is called a simple ion e.g. H+, O-2.
When a group of atoms bear +ve or –ve charge then it is called a compound ion e.g. NH4+, SO4-2 etc.
molecular ion: When a molecule gains or loses electrons, the resulting species is called a molecular ion e.g. CH4+, O2+, CO+, N2+ etc. Cationic molecular ions are more common than anionic molecular ions.
Difference between an atom and an ion
A substance that is made up of only one kind of atom is called an element e.g. O2, O3, Cl2, S8, He etc. There are 92 natural elements while the total elements are more than 110.
A substance that is made up of more than one kind of atoms chemically combined together, is called a compound e.g. CO2, H2SO4, C6H12O6 etc.
Atoms having the same atomic number but different atomic masses are called isotopes. e.g. Hydrogen has three isotopes protium 1H1, deuterium 1H2, tritium 1H3, Carbon has three isotopes
6C12, 6C13, 6C14, oxygen also has three isotopes 8O16, 8O17, 8O18 etc. More than 300 isotopes occur in nature including 40 radioactive isotopes. Often, elements with even atomic numbers have more isotopes and are abundant.
Click to Watch -> Isotopes definition and examples
Atomic Number (Z):
“Number of protons in the nucleus of an atom” or “Number of electrons in an atom” is called the atomic number.
Number of electrons in an atom = Z
Number of protons in an atom = Z
Number of neutrons in an atom = A – Z
Atomic masses are expressed in three ways:
(i) Mass Number (A):
The Sum of protons and neutrons in an atom is called its mass number or nucleon number.
A = Protons + Neutrons
Click to Watch -> Mass Number and Atomic Number
(ii) Relative atomic mass (Ar):
The atomic mass of an atom is compared to the mass of Carbon-12, which is called relative atomic mass e.g. relative atomic mass of Hydrogen (protium i.e. 1H1) is 1.0078 amu.
(iii) Average atomic mass (Ar):
The weight average of isotopic masses of an element is called the average atomic mass of the element.
Relative isotopic mass Relative abundance
Carbon-12 12.00000 amu 98.89%
Carbon-13 13.00335 amu 1.11%
Average atomic mass = 12.00000 x 98.89 + 13.00335 x1.11 / 100
= 12.01 amu
amu: This is a unit to measure atomic masses. It is one-twelfth of the mass of carbon-12.
1 a.m.u = 1.66 x 10-24g or 1.66 x 10-27kg
Relative molecular masses (Mr): The sum of relative atomic masses of atoms present in a molecule gives relative molecular masses
The symbolic representation of a compound that shows elements in the compound and also the ratio of their atoms is called the chemical formula.
Types of Chemical formulae
Chemical formulae are of three types:
(i) Empirical formula or Simple formula:
The formula of a compound that shows elements in the compound and their simple atomic ratio is called empirical or simple formula.
(ii) Molecular formula:
The formula of a compound that shows elements in the compound and an actual number of their atoms is called the molecular formula.
(iii) Structural formula:
The formula of a compound that shows elements in the compound, the actual number of their atoms and the arrangement of the atoms in the molecule is called the structural formula.
Click to Watch ->Types of Chemical Formula
Avogadro’s Number and Mole:
In Chemistry, a mole is defined as the amount of substance that exactly contains 6.022 x 1023 particles.
A mole is a counting device or a number like:
12 things = Dozen
144 things = Gross
2 things = Pair
1000 g = 1k g
6.022 x 1023 particles =1 mole
Click to Watch -> Concept of Mole and Avogadro’s number
Notes of all the Topics of Stoichiometry !!
Important Explanation in detail:
Mole and Avogadro’s Number | Important Questions
How do you calculate the per cent composition of an element in a compound
Law of Constant Composition(law of definite proportions)
How to find Excess Reactant and Limiting Reactant
How do you calculate the yield of a reaction
Related Important Questions for Exams !!
Q1.What is the mass of 0.5 moles of CaCO3?
Moles of CaCO3 = 0.5 mol
Mass of CaCO3 =?
Molar mass of CaCO3 = 100 g/ mol
No of moles= mass / molar mass
Mass of CaCO3 = moles. X molar mass
Mass of CaCO3 = 0.5 X100
= 50g CaCO3
Q2.Calculate the Formula mass of the following:
(i) MgSO4 (ii) C3H6O (iii) C3H8 (iv) C2H5OH (v) Al2O3
(i) formula mass of MgSO4 = 24 + 32 + 16 x 4 = 24 + 32 + 64 = 120
(ii) formula mass of C3H6O = 12 x 3 + 1 x 6 + 16 = 36 + 6 + 16 = 58
(iii) formula mass of C3H8 = 12 x 3 + 1 x 8 = 36 + 8 = 44
(iv) formula mass of C2H5OH = 12 x 2 + 1 x 6 + 16 = 24 + 6 + 16 = 46
(v) formula mass of Al2O3 = 27 x 2 + 16 x 3 = 54 + 48 = 102
(vi) formula mass of K2Cr2O7 = 39 x 2 + 52 x 2 + 16 x 7 = 78 + 104 + 112 = 294
Q3.What is the mass of one mole Carbon atom?
Ans. The mass of one mole of carbon atom is 12g.
Q4.How many moles are there in 60g of NaCl ?
Mass of NaCl= 60g
Moles of NaCl = ?
Molar mass of NaCl= 23+35.5= 58.5g/mol
No of moles= mass / molar mass
No of moles= 60 / 58.5
No of moles(n) =1.02 mol
Q5.What is formula mass?
Ans) Sum of relative atomic masses of atoms in a formula unit of a compound is called formula mass.
Q6.Calculate the number of molecules in 12g of ice?
Mass of ice (water) = 12g
Molar mass of water = 18g/mol
Number of molecules of ice (water) = Mass of ice (water) x NA
Molar mass of water
Number of molecules of ice = 12g x 6.022 x 1023
= 4.01 x 1023 molecules
Q7.Define molar volume of a gas. What will be the volume of 2.5 moles of H2 gas and 60 g of NH3 at STP.
- Volume of one mole of a gas at a given temperature and pressure is called molar volume of the gas at the given condition e.g. molar volume of a gas at STP 22.4 dm3 while molar volume of the gas at RTP is 24dm3.
Volume of H2 gas at STP = moles x 22.4dm3 = 2.5 x 22.4dm3 = 56dm3
Volume of NH3 gas at STP = ?
Moles of NH3 = mass / molar mass = 60g / 17g mol-1 = 3.53 mol
Volume of NH3 gas at STP = moles x 22.4 = 3.53 x 22.4 = 79.07 dm3
Given the equation
CH4(g) + 2O2(g) → CO2(g) + 2H2O(g) + Heat
How can this chemical equation be read in terms of particles, moles and masses?
Ans) CH4(g) + 2O2(g) → CO2(g) + 2H2O(g) + Heat
The equation shows 1 molecule of methane reacts with 2 molecules of oxygen to produce 1 molecule of carbon dioxide and 2 molecules of steam along with the liberation of heat.
Or the equation shows 1 mole of methane reacts with 2 moles of oxygen to produce 1 mole of carbon dioxide and 2 moles of steam along with the liberation of heat.
Or the equation shows 1 dm3 of methane reacts with 2 dm3 of oxygen to produce 1 dm3 of carbon dioxide and 2 dm3 of steam along with the liberation of heat.
Or the equation shows 16 g of methane reacts with 64 g of oxygen to produce 44 g of carbon dioxide and 36 g of steam along with liberation of heat.
Q8.Calculate the percentage composition of a compound. ( MgSO4 )
Molar mass of MgSO4 = 1 x 24 + 1 x 32 + 4 x 16 = 24 + 32 + 64 = 120
% age of Mg = Mass of Mg x 100
Molar mass of MgSO4
= 24 x 100 = 20
% age of S = Mass of S x 100
Molar mass of MgSO4
= 32 x 100 = 26.67 %
% age of O = Mass of O x 100
Molar mass of MgSO4
= 64 x 100 = 53.33 %
Also Read !!
Stoichiometry Important MCQ with answers and Explanation
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Class 11 Chemistry Basic Concepts of Chemistry Solved Problems :
How many molecules of water are there in 12g of ice?
Let 10 moles of H2 and 7 moles of O2 were reacted to produce H2O.Find out the limiting reactant or reagent and excess reactant.
Find the molecular mass of glucose C6H12O6 which is also known as blood sugar
Find the Molecular mass of Naphthalene C10H8 , which is used in Mothballs
Molecular Mass Important Numericals
How to Calculate Molar mass of a Compound : HCl , NH3 ,Ca(OH)2 , CO2 ,H2O , CO , NaCl
The mass of 5 moles of Element X is 60g . Calculate its Molar mass and Name the Element x .
find the formula mass of the following compounds: K2Cr2O7, C2H5OH , C3H6O, MgSO4