Class 11 Chemistry Chapter 1 Stoichiometry Notes( Full Chapter pdf )| Important Questions

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:

Matter:

Anything that has volume as well as mass is called matter.

Atom

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 :

  • Electrons
  • Protons
  • Neutrons

Click to Watch -> What is an atom? ( in Urdu)

Characteristic Properties of Fundamental sub-atomic particles:

Molecule:

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:

Cation:

Ions bearing positive charge are called cations

Anion:

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)

simple ion: If a single atom bears +ve or –ve charge then it is called a simple ion e.g. H+, O-2.

compound ion: 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.

Recommended video:

Difference between an atom and an ion


Element:

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.

Compound:

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.


Isotope:

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:

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.   

e.g. (i)                          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 x 1.11 / 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


Chemical Formulae:

            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

similarly:

6.022 x 1023 particles =1 mole

Click to Watch -> Concept of Mole and Avogadro’s number


Notes of all the Topics of Stoichiometry with 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

Mole and Chemical Equation

Law of conservation of mass

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


Q1.What is the mass of 0.5 moles of CaCO3?

Moles of CaCO3 = 0.5 mol

Mass of CaCO3 =?

SOLUTION:

Molar mass of CaCO3 = 100 g/ mol

 FORMULA:

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

Solution:

(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  ?

Solution:

Given:

Mass of NaCl= 60g

SOLUTION:

Moles of NaCl = ?

SOLUTION:

Molar mass of NaCl= 23+35.5= 58.5g/mol

 FORMULA:

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?

Given:

Mass of ice (water) = 12g

Molar mass of water = 18g/mol

Solution:

Number of molecules of ice (water) = Mass of ice (water) x NA

Molar mass of water

Number of molecules of ice (water) = 12g x 6.022 x 1023

18g/mol

= 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       =  24  x 100    = 20 %

                                           Molar mass of MgSO4     120 

               % age of S =         Mass of S            x 100       =  32  x 100    = 26.67 %

                                           Molar mass of MgSO4     120 

               % age of O =         Mass of O           x 100       =  64  x 100    = 53.33 %

                                           Molar mass of MgSO4     120 


Q9.Aluminium sulphate hydrate [Al2(SO4)3.x H2O] contains 8.20% of Al by mass, calculate x.

Solution:

            Formula mass of Al2(SO4)3.x H2O      = 27×2 + 32×2 + 16×12 + x(1×2 + 16)

or         Formula mass of Al2(SO4)3.x H2O      = 54 + 96 + 192 + x(18)

or         Formula mass of Al2(SO4)3.x H2O      = 342 + 18x

Percentage of Al in Al2(SO4)3.x H2O = 8.20%

     But      Percentage of Al in Al2(SO4)3.x H2O =     Amount of Al in Al2(SO4)3.x H2O x 100

                                                                                     Formula mass of Al2(SO4)3.x H2O

8.20     =          54                  x 100

                                                                                     342 + 18x

Or                                            8.20 (342 + 18x)    =   5400

Or                                            2804.40 + 147.60x = 5400

Or                                            147.60x = 5400- 2804.40

Or                                             147.60x = 2595.60

Or                                            x = 2595.60 / 147.60 =   17.59   ≈ 18

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