Some Basic Concepts Of Chemistry

Question 1

Matter

Answer 1

Anything which has mass and occupies space is called matter
Matter can exist in three physical states solid, liquid and gas

Question 2

Solid

Answer 2

Solids have definite volume and definite shape

Question 3

Liquid

Answer 3

Liquids have definite volume but do not have definite shape

Question 4

Gas

Answer 4

Gases don’t have definite volume and definite shape

Question 5

Homogeneous mixture

Answer 5

Mixtures which have uniform composition are known as homogeneous mixtures. The different components of this mixture cannot be separated by simple physical methods.eg: sugar solution,salt solution, air, alloys

Question 6

Heterogeneous mixtures

Answer 6

Mixtures which do not have uniform composition are known as heterogeneous mixtures. The different components of this mixture can be separated by simple methods.
eg: mixture of rice and stone ,muddy water, mixture of pulses

Question 7

Elements

Answer 7

Elements consist only one type of particles maybe atoms or molecules

Question 8

Compound

Answer 8

Compound is a combination of two or more atoms of different elements

Question 9

Law of conservation of mass ( Antoine lavoisier)

Answer 9

Matter can neither be created nor destroyed

Question 10

Law of definite proportions (Joseph proust)

Answer 10

A given compound always contains exactly the same proportion of elements by weight

Question 11

Law of multiple proportions (John Dalton)

Answer 11

If two elements combine to form more than one compound the masses of one element that combine with the fixed mass of another element are in the ratio of small whole numbers

Question 12

Law of gaseous volume (Gay lussacs)

Answer 12

In gaseous reactions there is a simple ratio exists between the volume of reactants and products (at constant temperature and pressure)

Question 13

Avogadro’s law

Answer 13

Equal volumes of all gases should contain equal number of molecules (at constant temperature and pressure)

Question 14

Dalton’s Atomic theory

Answer 14

Matter consists of indivisible atoms
Atoms of one element has same properties
Atoms of different elements have different properties
Compounds are formed by the combination of atoms in a fixed ratio
Atoms are neither created nor destroyed in a chemical reaction

Question 15

Average atomic mass

Answer 15

Atomic masses of many elements have fractional values.This is because many elements occur in nature as a mixture of different isotopes so the average atomic mass is the average of all these isotopes.

Question 16

Molecular mass

Answer 16

Molecular mass is the sum of atomic masses of the elements present in a molecule

Question 17

Formula mass

Answer 17

Some compounds exist as positive and negative ions instead of molecules. So the term formula mass is used instead of molecular mass.

Question 18

Mole concept

Answer 18

A mole is defined as the amount of substance having the same number of particles as present in 12 gram of c12 isotope

Question 19

Molar mass

Answer 19

The mass of one mole of any substance is called molar mass

Question 20

Molar volume

Answer 20

The volume occupied by one mole of a gas at STP is known as molar volume. Molar volume of all gases at STP = 22.4L

Question 21

Percentage composition

Answer 21

Mass percentage of an element=mass of element in compound/molar mass of compound×100

Question 22

Empirical formula

Answer 22

Empirical formula represents the simplest whole number ratio of various atoms present in a compound

Question 23

Molecular formula

Answer 23

Molecular formula shows the exact number of different types of atoms present in a molecule

Question 24

Relation between empirical formula and molecular formula

Answer 24

Molecular formula = empirical formula × n
n = molar mass/empirical formula mass

Question 25

Limiting reagent

Answer 25

The reagent which is completely used in a reaction is known as limiting reagent or limiting reactant

Question 26

Mass percent

Answer 26

Mass percent= mass of solute/mass of solution

Question 27

Mole fraction

Answer 27

Mole fraction is the ratio of number of moles of a particular component to the total number of moles in the components to the solution

Question 28

Molarity

Answer 28

It is defined as the number of moles of solute in 1L of solution

Question 29

Molality

Answer 29

It is defined as the number of moles of solute in 1 kg of solvent

Question 30

Which is better unit molality or molarity? Explain.

Answer 30

Molarity of the solution changes with change in temperature but molality of the solution is independent of temperature. This is because volume of the solution changes with temperature but mass of the solution does not changes with temperature. So molality is a better unit than molarity.