Question

SL No. Name
Symbol/formula Molar mass
Atomic oxygen
Number of particles
present in molar mass.
6.022 x 1023 atoms of
oxygen
16g
Molecular oxygen
2
Sodium
3.
Sodium ion
4
Sodium chloride
23g
5
6.022 x 1023 units of
sodium chloride
water
6
12. Fill the following table
2. Complete the following table:​

Answer 1

Answer:

Write down the formulae of

(i) Sodium oxide

(ii) Aluminium chloride

(iii) Sodium sulphide

(iv) Magnesium hydroxide

Ans. The formulae. are

(i) Formula bf Sodium Oxide

Symbol → Na O

Charge → +1 –2

Formula → Na2O

(iii) Formula of Sodium Oxide

Symbol → Na S

Charge → + 1 –2

Formula → Na2S

(ii) Formula of aluminium chloride

Symbol → Al Cl

Charge → +3 –1

Formula → A1C13

(iv) Formula of magnesium hydroxide

Symbol → Mg OH

Charge 1

Formula → Mg(OH)2

2. Write down the names of compounds represented btthe following formulae:

(i) Al2(SO4)3 (ii) CaCl2 (iii) K2SO4 (iv) KNO3

(v) CaCO3

Ans. (i) A12(SO4)3 → Aluminium sulphate

(ii) CaC12 → Calcium chloride

(iii) K∴SO4 → Potassium sulphate

(iv) KNO3 → Potassium nitrate

(v) CaCO3 → Calcium carbonate

3. What is meant by the term chemical formula?

Ans. The chemical formula of the compound is a symbolic representation of its composition, e.g., chemical formula of sodium chloride is NaCl.

4. How many atoms are present in a

(i) H2S molecule and

(ii) PO43– ion?

Ans. (i) H2S → 3 atoms are present

(ii) PO43– → 5 atoms are present

NCERT TEXTBOOK PAGE 40

1. Calculate the molecular masses of H2, O2, C12, CO2, CH4, C2H6, C2H4, NH3, CH3OH.

Ans. The molecular masses are:

H2 ⇒ 1 × 2 → 2u

O2⇒ 16 × 2 → 32u

Cl2 ⇒ 35.5 × 2 → 71 u

CO2 ⇒ 1 × 12 + 2 × 16 = 12 +32 = 44 u

CH4 ⇒ 1 × 12 + 4 × 1 = 16 u

C2H6 ⇒�n2 × 12 + 6 × 1 = 30 u

C2H4 ⇒ (2 × 12) + (4 × 1) = 28 u

NH3 ⇒ (1 × 14) + (3 × 1) = 17 u

CH3OH ⇒ 12 + (3 × 1) + 16 + 1 = 32 u