NCERT Solutions For Class 9 Science

In a reaction, 5.3 g of sodium carbonate reacted with 6 g of acetic acid. The products were 2.2 g of carbon dioxide, 0.9 g water and 8.2 g of sodium acetate. Show that these observations are in agreement with the law of conservation of mass.

Sodium carbonate + acetic acid \rightarrow sodium acetate + carbon dioxide + water

Hydrogen and oxygen combine in the ratio of 1:8 by mass to form water. What mass of oxygen gas would be required to react completely with 3 g of hydrogen gas?

Which postulate of Dalton's atomic theory is the result of the law of conservation of mass?

Which postulate of Dalton's atomic theory can explain the law of definite proportions?

Define the atomic mass unit.

Why is it not possible to see an atom with naked eyes?

1. Write down the formulae of
(i) sodium oxide
(ii) aluminium chloride
(iii) sodium sulphide
(iv) magnesium hydroxide

2. Write down the names of compounds represented by the following formulae:
(i)\text{Al}_2(\text{SO}_4)_3
(ii) \text{CaCl}_2
(iii) \text{K}_2\text{SO}_4
(iv) \text{KNO}_3
(v) \text{CaCO}_3.

What is meant by the term chemical formula?

How many atoms are present in a
(i) \text{H}_2\text{S} molecule and
(ii) \text{PO}_4^{3-} ion?

Calculate the molecular masses ofH_2, O_2, Cl_2, CO_2, CH_4, C_2H_6, C_2H_4, NH_3, CH_3OH.

Calculate the formula unit masses of ZnO, Na_2O, K_2CO_3, given atomic masses of Zn = 65\ u, Na = 23\ u, K = 39\ u, C = 12\ u, and O = 16\ u.

A 0.24 g sample of compound of oxygen and boron was found by analysis to contain 0.096 g of boron and 0.144 g of oxygen. Calculate the percentage composition of the compound by weight.

When 3.0 g of carbon is burnt in 8.00 g oxygen, 11.00 g of carbon dioxide is produced. What mass of carbon dioxide will be formed when 3.00 g of carbon is burnt in 50.00 g of oxygen? Which law of chemical combination will govern your answer?

What are polyatomic ions? Give examples.

Write the chemical formulae of the following.
(a) Magnesium chloride
(b) Calcium oxide
(c) Copper nitrate
(d) Aluminium chloride
(e) Calcium carbonate.

Give the names of the elements present in the following compounds.
(a) Quick lime
(b) Hydrogen bromide
(c) Baking powder
(d) Potassium sulphate.

Calculate the molar mass of the following substances.

(a) Ethyne, \text{C}_2\text{H}_2

(b) Sulphur molecule, \text{S}_8

(c) Phosphorus molecule, \text{P}_4 (Atomic mass of phosphorus = 31)

(d) Hydrochloric acid, HCl

(e) Nitric acid, \text{HNO}_3