Ncert science solutions class 9 Solutions for Chapter 3 atoms and molecules

Exercises in Chapter 3 atoms and molecules Grade 9

Atoms and Molecules – Exercise

Atoms and Molecules – Exercise 3.1

Atoms and Molecules – Exercise 3.2

Atoms and Molecules – Exercise 3.3

Atoms and Molecules – Exercise 3.5

Questions in Atoms and Molecules – Exercise

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

Write the chemical formula of the following.

(a) Magnesium chloride

(b) Calcium oxide

(d) Aluminium chloride

(e) Calcium carbonate

What is the mass of –

(a) 1 mole of nitrogen atoms?

(b) 4 moles of aluminium atoms (Atomic mass of aluminium =27)?

What is the mass of:

(a) 0.2 mole of oxygen atoms?

(b) 0.5 mole of water molecules?

Calculate the number of aluminium ions present in 0.051g of aluminium oxide.

Questions in Atoms and Molecules – Exercise 3.1

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

Questions in Atoms and Molecules – Exercise 3.2

Define the atomic mass unit?

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

Questions in Atoms and Molecules – Exercise 3.3

Write down the formulae of

(i) sodium oxide

(ii) aluminium chloride

(iii) sodium sulphide

(iv) magnesium hydroxide

What is meant by the term chemical formula?

Write down the names of compounds represented by the following formulae:

$\text { (i) } \mathrm{Al}_{2}\left(\mathrm{SO}_{4}\right)_{3}$

$\text { (ii) } \mathrm{CaCl}_{2}$

$\text { (iii) } \mathbf{K}_{2} \mathbf{S O}_{4}$

$\text { (iv) } \mathbf{K N O}_{3}$

$(\mathbf{v}) \mathbf{C a} \mathbf{C O}_{3}$

Questions in Atoms and Molecules – Exercise 3.5

Calculate the molecular masses of $\mathbf{H}_{2}, \mathbf{O}_{2}, \mathbf{C l}_{2}, \mathbf{C O}_{2}, \mathbf{C H}_{4}, \mathbf{C}_{2} \mathbf{H}_{6}, \mathbf{C}_{2} \mathbf{H}_{4}, \mathbf{N H}_{3}, \mathbf{C H}_{3} \mathbf{O H}$

If one mole of carbon atoms weighs 12grams, what is the mass (in grams) of 1 atom of carbon?

Which has more number of atoms, 100 grams of sodium or 100 grams of iron (given, atomic mass of Na = 23u, Fe = 56 u)?