Atoms and Molecules — Practice

Question 1

Define one mole and state Avogadro's number.

Accepted Answer

One mole is the amount of substance containing 6.022×10²³ particles (Avogadro's number).

Question 2

Calculate the molar mass of H₂SO₄ (H=1, S=32, O=16).

Accepted Answer

2(1) + 32 + 4(16) = 98 g mol⁻¹.

Question 3

Find the molar mass of Ca₃(PO₄)₂ (Ca=40, P=31, O=16).

Accepted Answer

3(40) + 2[31 + 4(16)] = 120 + 190 = 310 g mol⁻¹.

Question 4

How many molecules are in 0.5 mole of water?

Accepted Answer

0.5 × 6.022×10²³ = 3.011×10²³ molecules.

Question 5

The vapour density of a gas is 16. Find its molecular mass.

Accepted Answer

Molar mass = 2 × V.D. = 2 × 16 = 32 g mol⁻¹.

Question 6

How many moles are in 88 g of CO₂ (M = 44)?

Accepted Answer

n = 88/44 = 2 moles.

Practice — Atoms and Molecules