Chemistry, Third edition

8 · THE MOLE

8.7.(i)Whatmassof oxygen would be produced by heating

4.25 g of sodium nitrate?

2NaNO 3 (s)2NaNO 2 (s)O 2 (g)

(ii) What volume of oxygen, at room temperature and

pressure, does the answer to (i)represent?

8.8.When sodium hydrogen carbonate (NaHCO 3 ) is heated,

the following change occurs:

NaHCO 3 (s)Na 2 CO 3 (s)H 2 O(I)CO 2 (g)

(i) Balance the equation written above.

(ii)What is the mass of two moles of NaHCO 3?

(iii)What is the mass of CO 2 produced when 2.0 mol of

NaHCO 3 are decomposed? What is the volume of this mass at

room temperature and pressure?

(iv)What volume of carbon dioxide, at room temperature

and pressure, would be obtained if 4.2 g of NaHCO 3 were

completely decomposed?

8.9.What percentage by mass is water in the salt

MgSO 4 · 7H 2 O?

8.10.When the gas ethene is analysed, it is found to contain

85.72% carbon and 14.28% hydrogen by mass. The molar

mass of ethene is 28 g mol^1. What is its molecular formula?

8.11.Aluminium was burned in a stream of chlorine so that

it was all converted to aluminium chloride. The following

results were obtained:

Mass of aluminium at the start of the experiment 13.50 g.

Mass of aluminium chloride at the end of the experiment

66.75 g.

From these results, determine the formula of aluminium

chloride.

134

DID YOU KNOW?

Although the amount mole usually relers to small particles, it can be used to describe any objects. The

reason it isn’t used more widely is because it is such a huge number.

If every person on Earth (population six billion) were to have a mole of pounds (£) equally divided

between them at birth, and they all lived to 80, each person would have to spend about £40,000 per

secondof their lives in order to die penniless. And that excludes any interest on their savings!