Hydrogen and Water

Question 1

Describe the reactions of dilute hydrochloric and dilute sulfuric acids with magnesium, aluminium, zinc and iron

Answer 1

Magnesium - & hydrochloric sulfuric: Rapid fizzing and hydrogen is evolved. Reaction mixture gets warm as hydrogen is produced. Magnesium gradually disappears to leave colourless solution of magnesium chloride/sulfate.

Aluminium: slow to start reacting but very vigorous after warming. Layer of aluminium oxide prevents acid reacting with aluminium but on heating the acid removes this layer. Hydrogen produced.

Zinc & Iron: react slowly in cold, rapid on heating. Hydrogen is produced as well for both.

Question 2

Describe the combustion of hydrogen

Answer 2

2H2 + O2 ——> 2H2O
Energy is supplied to break the bonds in the hydrogen molecules and in the oxygen molecule to form new bonds which are made in water.

Question 3

Describe the use of anhydrous copper(II) sulfate in the chemical test for water

Answer 3

Anhydrous copper sulfate lacks water of crystallisation and is white. Dropping water onto it replaces the water of crystallisation and turns it blue

Question 4

Describe a physical test to show whether water is pure

Answer 4

Freezes at 0 and boils at 100 at 1 atm