2 e) Hydrogen and water

Question 1

2.25- describe the reactions of dilute hydrochloric and dilute sulfuric acids with magnesium, aluminium, zinc and iron

Answer 1

Magnesium

With dilute hydrochloric acid

Mg(s) + HCl(aq) ==> MgCl2(aq) + H2(g)

When magnesium react with dilute hydrochloric acid, it forms magnesium chloride and hydrogen gas.

With dilute sulphuric acid

Mg(s) + H2SO4(aq) ==> MgSO4(aq) + H2(g)

When magnesium react with dilute sulphuric acid, it forms magnesium sulphate and hydrogen gas.

Aluminium

With dilute hydrochloric acid

Al(s) + HCl(aq) ==> AlCl3(aq) + H2(g)

When aluminium react with dilute hydrochloric acid, it forms aluminium trichloride and hydrogen gas.

With dilute sulphuric acid

Al(s) + H2SO4(aq) ==> Al2(SO4)3(aq) + H2(g)

When aluminium react with dilute sulphuric acid, it forms aluminium sulphate and hydrogen gas.

Iron

With dilute hydrochloric acid

Fe(s) + HCl(aq) ==> FeCl2(aq) + H2

When Iron react with hydrochloric acid, it forms Iron(III) chloride and hydrogen gas.

With dilute sulphuric acid

Fe(s) + H2SO4(aq) ==> FeSO4(aq) + H2

When iron react with sulphuric acid, it forms iron sulphate and hydrogen gas.

Question 2

2.26- describe the combustion of hydrogen

Answer 2

2H2(g) + O2(g) ==> 2H2O(g)

Hydrogen gas burns in air or oxygen to form water(steam).

When hydrogen is pure, hydrogen burns quietly. However, when it is mixed with air or oxygen first, an explosion will occur if a spark or flame is applied.

Testing hydrogen

When a lighted splint is held at the mouth of the test tube that contains hydrogen gas, it will make a popping sound.

Question 3

2.27- describe the use of anhydrous copper(II) sulfate in the chemical test for water

Answer 3

Water turns white anhydrous copper(II) sulphate blue. Anhydrous copper(II) sulphate lacks water of crystallisation. Dropping water in it replaces the water of crystallisation and therefore colour changes.

CuSO4(s) + 5H2O(l) ==> CuSO4x5H2O(s)

Question 4

2.28- describe a physical test to show whether water is pure.

Answer 4

If water exactly freezes at 0oC and boils at exactly 100oC at 1 atmospheric pressure, then the water is pure.