Form 1:
Water and Hydrogen

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Hydrogen

Occurrence

Hydrogen does not occur free in nature.

It occurs as Water and in Petroleum.

School laboratory Preparation

Procedure

Put Zinc granules in a round/flat/conical flask.

Add dilute sulphuric (VI) /Hydrochloric acid.

Add about 3cm3 of copper (II) sulphate (VI) solution.

Collect the gas produced over water as in the set up below.

Discard the first gas jar. Collect several gas jars.

Observation

Zinc reacts with dilute sulphuric (VI)/hydrochloric acid to form a salt and produce hydrogen gas.

When the acid comes into contact with the metal, there is rapid effervescence/ bubbles /fizzing are produced and a colourless gas is produced that is collected:

(i) Over water because it is insoluble in water

(ii) Through downward displacement of air/upward delivery because it is less dense than air.

The first gas jar is impure. It contains air that was present in the apparatus.

Copper (II) sulphate (VI) solution act as catalyst.

Chemical equation

(a) Zinc + Hydrochloric acid -> Zinc chloride + Hydrogen
Zn(s) + 2HCl (aq) -> ZnCl2 (aq) + H2 (g)

Ionic equation

Zn (s) + 2H+ (aq) -> Zn2+ (aq) + H2 (g)

Zinc + Sulphuric (VI) acid -> Zinc Sulphate (VI) + Hydrogen
Zn(s) + H2SO4 (aq) -> ZnSO4 (aq) + H2 (g)

Ionic

Zn (s) + 2H+ (aq) -> Zn2+ (aq) + H2 (g)

(b) Chemical equation

Magnesium + Hydrochloric acid -> Magnesium chloride + Hydrogen
Mg(s) + 2HCl (aq) -> MgCl2 (aq) + H2(g)

Ionic equation

Mg (s) + 2H+ (aq) -> Mg2+ (aq) + H2 (g)

Magnesium + Sulphuric (VI) acid -> Magnesium Sulphate(VI) + Hydrogen
Mg(s) + H2SO4 (aq) -> MgSO4 (aq) + H2(g)

Ionic equation

Mg (s) + 2H+(aq) -> Mg2+ (aq) + H2 (g)

(c) Chemical equation

Iron + Hydrochloric acid -> Iron (II) chloride + Hydrogen
Fe(s) + 2HCl (aq) -> FeCl2 (aq) + H2 (g)

Ionic equation

Fe (s) + 2H+(aq) -> Fe2 (aq) + H2 (g)

Iron + Sulphuric (VI) acid -> Iron (II) Sulphate (VI) + Hydrogen
Fe(s) + H2SO4 (aq) -> FeSO4 (aq) + H2 (g)

Ionic equation

Fe (s) + 2H+ (aq) -> Fe2+ (aq) + H2 (g)

Note:

1. Hydrogen cannot be prepared from reaction of

(i)Nitric (V) acid and a metal. Nitric (V) acid is a strong oxidizing agent. It oxidizes hydrogen gas to water.

(ii) Dilute sulphuric (VI) acid with calcium/Barium/Lead because Calcium sulphate (VI), Barium sulphate (VI) and Lead (II) sulphate (VI) salts formed are insoluble.

Once formed, they cover/coat the unreacted calcium/Barium/Lead stopping further reaction and producing very small amount/volume of hydrogen gas.

(iii) Dilute acid with sodium/potassium. The reaction is explosive.

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