Is a yellow non-metal, solid at room temp. It has two crystalline forms: rhombic and

monoclinic.

Produced by the burning of sulfur, it is used as a bleach in the manufacture of wood pulp for paper, and as a food preservative (antioxidant):

SO2(g) + 2H2O(l) H2SO3(aq)

SO2 and sulfites inhibit the growth of moulds, yeasts and aerobic bacteria.

They are also reductants and retard the oxidation of foods.

They are widely used in dried fruits, preserved meats and wine.

The Contact Process is used for the production of sulfuric acid.

1.Sulfur is burnt in air:

S(s) + O2(g) → SO2(g)

2. Then sulfur dioxide is heated with oxygen to 450°C in the presence of a vanadium (V) oxide (V2O5) catalyst, and turned into sulfur trioxide:

2SO2(g) + O2(g) ⇌ 2SO3(g) ∆H= -197 kJmol-1

3. Sulfur trioxide is dissolved in concentrated sulfuric acid to form oleum:

H2SO4(l) + SO3(g) → H2S2O7(l)

4. Oleum is added to water to form sulfuric acid:

H2S2O7(l) + H2O(l) → 2H2SO4(l)

Sulfuric acid is used in the production of many substances including soaps and detergents, paints/pigments, fertilisers, fibres and dyes

Concentrated sulfuric acid is used as a dehydrating agent (to remove water):

conc H2SO4

sucrose carbon + water

Even rain in clean environments has a pH of 5.5 – 6 due to naturally occurring CO2 and

oxides of nitrogen and sulfur.

In industrialised areas, with greater air pollution the pH can be as low as 4.0. This is called acid rain and is thought to be formed in the following sequence:

SO2(g) + NO2(g) SO3(g) + NO(g)

2NO(g) + O2(g) 2NO2(g)

The SO3 dissolves in water to form H2SO4 and the NO2 dissolves in water to form HNO3 thus:

SO3(g) + H2O(l) H2SO4(l)

2NO2(g) + H2O(l) + 1/2O2(g) 2HNO3(l)

Acid rain corrodes buildings made of marble and limestone.

It also corrodes metals.

When acid rain falls on soil, it can also cause aluminium ions and heavy metal ions to dissolve into water. Al3+ ions are toxic to many forms of aquatic life and heavy metal ions can cause damage to trees.