 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): SO 2(g) + 2H 2 O(l)  H 2 SO 3(aq)  SO 2 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) + O 2(g) → SO 2(g)

2. Then sulfur dioxide is heated with oxygen to 450°C in the presence of a vanadium (V) oxide (V 2 O 5 ) catalyst, and turned into sulfur trioxide: 2SO 2(g) + O 2(g) ⇌ 2 SO 3(g) ∆ H= -197 kJmol Sulfur trioxide is dissolved in concentrated sulfuric acid to form oleum: H 2 SO 4(l) + SO 3(g) → H 2 S 2 O 7(l) 4. Oleum is added to water to form sulfuric acid: H 2 S 2 O 7(l) + H 2 O (l) → 2H 2 SO 4(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 H 2 SO 4 sucrose  carbon + water

 Even rain in clean environments has a pH of 5.5 – 6 due to naturally occurring CO 2 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: SO 2(g) + NO 2(g)  SO 3(g) + NO (g) 2NO (g) + O 2(g)  2NO 2(g)  The SO 3 dissolves in water to form H 2 SO 4 and the NO 2 dissolves in water to form HNO 3 thus: SO 3(g) + H 2 O (l)  H 2 SO 4(l) 2NO 2(g) + H 2 O (l) + 1 / 2 O 2(g)  2HNO 3(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. Al 3+ ions are toxic to many forms of aquatic life and heavy metal ions can cause damage to trees.