Sulfur and Carbonates

Question 1

Name 4 sources of sulphur

Answer 1

1. Found as an element in underground sulphur beds
2. Found around the rims of volcanoes
3. Compound in metal ores, e.g. zine blende (ZnS) and galena (PbS)
4. Compounds in fossil fuels

Question 2

Describe how sulphur is extracted from

1. natural gas
2. underground sulpur beds

Answer 2

1. natural gas can have as much as 30% hydrogen sulphide, which is separated from methane and reacted with oxygen using a catalyst
   
   • 2H₂S_(g) + O_2(g) → 2S_(s) + 2H₂O_(l)
2. Heated water is pumped down to melt the sulphur and carry it to the surface (m.p. is 115^oC)

Question 3

List 8 properties of sulphur

Answer 3

1. Brittle
2. Yellow solid at r.t.p.
3. Two allotropes: rhombic sulphur at r.t.p., monoclinic sulphur when slowly heated above 96^oC
4. Low m.p. and b.p.
5. Does not conduct electricity
6. Insoluble in water
7. Reacts with metals to form sulphides
8. Burns in oxygen to form sulphur dioxide
   
   • S_(s) + O_2(g) → SO_2(g)

Question 4

List some uses of sulphur

Answer 4

• Mostly used to make sulphuric acid
• Vulcanising - added to rubber to toughen it
• Making drugs, pesticides, dyes, matches, paper, cosmetics, shampoos and body lotions
• Added to cement to make sulphur concrete (which is not attacked by acid, so is used in factories that use acid)

Question 5

List 4 properties of sulphur dioxide

Answer 5

1. Colourless gas heavier than air, with a strong, choking smell
2. Acidic oxide that dissolves in water to form sulphurous acid, that breaks down easily
   
   • H₂O_(l) + SO_2(g) → H₂SO_3(aq)
3. Acts as a bleach when damp or in solution, as it reduces coloured compounds to remove the colour
4. Can kill bacteria

Question 6

List 3 uses of sulphur dioxide

Answer 6

1. Manufacting sulphuric acid
2. Bleaching wool, silk, and wood pulp for paper
3. Food preservative

Question 7

Describe the steps of the Contact process

Answer 7

1. Sulphur burned in air to form sulphur dioxide
   
   • S_(s) + O_2(g) → SO_2(g)
2. Mixed with more air to make sulphur trioxide
   
   • 2SO_2(s) + O_2(g) → 2SO_3(g)
   • 450^oC at 2atm
   • four beds of vanadium(V) oxide catalyst
   • forward reaction is exothermic
   • SO₃ removed between last two beds to increase yield
3. Dissolved in concentrated sulphuric acid to form a thick fuming liquid called oleum
   
   • SO_3(g) + H₂SO_4(l) → H₂S₂H_7(l)
   • Adding directly to water is too exothermic and a thick, dangerous mist of acid forms
4. Mixed carefully with water to form concentrated sulphuric acid

Question 8

List 5 main uses of sulphuric acid

Answer 8

1. fertilisers, e.g. ammonium sulphate
2. paints, pigments, and dyes
3. fibres and plastics
4. soaps and detergents
5. acid in car batteries

Question 9

Describe the properties of sulphuric acid

Answer 9

• Forms salts called sulphates
• When concentrated, it’s a dehydrating agent, and a thick oily liquid
• Turns blue litmus red
• Dilute acid made by adding concentrated acid to water, not the other way around (too exothermic)
• Typical acid reactions
• Strong acid: low pH, high conductivity