nd Chemistry Matters for GCE ‘O’ Level (2 Edition): Full Solutions to Textbook Questions Chapter 4 Chapter 4 Elements, Compounds and Mixtures Test Yourself 4.1 (page 65) 1. (a) Mg and Mn (b) S and Si (c) Zn and Sn 2. Poor conductor of heat Dull looking Brittle 3. Ductile and malleable Good conductor of electricity Solid at r.t.p. Test Yourself 4.2 (page 69) 1. (a) AlF3: aluminium, fluorine Co: cobalt CoO: cobalt, oxygen CO: carbon, oxygen CaSO4: calcium, sulfur, oxygen Cu: copper (b) 2. (a) (b) (c) (d) (e) (f) Elements Co Compounds AlF3 Cu CoO CO CaSO4 N:H=1:3 Ca : Cl = 1 : 2 H:N:O=1:1:3 C:O:N:H=1:1:2:4 Na : O : H = 1 : 1 : 1 Cu : S : O = 1 : 1 : 4 Test Yourself 4.3 (page 71) 1. (a) B — Oxygen, O2 is diatomic and consists of the same type of molecules. Diagram B is the only diagram that represents a single element. (b) C — Cl2 and O2 are diatomic elements, therefore there will be two types of molecules in the mixture. Diagram C represents two diatomic elements. (c) A — Ammonia (NH3) and carbon dioxide (CO2) are compounds, each containing two types of atoms. Diagram A represents two compounds. © 2013 Marshall Cavendish International (Singapore) Private Limited 4.1 nd Chemistry Matters for GCE ‘O’ Level (2 Edition): Full Solutions to Textbook Questions Chapter 4 2. Elements bromine gold dust Compounds distilled water magnesium chloride Mixtures duralumin ink honey 3. Melting and boiling points — A mixture will melt or boil over a range of temperature whereas a pure compound or element has a fixed melting or boiling point. (Alternative answer: Solubility in water — Since the bonding in compounds is different from the bonding in elements, the solubility of compounds and elements in water will also be different.) Get it Right (page 73) (a) (b) (c) (d) (e) False. Mercury cannot be broken down into simpler substances. False. The symbol of an element may consist of one or two letters. False. Compounds can be made up of molecules or ions. True True Let’s Review (pages 73–74) Section A: Multiple-Choice Questions 1. A 2. A 3. A 4. D 5. C Section B: Structured Questions 1. (a) (b) (c) (d) (e) True True False. The elements present are nitrogen, hydrogen, oxygen and carbon. False. Urea is a compound; the elements are chemically combined. False. Carbon monoxide is a compound containing only one oxygen atom chemically combined to one carbon atom. Although an oxygen atom is chemically combined with a carbon atom in the urea molecule, there are also other atoms that are chemically combined with carbon. (f) True 2. (a) (b) (c) (d) (e) Brass Mud and syrup Air Wine Carbonated drink Section C: Free-Response Question 1. (a) Add xylene to the mixture. Stir until all the yellow solid (sulfur) had dissolved (add more xylene if necessary). Filter the resulting mixture. Sulfur is left in the filtrate. Wash the residue (blue-grey solid) with more xylene and leave residue to dry. (b) The mass ratio of Cu : S is 4 : 1. (c) 1. Energy change occurred when the blue-grey solid was formed – reaction was glowing red hot. 2. The compound formed had a fixed composition. 3. The compound formed had different properties from the starting materials (the compound was not removed by xylene, sulfur was removed by xylene). © 2013 Marshall Cavendish International (Singapore) Private Limited 4.2
