(i) Mercury is liquid at room temperature.
(ii) Sodium can be easily cut with a knife.
(iii) Silver is the best conductor of heat.
(iv) Lead is a poor conductor of heat.
Malleable means a substance can be beaten into thin sheets. Ductile means it can be drawn into thin wires. Metals generally show both these properties.
Sodium is very reactive and reacts vigorously with oxygen and moisture in air, producing heat and possibly catching fire. It is kept under kerosene oil to prevent contact with air and water.
(i) 3Fe + 4H₂O(g) → Fe₃O₄ + 4H₂
(ii) Ca + 2H₂O → Ca(OH)₂ + H₂; 2K + 2H₂O → 2KOH + H₂
From the displacement results, B is the most reactive metal because it displaces iron from iron(II) sulphate.
(i) Most reactive metal: B.
(ii) B will displace copper from copper(II) sulphate solution, so copper will be deposited and the blue colour will fade.
(iii) Decreasing reactivity: B > A > C > D.
Hydrogen gas is produced. Iron reacts with dilute sulphuric acid to form iron(II) sulphate and hydrogen: Fe + H₂SO₄ → FeSO₄ + H₂.
Zinc is more reactive than iron, so it displaces iron from iron(II) sulphate. The pale green colour of FeSO₄ fades and iron is deposited. Zn + FeSO₄ → ZnSO₄ + Fe.
(i) Sodium has one valence electron (Na·), oxygen has six valence electrons, and magnesium has two valence electrons (Mg with two dots).
(ii) In Na₂O, each of two Na atoms loses one electron to oxygen: 2Na → 2Na⁺ + 2e⁻; O + 2e⁻ → O²⁻. In MgO, Mg loses two electrons to oxygen: Mg → Mg²⁺ + 2e⁻; O + 2e⁻ → O²⁻.
(iii) Ions present are Na⁺ and O²⁻ in Na₂O; Mg²⁺ and O²⁻ in MgO.
Ionic compounds contain oppositely charged ions held together by strong electrostatic forces in a crystal lattice. A large amount of energy is required to overcome these forces, so they have high melting points.
(i) A mineral is an element or compound that occurs naturally in the earth's crust.
(ii) An ore is a mineral that contains a high percentage of a metal from which the metal can be profitably extracted.
(iii) Gangue is the earthy impurity such as sand or soil associated with an ore.
Gold and platinum are found in nature in the free state because they are very unreactive.
Reduction is used for obtaining a metal from its oxide. The metal oxide is reduced to the metal by removing oxygen, often with carbon, carbon monoxide or a more reactive metal.
A displacement reaction occurs when a more reactive metal reduces the oxide of a less reactive metal. With zinc, magnesium and copper, magnesium is most reactive, zinc is next and copper is least reactive. Therefore magnesium displaces zinc and copper from their oxides, and zinc displaces copper from copper oxide. Copper does not displace zinc or magnesium.
Unreactive metals such as gold and platinum do not corrode easily.
Alloys are homogeneous mixtures of two or more metals, or of a metal and a non-metal. Examples include brass, bronze and steel.
- a. NaCl solution and copper metal
- b. MgCl₂ solution and aluminium metal
- c. FeSO₄ solution and silver metal
- d. AgNO₃ solution and copper metal.
Copper is more reactive than silver, so it displaces silver from silver nitrate solution.
(d) AgNO₃ solution and copper metal.
- a. Applying grease
- b. Applying paint
- c. Applying a coating of zinc
- d. All of the above.
For a frying pan, grease and paint would burn or contaminate food. Zinc coating prevents rusting by galvanisation.
(c) Applying a coating of zinc
- a. calcium
- b. carbon
- c. silicon
- d. iron.
Calcium forms ionic calcium oxide, which has a high melting point and reacts/dissolves in water to form calcium hydroxide.
(a) calcium
- a. zinc is costlier than tin.
- b. zinc has a higher melting point than tin.
- c. zinc is more reactive than tin.
- d. zinc is less reactive than tin.
Zinc is more reactive and can react with food acids, making food unsafe. Tin is less reactive and safer for coating food cans.
(c) zinc is more reactive than tin.
(a) Beat each sample gently with a hammer. Metals flatten into sheets because they are malleable; non-metals usually break. Then connect each sample in a circuit with the battery, bulb, wires and switch. Metals conduct electricity and make the bulb glow; most non-metals do not.
(b) These tests are useful but not perfect. Some metals are brittle, and graphite, a non-metal, conducts electricity.
Amphoteric oxides are oxides that react with both acids and bases to form salt and water. Examples: aluminium oxide (Al₂O₃) and zinc oxide (ZnO).
Metals above hydrogen in the reactivity series, such as zinc and iron, displace hydrogen from dilute acids. Metals below hydrogen, such as copper and silver, do not.
In electrolytic refining, the impure metal M is made the anode, a thin strip of pure metal M is made the cathode, and a solution of a soluble salt of metal M is used as the electrolyte.
Burning sulphur forms sulphur dioxide.
(a) (i) Dry litmus paper shows no change because SO₂ needs water to show acidic character. (ii) Moist blue litmus turns red because sulphurous acid is formed.
(b) S + O₂ → SO₂; and in water, SO₂ + H₂O → H₂SO₃.
Rusting of iron can be prevented by painting/oiling/greasing the surface to keep air and moisture away, and by galvanising it with a coating of zinc.
Non-metals generally form acidic oxides when they combine with oxygen, such as CO₂ and SO₂. Some non-metal oxides are neutral, such as CO and NO.
(a) Platinum, gold and silver are lustrous, malleable and resistant to corrosion, so they remain attractive as jewellery.
(b) Sodium, potassium and lithium react vigorously with air and water, so they are stored under oil to prevent contact.
(c) Aluminium forms a thin protective oxide layer that prevents further corrosion; it is also light and a good conductor of heat.
(d) Metals are easier to reduce from oxides than from carbonates or sulphides, so ores are first converted to oxides by calcination or roasting.
Tarnished copper has a green coating of basic copper carbonate. Lemon and tamarind contain acids, which react with and dissolve this basic coating, exposing the shiny copper surface.
Metals usually lose electrons to form positive ions, while non-metals gain or share electrons to form negative ions or covalent compounds. Metals form basic or amphoteric oxides; non-metals generally form acidic oxides. Metals react with dilute acids to produce hydrogen gas if they are above hydrogen in the reactivity series; non-metals generally do not. Metals form ionic chlorides such as NaCl, while non-metals often form covalent chlorides such as CCl₄.
He used aqua regia, a freshly prepared mixture of concentrated hydrochloric acid and concentrated nitric acid in the ratio 3:1. Aqua regia dissolves gold, so a thin layer of the gold bangles dissolved, making them look shiny but reducing their weight.
Copper is less reactive than iron and does not react with hot water or steam easily. Steel contains iron, which can corrode in contact with hot water and steam. Hence copper is preferred for hot water tanks.