WJEC Chemistry for AS Level Student Book: 2nd Edition

Worked example 2 When a solution of sodium hydroxide is added to a solution of magnesium chloride a white precipitate forms. The chemical equation for the reaction is: 2NaOH(aq) + MgCl 2 (aq) A 2NaCl(aq) + Mg(OH) 2 (s) Writing out all of the ions gives: 2Na + (aq) + 2OH − (aq) + Mg 2+ (aq) + 2Cl − (aq) A 2Na + (aq) + 2Cl − (aq) + Mg(OH) 2 (s) The Na + (aq) ions and the Cl − (aq) ions do not change during the reaction. They are spectator ions and can be omitted, giving the ionic equation: Mg 2+ (aq) + 2OH − (aq) A Mg(OH) 2 (s) Test yourself 1. Radium carbonate has the formula RaCO 3 . Write the formula of radium hydroxide. [1] 2. State the oxidation number of chromium in CrO 2 Cl 2 [1] 3. Magnetite ore can be reduced by carbon monoxide in a blast furnace to produce iron as part of steel production. Balance the equation for the reduction of magnetite. Fe 3 O 4 + CO A Fe + CO 2 [1] 4. When ethanol, C 2 H 5 OH, is burnt in air, the only products are carbon dioxide and water. Balance the equation for this reaction. C 2 H 5 OH + O 2 A CO 2 + H 2 O [1] 5. When calcium is added to cold water, calcium hydroxide and hydrogen form. Write the balanced chemical equation for this reaction. [1] 6. Write a balanced equation for the reaction between SiCl 4 and water to form SiO 2 and HCl only. [1] 7. Lead phosphate is precipitated when aqueous ammonium phosphate is mixed with aqueous lead nitrate. Write the balanced chemical equation for this reaction. [1] 8. An oxide of nitrogen reacts with water to form nitric acid as one of the products: NO 2 (g) + H 2 O(l) A HNO 3 (g) + NO(g) (a) Balance the equation above. [1] (b) Give the oxidation numbers of nitrogen in all three nitrogen species. [2] 9. When an aqueous solution of calcium hydroxide is added to an aqueous solution of sodium carbonate a white precipitate of calcium carbonate is seen. Write the ionic equation for this reaction. Include the relevant state symbols in the equation. [1] Link Solubility of Group 2 cations page 69. 1.1 Formulae and equations 15