Translate the following statements into balanced chemical equations.
1. Hydrogen burns in the presence of air to form water.
2. Magnesium reacts with steam to form magnesium hydroxide and hydrogen gas.
3. Solution of barium chloride and sodium sulphate in water react to give insoluble barium sulphate and the solution of sodium chloride.
4. Dilute sulphuric acid reacts with aluminium powder.
5. Phosphorus reacts with chlorine to form phosphorus pentachloride.
6. Mercuric oxide is heated.
7. Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.
8. Zinc carbonate undergoes calcination.
9. Barium chloride reacts with zinc sulphate to give zinc chloride and barium sulphate as precipitate.
10. Aluminium + copper chloride → aluminium chloride + copper.
Please answer.
Answers
Answer:
Page No: 6
1. Why should a magnesium ribbon be cleaned before it is burnt in air?
Ans: Magnesium is an very reactive metal. When stored, it reacts with oxygen to form a layer of magnesium oxide on its surface. This layer of magnesium oxide is quite stable and prevents further reaction of magnesium with oxygen. The magnesium ribbon is cleaned by sand paper for removing this layer so that the underlying metal can be exposed to air.
2. Write the balanced equation for the following chemical reactions.
(a) Hydrogen + Chlorine → Hydrogen chloride
(b) Barium chloride + Aluminium sulphate → Barium sulphate + Aluminium chloride
(c) Sodium + Water → Sodium hydroxide + Hydrogen
Ans: (a) H2 (g) + Cl2 (g) → 2HCl (g)
(b) 3BaCl2 (s) + Al2(SO4)3 (s) → 3BaSO4(s) + 2AlCl3 (s)
(c) (c) 2Na(s) + 2H2O (l) → 2NaOH (aq) + H2 (g)
3. Write a balanced chemical equation with state symbols for the following reactions.
(a) Solutions of barium chloride and sodium sulphate in water react to give insoluble barium sulphate and the solution of sodium chloride.
(b) Sodium hydroxide solution (in water) reacts with hydrochloric acid solution (in water) to produce sodium chloride solution and water.
Ans: (a) BaCl2 (aq) + Na2SO4 (aq) → BaSO4 (s) + 2NaCl (aq)
(b) NaOH (aq) + HCl (aq) → NaCL (aq) + H2O (l)
Page No: 10
1. A solution of a substance ‘X’ is used for white washing.
(a) Name the substance ‘X’ and write its formula.
(b) Write the reaction of the substance ‘X’ named in (a) above with water.
Ans: (a) The substance ‘X’ is calcium oxide. Its chemical formula is CaO.
(b) Calcium oxide reacts vigorously with water to form calcium hydroxide (slaked lime).
CaO (s) + H2O (l) → Ca(OH)2 (aq)
Calcium Oxide (Quick Lime) + Water → Calcium Hydroxide (Slaked Lime)
2. Why is the amount of gas collected in one of the test tubes in Activity 1.7 double of the amount collected in the other? Name this gas.
Ans: Water contains two parts of hydrogen and one part oxygen. Therefore, during the electrolysis of water the amount of hydrogen gas collected in one of the test tubes is double than that of the oxygen produced and collected in the other test tube.
Page No: 13
1. Why does the colour of copper sulphate solution change when an iron nail is dipped in it?
Ans: When an iron nail dipped in the copper sulphate solution than iron displaces copper from the copper sulphate because iron is more reactive than copper. Therefore the colour of the copper sulphate solution changes.
The reaction involved here is:
Fe (s) + CuSO4 (aq) → FeSO4 (aq) + Cu (s)
2. Give an example of a double displacement reaction other than the one given in Activity 1.10.
Ans: 2KBr (aq) + BaI2 (aq) → 2KI (aq) + BaBr2 (aq)
3. Identify the substances that are oxidised and the substances that are reduced in the following reactions.
(a) 4Na (s) + O2 (g) → 2Na2O (s)
(b) CuO (s) + H2 (g) → Cu (s) + H2O (l)
Ans: (a) Sodium (Na) is oxidised as it gains oxygen and oxygen gets reduced.
(b) Copper oxide (CuO) is reduced to copper (Cu) while hydrogen (H2) gets oxidised to water (H2O).
Excercise
Page No: 14
1. Which of the statements about the reaction below are incorrect?
2PbO (s) + C (s) → 2Pb (s) + CO2 (g)
(a) Lead is getting reduced.
(b) Carbon dioxide is getting oxidised.
(c) Carbon is getting oxidised.
(d) Lead oxide is getting reduced.
(i) (a) and (b)
(ii) (a) and (c)
(iii) (a), (b) and (c)
(iv) all
Ans: (a) (a) and (b)
2. Fe2O3 + 2Al → Al2O3 + 2Fe
The above reaction is an example of a
(a) combination reaction.
(b) double displacement reaction.
(c) decomposition reaction.
(d) displacement reaction.
Ans: (d) displacement reaction.
Page No: 15
3. What happens when dilute hydrochloric acid is added to iron filings? Tick the correct answer.
(a) Hydrogen gas and iron chloride are produced.
(b) Chlorine gas and iron hydroxide are produced.
(c) No reaction takes place.
(d) Iron salt and water are produced.
Ans: (a) Hydrogen gas and iron chloride are produced.
4.
Ans: (a) 3H2 (g) + N2 (g) → 2NH3 (g)
(b) 2H2S (g) + 3O2 (g) → 2H2O (l) + 2SO2 (g)
(c) 3BaCl2 (aq) + Al2(SO4)3 (aq) → 2AlCl3 (aq) + 3BaSO4 (s)
(d) 2K (s) + 2H2O (l) → 2KOH (aq) + H2 (g)
6. Balance the following chemical equations.
(a) HNO3 + Ca(OH)2 → Ca(NO3)2 + H2O
(b) NaOH + H2SO4 → Na2SO4 + H2O
(c) NaCl + AgNO3 → AgCl + NaNO3
(d) BaCl2 + H2SO4 → BaSO4 + HCl
Ans: (a) 2HNO3 + Ca(OH)2 → Ca(NO3)2 + 2H2O
(b) 2NaOH + H2SO4 → Na2SO4 + 2H2O
(c) NaCl + AgNO3 → AgCl + NaNO3
(d) BaCl2 + H2SO4 → BaSO4 + 2HCl