19. Write the balanced chemical equations for the following reactions and identify the type of reaction in each case.
(a) Nitrogen gas is treated with hydrogen gas in the presence of a catalyst at 773K to form ammonia gas.
(b) Sodium hydroxide solution is treated with acetic acid to form sodium acetate and water.
(c) Ethanol is warmed with ethanoic acid to form ethyl acetate in the presence of concentrated \(H_2SO_4\).
(d) Ethene is burnt in the presence of oxygen to form carbon dioxide, water and releases heat and light.
20. Write the balanced chemical equations for the following reactions and identify the type of reaction in each case.
(a) Thermit reaction, iron (III) oxide reacts with aluminium and gives molten iron and aluminium oxide.
(b) Magnesium ribbon is burnt in an atmosphere of nitrogen gas to form solid magnesium nitride.
(c) Chlorine gas is passed in an aqueous potassium iodide solution to form potassium chloride solution and solid iodine.
(d) Ethanol is burnt in air to form carbon dioxide, water and releases heat.
21. Complete the missing components/variables given as x and y in the following reactions:
(a) \(Pb(NO_3)_2(aq) + 2KI(aq) \to PbI_2(x) + 2KNO_3(y)\)
(b) \(Cu(s) + 2AgNO_3(aq) \to Cu(NO_3)_2(aq) + x(s)\)
(c) \(Zn(s) + H_2SO_4(aq) \to ZnSO_4(x) + H_2(y)\)
(d) \(CaCO_3(s) \xrightarrow{x} CaO(s) + CO_2(g)\)
22. Which among the following changes are exothermic or endothermic in nature?
(a) Decomposition of ferrous sulphate
(b) Dilution of sulphuric acid
(c) Dissolution of sodium hydroxide in water
(d) Dissolution of ammonium chloride in water
23. Identify the reducing agent in the following reactions:
(a) \(4NH_3 + 5O_2 \to 4NO + 6H_2O\)
(b) \(H_2O + F_2 \to HF + HOF\)
(c) \(Fe_2O_3 + 3CO \to 2Fe + 3CO_2\)
(d) \(2H_2 + O_2 \to 2H_2O\)
24. Identify the oxidising agent (oxidant) in the following reactions:
(a) \(Pb_3O_4 + 8HCl \rightarrow 3PbCl_2 + Cl_2 + 4H_2O\)
(b) \(2Mg + O_2 \rightarrow 2MgO\)
(c) \(CuSO_4 + Zn \rightarrow Cu + ZnSO_4\)
(d) \(V_2O_5 + 5Ca \rightarrow 2V + 5CaO\)
(e) \(3Fe + 4H_2O \rightarrow Fe_3O_4 + 4H_2\)
(f) \(CuO + H_2 \rightarrow Cu + H_2O\)
25. Write the balanced chemical equations for the following reactions:
(a) Sodium carbonate with hydrochloric acid (equal molar) gives sodium chloride and sodium hydrogencarbonate.
(b) Sodium hydrogencarbonate with hydrochloric acid gives sodium chloride, water and carbon dioxide.
(c) Copper sulphate on treatment with potassium iodide precipitates cuprous iodide (\(Cu_2I_2\)), liberates iodine gas and also forms potassium sulphate.
26. Potassium chloride solution mixed with silver nitrate solution gives an insoluble white substance. Write the chemical reaction and mention its type.
27. Ferrous sulphate decomposes with evolution of a gas having the odour of burning sulphur. Write the reaction and identify the type.
Why do fireflies glow at night?
29. Grapes on the plant do not ferment, but after plucking they can. Under what conditions do they ferment? Is it a chemical or a physical change?
30. Which among the following are physical or chemical changes?
(a) Evaporation of petrol (b) Burning of LPG (c) Heating an iron rod to red hot (d) Curdling of milk (e) Sublimation of solid ammonium chloride
31. During reactions of some metals with dilute HCl the following were observed. Explain with reasons:
(a) Silver metal does not show any change.
(b) Temperature of mixture rises when aluminium is added.
(c) Sodium metal reaction is highly explosive.
(d) Bubbles are seen when lead is reacted with the acid.
32. A substance X, an oxide of a group 2 element used in cement industry and present in bones, forms a solution turning red litmus blue on treatment with water. Identify X and write the reactions.
33. Write a balanced chemical equation for each reaction and classify them.
(a) Lead acetate solution with dilute HCl → lead chloride and acetic acid.
(b) Sodium metal added to absolute ethanol → sodium ethoxide and hydrogen gas.
(c) Iron(III) oxide heated with carbon monoxide → iron and carbon dioxide.
(d) Hydrogen sulphide reacts with oxygen gas → solid sulphur and liquid water.
Why is silver chloride stored in dark coloured bottles?
35. Balance the following equations and identify the type of reaction.
(a) \(Mg + Cl_2 \rightarrow MgCl_2\)
(b) \(HgO \xrightarrow{Heat} Hg + O_2\)
(c) \(Na + S \xrightarrow{Fuse} Na_2S\)
(d) \(TiCl_4(l) + Mg(s) \rightarrow Ti(s) + MgCl_2(s)\)
(e) \(CaO(s) + SiO_2(s) \rightarrow CaSiO_3(s)\)
(f) \(H_2O_2(l) \xrightarrow{UV} H_2O(l) + O_2(g)\)
36. A magnesium ribbon burns in oxygen to give a white compound X with light. In nitrogen it continues to burn forming Y.
(a) Write the formulae of X and Y.
(b) Write a balanced equation when X is dissolved in water.
Zinc liberates hydrogen with dilute HCl whereas copper does not. Explain.
38. A silver article turns black after a few days in open air and regains shine on rubbing with toothpaste.
(a) Why does it turn black? Name the phenomenon.
(b) Name the black substance formed and give its chemical formula.