35. What happens when sodium sulphate and barium chloride solutions are mixed together ? Write reaction with observation. 36. An aluminium can is used to store ferrous sulphate solution. It is observed that in a few days holes appeared in the can. Explain the cause for this observation and write chemical equation to support your answer. 37. Why is photosynthesis considered an endothermic reaction ? 38. A few drops of sulphuric acid are added into water before electrolysis. Why ? 39. Balance the following chemical equations : (i) BaCl2 +H2SO4BaSO4+HCl (ii) Ca(OH)2+HNO3Ca(NO3)2+H2O (iii) Pb(NO3)2 PbO+NO2+O2 (iv) MnO2+HClMnCl2+H2O+Cl2 40. State the chemical change that takes place when lime stone is heated strongly. 41. An element ‘X’ on reaction with dilute acid evolves a gas that burns with a pop sound, while a compound ‘Y’ on reaction with dilute acid evolves a gas that turns lime water milky. Identify X and Y. 42. A copper coin was kept dipped in AgNO3 solution for few hours, as shown in the figure. What will happen to the : (a) copper coin’ (b) colour of the solution ? 43. A solution of potassium chloride when mixed with silver nitrate solution, an insoluble white substance is formed. Write the chemical reaction involved and also mention the type of the chemical reaction ? 44. A white salt on heating decomposes to give brown fumes and a residue is left behind. (i) Name the salt. (ii) Write the equation for the decomposition reaction. 45. Which one is a chemical change- rusting of iron or melting of iron ? 46. Why do silver articles become black after some time when exposed to air? 47. (a) If an iron nail is immersed in the aqueous solution of copper sulphate, what are the changes happening to the nail and to the solution? (b) Write the balanced chemical equation for the reaction between iron metal and aqueous copper sulphate solution. 48. Give an example each for thermal decomposition and photo chemical decomposition reactions. Write relevant balanced chemical equations also. 49. (a) Oil and fat containing food items are flushed with nitrogen while packing them why ? (b) Why do we apply paint on iron articles ? 50. What would you observe when. (i) calcium oxide is added to water ? (ii) barium chloride solution is added to sodium sulphate solution ? Write the reaction involved in each case.
Answers
35-When barium chloride combines with sodium sulphate in the form of their aqueous solutions, a white precipitate of barium sulphate is formed which is insoluble in water. The reaction also creates sodium chloride, which remains dissolved in water and so cannot be seen. ... So this reaction is a chemical change.
36-It is a displacement reaction. Aluminium is more reactive than iron. So, Fe is displaced by Al and aluminium sulphate is formed and iron is precipitated.
3FeSO4 + 2Al → Al2(SO4)3 + 3Fe
37-Unlike many other endothermic reactions, photosynthesis does not absorb energy as heat. Instead, during plants absorb energy from sunlight to turn carbon dioxide and water into oxygen and glucose, which is a type of sugar molecule. The energy is stored in the glucose molecules, ready to be used when needed.
38-A few drops of sulphuric acid are added into water before electrolysis. ... To increase the conductivity of water a few drops of sulphuric acid is added .Being a strong acid it can ionize completely to release H+ ions. These H+ ions are responsible for the conduction of electricity.
39-(i) BaCl2 + H2SO4 → BaSO4 + 2HCl
(ii) Ca(OH)2 + 2HNO3 → Ca(NO3)2 + 2H2O
(iii) 2Pb(NO3)2 → 2PbO + 4NO2 + O2
(iv) MnO2 + 4HCl → MnCl2 + 2H2O + Cl2
40-Decomposition reaction is the chemical change that takes place when limestone is heated strongly. As a result quick lime and Carbon dioxide is formed. When Lime Stone is heated quick lime and Carbon dioxide is formed.
41-Here element X can be any metal as metals reacts with acid to form salt and produce hydrogen gas which burns with a pop sound. ... Here the compound Y is any metal carbonate or metal bicarbonate which reacts with dil. HCl to form salt, water and CO2 gas is evolved.
42-Copper metal is more reactive than silver metal thus, when copper coin is kept immersed in silver nitrate solution for some time, it displaces silver from silver nitrate solution. The grey solid crystal of Ag metal are seen growing on the copper coin and solution turns blue in colour.
43-KCl(aq) + AgNO3(aq) → AgCl(s) + KNO3(aq)
It is a double displacement and precipitation reaction.
44-A white salt on heating decomposes to give brown fumes and yellow residue.Name the salt and write the reaction. ... The chemical name of white salt is Lead nitrate Pb(NO3)2. The salt on heating produces brown fumes. This implies that the salt contains nitrate ion.
45- Which one is a chemical change, the rusting of iron or the melting of iron? The rusting of ion is a chemical change because the iron atoms form chemical bonds with the oxygen atoms to form iron oxide molecules.
46-Silver articles, when exposed to air become black after sometime. This is because the silver metal reacts with sulphur present in the atmosphere and forms silver sulphide. Thus, a layer of silver sulphide is formed on the surface of silver articles, because of which they appear dull and black.
47- (a) When an iron nail is immersed in the aqueous solution of copper sulphate, a brown coating of copper is developed over iron and the blue copper sulphate solution becomes pale green since iron is more reactive than copper. (c) It is a chemical change and the above reaction is a displacement reaction.
(b) CuSO4•5H2O + Fe = FeSO4•H2O + Cu + 4H2O(l)
Change in Free Energy: ΔG(20C) = -147.3kJ (negative, so the reaction runs)
Change in Enthalpy: ΔH(20C) = -106.4kJ (negative, so the reaction is exothermic)
49-(i) begin mathsize 12px style CaCO subscript 3 left parenthesis straight s right parenthesis end subscript space rightwards arrow with increment on top space CaO subscript left parenthesis straight s right parenthesis end subscript space plus CO subscript 2 left parenthesis straight s right parenthesis end subscript end style (Thermal decomposition)
(ii)begin mathsize 12px style 2 AgBr subscript left parenthesis straight s right parenthesis end subscript space rightwards arrow with Sunlight on top space 2 Ag subscript left parenthesis straight s right parenthesis end subscript space plus Br subscript 2 left parenthesis straight g right parenthesis end subscript end style (photochemical decomposition)