Question

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.

Answer 1

double displacement reaction with formation of white precipitate
Na2SO4 +BaCl 2 will become BaSO4 +NaCl

Answer 2

2Na +2H₂O ---------> 2NaOH + H₂