important question, class 10, science, part – 3

  1. (a) What is the colour of ferrous sulphate crystals? How does this colour change after heating?  (b) Name the products formed on strongly heating ferrous sulphate crystals. What type of chemical reaction occurs in this change?  (Delhi 2009)
  2. What is an oxidation reaction? Give an example of oxidation reaction. Is oxidation an exothermic or an endothermic reaction?    (Delhi 2009)
  3. What is observed when a solution of potassium iodide is added to a solution of lead nitrate taken in a test tube?
  4. What is an oxidation reaction? Identify in the following reaction; (Delhi 2008) ZnO +C….Zn + CO (i) the substance oxidised and (ii) the substance reduced.
  5. A solution of a substance X, is used for white washing. (i) Name the substance X, and write its formula. (ii) Write the reaction of the of the substance X, named in (i) above with water      (HOTS)
  6. Write a balanced chemical equation with state symbols for the following reactions. (i) Solutions of barium chloride and sodium sulphatein water react to give insoluble barium sulphate and the solution of sodium chloride(ii) Sodium hydroxide solution (in water) reacts with hydrochloric acid solution (in water) to produce sodium chloride and water.
  7. Translate the following statements into chemicals equations and then balance them; (a) Hydrogen gas combines with nitrogen to from ammonia. (b) Hydrogen sulphide gas burns in air to give water and sulphur dioxide. (c) Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate of barium sulphate.(d) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.
  8. What do you mean by exothermic and endothermic reactions? Give examples.
  9. What do you mean by a precipitation reaction? Explain giving examples?
  10. A shiny brown coloured element X, on heating in air becomes black in colour. Name the element X, and the black coloured compound formed.
  11. Why do we apply paint on iron articles?
  12. In the refining of silver, the recovery of silver from silver nitrate solution involved displacement by copper metal. Write down the reaction involved.
  13. A metal nitrate A, on heating gives yellowish brown coloured metal oxide along with brown gas B, and a colourless gas C, . Aqueous solution of A, on reaction with potassium iodide forms a yellow precipitate of compound D, . Identify A,B,C,D,. Identify the types of both the reactions.Metal present in A, is used in alloy which is used for soldering purposes.(HOTS)
  14. Why do fire flies glow at night?
  1. Which among the following are physical or chemical changes? (a) Evaporation of petrol (b) Burning of Liquefied petroleum Gas (LPG) (c) Heating of an iron rod to red hot (d) Curding of milk (e) Sublimation of solid ammonium chloride.
  2. Write a balanced chemical equation for each of the following reactions and also classify them. (a) Lead acetate solution is treated with dilute hydrochloric acid to form lead chloride and acetic acid solution.(b) A piece of sodium metal is added to absolute ethanol to form sodium Ethoxide  and hydrogen gas.(c) Iron (III) oxide on heating with carbon monoxide gas reacts to form solid iron and liberates carbon dioxide gas.(d) Hydrogen sulphide gas reacts with oxygen gas to form solid sulphur and liquid water.
  3. Why do we store silver chloride in dark coloured bottles?
  4. What happens when a piece of (a) Zinc metal is added to copper sulphate solution?  (b) Aluminium metal is added to dilute hydrochloric acid? (c) Silver metal is added to copper sulphate solution?
  5. A magnesium ribbon is burnt in oxygen to give a white compound X accompanied by emission of light. If the burning ribbon is now placed in an atmosphere of nitrogen. It continues to burn and forms a compound Y. (a) Write the chemical formula of X and Y. (b) Write a balanced chemical equation, when X is dissolved in water.    (HOTS)
  6. A silver article generally turns black when kept in the open for a few days. The article when rubbed with toothpaste again starts shining. (HOTS) (a) Why do silver articles turn black when kept in the open for a few days? Name the phenomenon involved. (b) Named the black substance formed and give its chemical formula.
  7. What happens when Zinc granules are treated with dilute solution of H2SO4, HCL, HNO3, NaCL and NaCL and NaOH, also write the chemical equations if reaction occurs.  (HOTS)