Thursday, September 8, 2011

Important Questions CBSE CLASS X Science (Chemical Reaction)

1. Write a chemical equation for each of the following reactions (2 marks)
(i) Zinc metal reacts with aqueous solution of hydrochloric acid to form zinc chloride solution and hydrogen gas.
(ii) When solid mercury (II) oxide is heated, liquid mercury and oxygen gas are produced.
2. Give two examples from daily life where redox reactions are taking place. (2 marks)
3. State any two methods to prevent or retard the development of rancidity in fat and oil containing foods. (2 marks)
4. Why articles made of aluminium do not corrode? (2 marks)
5. Giving examples explain the difference between balanced and unbalanced chemical equations. (2 marks)
8. What is the difference between displacement and double displacement reactions? Write equations for these reactions. (3 marks)
9. What are the three essentials of a chemical equation? (3 marks)
10. What is corrosion? What are its effects? State two conditions necessary for the rusting of iron. (3 marks)
11. (i) What is meant by ‘oxidation’ in terms of oxygen?  (ii) In the reaction represented by the equation:
MnO2 + 4HCI ---------------_ MnCI2 + 2H2O + CI2
(a) Name the substance oxidized (b) Name the oxidizing agent  (c ) Name the substance reduced (d) Name the reducing agent. (5 marks)         Or
Write one activity to show the decomposition of a chemical compound with the evolution of a gas.
12. (i) Explain the term ‘corrosion’ with an example.  (ii) Which chemical reaction is involved in the corrosion of iron?   (iv) Name any two objects (or structures) which are gradually damaged by the corrosion of iron and steel?
(v) Name two metals which corrode easily and two metals which do not corrode easily.
(vi) Aluminium corrodes in moist air but it is widely used for making cooking vessels and other cutlery. Explain. (5 marks)
13. Give reasons for the following –
  1. Keeping food in air tight containers help in preventing rancidity. 
  2. Moist air and acidic gases are not good for some metals. 
  3. White coloured silver chloride turns grey when kept in sunlight. 
  4. Decomposition reaction called the opposite of combination reaction. 
  5. Can a displacement be a redox reaction? 
  6. Corrosion of aluminium is considered to be advantageous. 
  7. Hydrogen peroxide is kept in coloured bottles. 
  8. Quick lime is used in whitewashing the walls. 
  9. Respiration is considered an exothermic process. 
  10. We cannot stir silver nitrate solution with copper spoon. 
  11. Gold and platinum do not get affected even if there is a presence of moist air and acidic gases.   
  12. 13. Five metals A, B, C, D and F are added to the following solutions one by one. The observations made are below :
Iron(II) sulphate
Copper(II) sulphate
Zinc sulphate
Silver nitrate
Aluminium sulphate
No reaction
Reddish brown deposit
Coating on it
Coating on it
Grey deposit
No reaction
Coating on it
No reaction
No reaction
No reaction
White deposit
No reaction
No reaction
No reaction
No reaction
No reaction
Reddish brown deposit
New coating
New coating
No reaction
Answer the following questions based on above observations-
  1. Which is the most active metal and which is the least reactive? Why?
  2. What would be observed when (a).  B is added to a solution of copper (II) sulphate and   (b). E is added to the solution of iron sulphate? Explain, why?
  3. Arrange the metals A, B, C, D and E in order of increasing reactivity.
  4. Container of which metal can be used to store both zinc sulphate solution and silver nitrate solution.
  5. Which of the above solutions can be easily stored in a container made up of these metals?
  1. Identify the type of chemical reaction taking place in each of the following–
  1. Barium chloride solution is mixed with copper sulphate solution and a white precipitate is formed.
  2. On heating copper powder in air in a china dish, the surface of the copper powder turns black.
  3. On heating green coloured sulphate crystals, reddish brown solid is left and smell of gas having odour of burning sulphur is experienced.
  4. White silver chloride turns grey in sunlight.
  5. Barium hydroxide reacts with ammonium chloride solution to give ammonia, barium chloride and water.
  6. Iron nails when left dipped in blue copper sulphate solution become brownish in colour and the blue colour of copper sulphate fades away.
  7. Quick lime reacts vigorously producing a hissing sound with water releasing a large amount of heat.

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