Available Answers

1. 1.

   Fill in the blank spaces by choosing the correct words from the list given below :

   List : liquid, hydrogen sulphide, exothermic, yellow, dirty green

   1. When quick lime is placed in water an _____________ reaction takes and the reaction mixture gets very hot.
   2. When red hot coke (solid state), reacts with sulphur vapour the product, carbon disulphide is in _____________ state.
   3. Ferrous sulphate solution reacts with sodium hydroxide solution to form a _____________ precipitate of ferrous hydroxide.
   4. Lead nitrate crystals on heating strongly leave behind a solid residue, which is in _____________ colour.
   5. When copper sulphide is treated with hydrochloric acid, it gives off a gas _____________ which has a foul smell.
2. 2.

   Statements given below are incorrect. Write the correct statements.

   1. Lead nitrate crystals on strong heating decompose to form lead dioxide, nitrogen dioxide and oxygen gas.
   2. The reaction between magnesium and oxygen is an endothermic reaction.
   3. The decomposition of ammonium chloride into ammonia and oxygen is an exothermic reaction.
   4. Copper carbonate on strong heating leaves behind a residue which is green in colour.
   5. Ammonia gas and HCI gas react to form gaseous ammonium chloride.
3. 3.

   Match the statements in Column A, with those in Column B.

   Column A	Column B
   1. A chemical reaction which proceeds with the evolution of heat.	(a) Chemical change
   2. A chemical reaction which proceeds with the absorption of heat.	(b) Exothermic reaction
   3. Name of a change brought about by the decomposition of fruit juice.	(c) Oxygen
   4. Name of change brought about when current passes through an electric bulb.	(d) Endothermic reaction
   5. A gas given out when sodium nitrate crystals are heated strongly.	(e) Physical change

    

4. 4.

   State whether the following statements are true or false :

   1. Gold on hammering can form a thin sheet of gold.
   2. Burning of hydrogen and oxygen to form water is an example of physical change.
   3. Hydrogen gas react with chlorine gas to form liquid hydrochloric acid.
   4. Red lead oxide on strong heating gives off oxygen gas.
   5. Lead nitrate solution on mixing with potassium iodide solution forms green precipitate of lead iodide.
5. 5.

   Tick (√) the most appropriate answer.

   1. The reaction between magnesium and oxygen is :
      1. an endothermic reaction
      2. an exothermic reaction
      3. a catalysed reaction
      4. a reversible reaction
   2. The decomposition of sodium bicarbonate on heating is :
      1. an endothermic reaction
      2. a reversible reaction
      3. a catalysed reaction
      4. an exothermic reaction
   3. When lead nitrate crystals are strongly heated, the colour of one of the gas evolved is :
      1. greenish yellow
      2. pink
      3. reddish brown
      4. light grey
   4. When ammonia gas reacts with hydrochloric acid gas, the ammonium chloride is formed which is in :
      1. liquid state
      2. solid state
      3. gaseous state
      4. partly solid and partly gaseous state
   5. When silver nitrate solution is mixed with sodium chloride solution, a precipitate of silver chloride is formed, which is of :
      1. silvery colour
      2. yellow colour
      3. grey colour
      4. white colour
6. 6.

   What do you understand by the term 'Physical change'?