Available Answers

1. 1.

   Give a balanced equation for each of the characteristics accompanying a chemical reaction.

   1. Change in colour - thermal decomposition of
      1. Mercury [II] oxide
      2. Copper [II] carbonate
   2. Evolution of a gas - addition of active metal
      1. Zinc to dilute hydrochloric acid
      2. Iron to dilute sulphuric acid
   3. Evolution of heat - addition of
      1. A basic oxide to water
   4. Formation of a precipitate - addition of
      1. Silver nitrate solution to dilute hydrochloric acid
      2. Copper [II] sulphate solution to sodium hydroxide solution.
2. 2.

   Given below are representations of different chemical reactions. State the type of each diagrammatic representation represents. Select from -

   Decomposition reaction, Simple displacement reaction, Double decomposition, Direct combination reaction

   

3. 3.

   Match the reactions given in Column-I with their type in Column-II.

   Column I - Reaction	Column II - Type of reaction
   a. 2Ca + O2 → 2CaO	A: Displacement
   b. Ca + 2H2O → Ca(OH)2 + H2	B: Double decomposition
   c. CaSO4 + 2NH4OH → (NH4)2SO4 + Ca(OH)2	C: Direct combination
   d. Ca(OH)2  --Δ→ CaO + H2O	D: Decomposition

    

4. 4.

   Give a reason why the reaction 'C + O2  → CO2' - is called a 'synthesis reaction'.

5. 5.

   Give an example each of a direct combination reaction between [give balanced equations].

   1. Two elements - one of them is an active metal.
   2. An element and a compound - both neutral gases.
   3. Two compounds - one of them is a basic oxide.
6. 6.

   Give balanced equations for the following direct combination reactions involving conversion of -
   In one step only-

   1. A metal above calcium in the activity series of metals - to a basic oxide.
   2. A yellow non-metal to an acidic oxide.
   3. Two neutral gases - to an acidic gas.
   4. A basic gas - to an ammonium salt [ammonium chloride]/
   5. A basic oxide - to an alkali [calcium hydroxide].
   6. A trivalent metal - to its metallic chloride.

   In two steps -

   1. Carbon to Carbonic acid.
   2. Sulphur to Sulphurous acid.
   3. Phosphorus to Phosphoric acid.