Chapter 3: Let us answer these (page 47)

Q1. Dissolve a small amount of NaHCO₃ in water. Add 1 drop of methyl orange into it. What is the colour of the mixture?

Ans:- Yellow as the solution is basic.

Q2. Add lime juice in the above solution till the evolution of the gas stops. What is the colour of the mixture now?

Ans:- Pink as the solution becomes acidic.

Q3. How many grams of sulphuric acids(H₂SO₄) will be needed to react completely with a solution containing 10.6 g of sodium carbonate (Na₂CO₃)?
Ans:- Sodium carbonate reacts with sulphuric acid to form sodium sulphate,water and carbondioxide.

   Na₂CO₃ (106kg) + H₂SO₄ (98kg)  -------> Na₂SO₄ (142kg) + H₂O (18kg) + CO₂(44kg)

     For the complete reaction, 98kg of H2SO4 is required to neutralize 106 of Na2CO3

           Hence, the amount of sulpheric acid needed =98X10.6/106 g = 9.8g

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