Question

Read the following question and answer as per the direction given below :

(a) Statement I is true; Statement II is true; Statement II is a correct explanation of Statement I.

(b) Statement I is true; Statement II is true; Statement II is not the correct explanation of Statement I.

(c) Statement I is true; Statement II is false. 

(d) Statement I is false; Statement II is true.

Statement I : In the titration of Na₂CO₃ with HCI using methyl orange indicator, the volume required at the equivalence point is twice that of the acid required using phenolphthalein indicator.

Statement II : Two moles of HCI are required for the complete neutralisation of one mole of Na₂CO₃

Answer 1

Correct option  (b) Statement I is true; Statement II is true; Statement II is not the correct explanation of Statement I.

Explanation:

Neutralisation of Na₂CO₃ with acid (HCl) takes place in two steps

Thus, for half neutralisation of Na₂CO₃, phenolphthalein (HPh) can be used as an indicator. By use of HPh, half of the titre value of Na₂CO₃ is obtained.

The use of methyl orange as indicator in this step gives the another half of the titre value of Na₂CO₃.

However, the full titre value of Na₂CO₃ can be obtained by using methyl orange as indicator.