TEST OF PRACTICAL KNOWLEDGE QUESTION (a) State an indicator suitable for the titration of; (i) dilute HCl and NaOH\(_{3(aq)}\) (ii) dilute CH\(_3\)COOH and ...

Answer Details

(a) Suitable indicators for the titrations

• (i) Dilute HCl (strong acid) and NaOH (strong base): either methyl orange or phenolphthalein is suitable. Reason: the salt formed (NaCl) is neutral and there is a large, sharp pH change at the end point that spans the ranges of both indicators.
• (ii) Dilute CH₃COOH (weak acid) and KOH (strong base): use phenolphthalein. Reason: the salt formed is of a weak acid and a strong base, so it hydrolyses to give an alkaline solution (pH > 7) at the end point, within the colour-change range of phenolphthalein.
• (iii) Dilute HCl (strong acid) and NH₃ (weak base): use methyl orange. Reason: the salt formed is of a strong acid and a weak base, so it hydrolyses to give an acidic solution (pH < 7) at the end point, within the range of methyl orange.

(b) Volume of water to add for dilution

Using \(C_1V_1 = C_2V_2\):

\[0.10 \times 50 = 0.010 \times V_2\]

\[V_2 = \frac{0.10 \times 50}{0.010} = 500\text{ cm}^3\]

Volume of water added \(= 500 - 50 = 450\text{ cm}^3\).

(c) Gas for the fountain experiment

Ammonia (NH₃), because it is extremely soluble in water (hydrogen chloride gas may also be used).