(a) State an indicator suitable for the titration of; (i) dilute HCl and NaOH\(_{3(aq)}\) (ii) dilute CH\(_3\)COOH and KOH\(_{(aq)}\) (iii) dilute HCl and N...
Question 1 Report
(a) State an indicator suitable for the titration of;
(i) dilute HCl and NaOH\(_{3(aq)}\)
(ii) dilute CH\(_3\)COOH and KOH\(_{(aq)}\)
(iii) dilute HCl and NH\(_{3(aq)}\).
Give a reason for your answer in each case.
(b) Calculate the volume of water that would be added to 50 cm\(^3\) of 0.10 mol dm\(^{-3}\) of HCI to dilute it to 0.010 mol dm \(^{-3}\)
(c) Name one gas that could be used to demonstrate the fountain experiment.
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).
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