The solubility of highly soluble, thermally unstable salts such as ammonium chloride may be determined by back titration.
In one experiment a 5.00 mL saturated solution of ammonium chloride, NH₄Cl, at 20.0 °C, was diluted with distilled water to 250.0 mL in a standard fl\ask.
A 20.0 mL aliquot of this solution was added to 10.0 mL of 0.400 M NaOH solution. The solution was heated to drive off the ammonia formed by this reaction.
When the flask had cooled, the excess hydroxide ions were neutralised by 14.7 mL of 0.125 M HCl solution. The molar mass of ammonium chloride is 53.5 g mol^–1.

a) i. Write an equation for the neutralisation reaction.

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ii. Determine the amount, in mole, of NaOH that was originally added to the ammonium chloride solution.

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iii. Determine the amount, in mole, of ammonium chloride in the 20.0 mL aliquot.

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iv. Calculate the amount, in mole, of ammonium chloride in 5.00 mL of the saturated solution.

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v. Calculate the solubility, in gL^–1 of ammonium chloride in water at 20 °C.

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b) If the burette was rinsed with water instead of acid before the titration, how would the calculated solubility of
ammonium chloride be affected? Explain your answer.

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