A student finds the solubility of solid ammonium chloride in water at 60^{\circ}C.
The student:
step 1 places $100\text{ cm}^3$ of water in a beaker
step 2 warms the water
step 3 determines the mass of a weighing bottle that contains ammonium chloride
step 4 puts some of this ammonium chloride into the water
step 5 mixes the contents to make the solid dissolve
step 6 repeats steps 4 and 5 until a small quantity of solid is still undissolved in the beaker
step 7 measures the mass of the weighing bottle and the ammonium chloride left over
step 8 works out the mass of ammonium chloride added to the water.
(a(i))[1]
State one further measurement the student needs to take in order to calculate the solubility.
(a(ii))[2]
Use the data to work out the solubility of ammonium chloride at $60\,^{\circ}\text{C}$ in $\text{g dm}^{-3}$.
(a(iii))[1]
Explain why the method the student uses gives a higher value for the solubility than the true value.
(b)[1]
Estimate the solubility of ammonium chloride at a temperature of $20\,^{\circ}\text{C}$.
(c)[1]
Suggest why the technique used for ammonium chloride cannot be used to determine the solubility of ammonia.