A student carries out an investigation into how the solubility of solid potassium nitrate changes with temperature.
The student:
step 1 places 100 cm$^3$ of water in a beaker at room temperature
step 2 finds the mass of the beaker containing the water
step 3 puts some potassium nitrate into the water
step 4 stirs the mixture until every part of the potassium nitrate has dissolved
step 5 repeats steps 3 and 4 until a small amount of solid is still undissolved in the beaker
step 6 finds the mass of the beaker containing the water and potassium nitrate
step 7 repeats steps 1 to 6 with water at different temperatures
step 8 works out the mass of potassium nitrate dissolved in the water at each temperature.
(a(i))[1]
The student has left out a key measurement.
State the measurement that must be taken.
(a(ii))[1]
The student’s data are presented in Table 1.1.
Estimate the mass of potassium nitrate dissolved in 100 cm$^3$ of water at $55^\circ$C.
(a(iii))[2]
The student sees a solid in the beaker after the solution made at $75^\circ$C is left at room temperature.
Explain why.
(b)[1]
Suggest why the student does not carry out the experiment at $115^\circ$C.
(c)[1]
Explain why the method the student uses gives a value for solubility that is greater than the true value.