Edexcel IGCSE Chemistry 1.6C solubility curves

Practise solubility-curve questions by plotting data, drawing smooth curves and reading masses or temperatures from graphs.

Exam points

Plot solubility data accurately and draw labelled smooth curves for each salt.
Read temperatures or masses from a solubility curve, extending the curve when needed.
Calculate mass crystallised by subtracting solubility readings at two temperatures.

[Maximum number: 5]

A student investigates the solubility of potassium nitrate in water.
She measures the masses of potassium nitrate that dissolve in 25 cm3 of water at different temperatures.

The table shows the student's results. One of the results is anomalous.

Table for Question 1.6C Solubility curves question 1 — Edexcel IGCSE Chemistry

(a)

Plot the results on the grid.

[ 1 ]

(b)

Draw a circle around the anomalous result.

[ 1 ]

point at $50^{\circ} \mathrm{C}$ and 17.5 g circled on grid/in table

ALLOW ECF from
incorrect plotting

(c)

Ignoring the anomalous result, draw a curve of best fit.

Figure for Question (c) — Edexcel IGCSE Chemistry

[ 1 ]

(d)

Use your graph to find the maximum mass of potassium nitrate that dissolves in $25 \mathrm{~cm}^{3}$ of water at $75^{\circ} \mathrm{C}$ .

Show on your graph how you obtained your answer.
mass = g

[ 2 ]

M1 curve extended to $75^{\circ} \mathrm{C}$

M2 correct mass read from graph to the nearest grid line

expected answer around 39 to 40 g

0 marks if curve not extended

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1.6C Solubility curves question 1

Question (a)

Question (b)

Question (c)

Question (d)