Solubility

Experiment 9 To investigate how the solubility of potassium nitrate crystals varies with temperature

In this exercise, solutions of different concentrations of potassium nitrate are heated and allowed to crystallise on cooling. The temperature at which crystals begin to form is plotted against the concentration of the salt in g per 100 cm? to give the solubility curve of the

CXC criteria tested
(a) Manipulation – proper use of apparatus
(b) Attitudes – safety
(c) Organisation – presentation of lab report
(d) Interpretation – making logical deductions

Apparatus and materials
boiling tube containing 15.0 g of potassium nitrate
50 cm burette
250 cm beaker to act as a water bath thermometer, – 10 to + 110°C (× 0.5°C)

Procedure
(a) Using the burette, add 10.0 cm’ of distilled water to the potassium nitrate in the
bOIling tube.
(b) Clamp the boiling tube and its contents vertically in a water bath and warm carefully, while stirring, until all the solid dissolves.
(c) Place the thermometer into the boiling tube and after a few minutes remove the boiling tube from the water bath. Allow the boiling tube and its contents to cool, stirring gently with the thermometer. Record the temperature at which crystals first appear.
(d) Add to the contents of the boiling tube a further 2.0 cm’ of distilled water and repeat
the above procedure, noting the temperature at which the crystals first appear.
(e) Repeat the procedure, adding further 2.0 cm portions of water to obtain a total of

Treatment of results
(a) In each determination, 15.0 g of potassium nitrate were used while the volume of water varied from 10.0 cm° to 12.0 cm° to 14.0 cm°
etc. For each determination. find the
solubility of the potassium nitrate in g per 100 cm of water and tabulate your results.

(b) Plot a graph of solubility of potassium nitrate in g per 100 cm water against temperature in °C.

(c) What deductions can you draw from your graph?

Exercises

1. Use your graph to find the solubility of potassium nitrate in g per 100 cm water at (a)
50°C, (b) 60°C.

2. Potassium iodide dissolves endothermically in water. What effect will increasing tempera.
ture have on the solubility of potassium iodide in water?
Explain your answer.Experiment 9 To investigate how the solubility of potassium nitrate crystals varies with temperature

In this exercise, solutions of different concentrations of potassium nitrate are heated and allowed to crystallise on cooling. The temperature at which crystals begin to form is plotted against the concentration of the salt in g per 100 cm? to give the solubility curve of the

CXC criteria tested
(a) Manipulation – proper use of apparatus
(b) Attitudes – safety
(c) Organisation – presentation of lab report
(d) Interpretation – making logical deductions

Apparatus and materials
boiling tube containing 15.0 g of potassium nitrate
50 cm burette
250 cm beaker to act as a water bath thermometer, – 10 to + 110°C (× 0.5°C)

Procedure
(a) Using the burette, add 10.0 cm’ of distilled water to the potassium nitrate in the
bOIling tube.
(b) Clamp the boiling tube and its contents vertically in a water bath and warm carefully, while stirring, until all the solid dissolves.
(c) Place the thermometer into the boiling tube and after a few minutes remove the boiling tube from the water bath. Allow the boiling tube and its contents to cool, stirring gently with the thermometer. Record the temperature at which crystals first appear.
(d) Add to the contents of the boiling tube a further 2.0 cm’ of distilled water and repeat
the above procedure, noting the temperature at which the crystals first appear.
(e) Repeat the procedure, adding further 2.0 cm portions of water to obtain a total of

Treatment of results
(a) In each determination, 15.0 g of potassium nitrate were used while the volume of water varied from 10.0 cm° to 12.0 cm° to 14.0 cm°
etc. For each determination. find the
solubility of the potassium nitrate in g per 100 cm of water and tabulate your results.

(b) Plot a graph of solubility of potassium nitrate in g per 100 cm water against temperature in °C.

(c) What deductions can you draw from your graph?

Exercises

1. Use your graph to find the solubility of potassium nitrate in g per 100 cm water at (a)
50°C, (b) 60°C.

2. Potassium iodide dissolves endothermically in water. What effect will increasing tempera.
ture have on the solubility of potassium iodide in water?
Explain your answer.Experiment 9 To investigate how the solubility of potassium nitrate crystals varies with temperature

In this exercise, solutions of different concentrations of potassium nitrate are heated and allowed to crystallise on cooling. The temperature at which crystals begin to form is plotted against the concentration of the salt in g per 100 cm? to give the solubility curve of the

CXC criteria tested
(a) Manipulation – proper use of apparatus
(b) Attitudes – safety
(c) Organisation – presentation of lab report
(d) Interpretation – making logical deductions

Apparatus and materials
boiling tube containing 15.0 g of potassium nitrate
50 cm burette
250 cm beaker to act as a water bath thermometer, – 10 to + 110°C (× 0.5°C)

Procedure
(a) Using the burette, add 10.0 cm’ of distilled water to the potassium nitrate in the
bOIling tube.
(b) Clamp the boiling tube and its contents vertically in a water bath and warm carefully, while stirring, until all the solid dissolves.
(c) Place the thermometer into the boiling tube and after a few minutes remove the boiling tube from the water bath. Allow the boiling tube and its contents to cool, stirring gently with the thermometer. Record the temperature at which crystals first appear.
(d) Add to the contents of the boiling tube a further 2.0 cm’ of distilled water and repeat
the above procedure, noting the temperature at which the crystals first appear.
(e) Repeat the procedure, adding further 2.0 cm portions of water to obtain a total of

Treatment of results
(a) In each determination, 15.0 g of potassium nitrate were used while the volume of water varied from 10.0 cm° to 12.0 cm° to 14.0 cm°
etc. For each determination. find the
solubility of the potassium nitrate in g per 100 cm of water and tabulate your results.

(b) Plot a graph of solubility of potassium nitrate in g per 100 cm water against temperature in °C.

(c) What deductions can you draw from your graph?

Exercises

1. Use your graph to find the solubility of potassium nitrate in g per 100 cm water at (a)
50°C, (b) 60°C.

2. Potassium iodide dissolves endothermically in water. What effect will increasing tempera.
ture have on the solubility of potassium iodide in water?
Explain your answer.

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