Doc Brown's Chemistry Clinic

SELECTED SALT SOLUBILITY DATA and calculation examples

for KS3 Science and KS4 GCSE-IGCSE GCE-AS-A2-IB chemistry courses

return to Extra Aqueous Chemistry page

email comment?query

• Interpretation of graph eg

  • Reading graph: at 38^oC the solubility of copper sulphate, CuSO₄, is 28g of anhydrous salt per 100g of water.

  • Reading graph: at 84^oC the solubility of potassium sulphate, K₂SO₄, is 22g per 100g of water.

  • Ex Q1: How much potassium nitrate will dissolve in 20g of water at 34^oC?

    • At 34^oC the solubility is 52g per 100g of water,

    • so scaling down, 52 x 20 / 100 = 10.4g will dissolve in 20g of water

  • Ex Q2: At 25^oC 6.9g of copper sulphate dissolved in 30g of water, what is its solubility in g/100cm³ of water?

    • Scaling up, 6.9 x 100 /30 = 23g/100g of water (check on graph, just less than 23g/100g water).

  • Ex Q3: 200 cm³ of saturated copper solution was prepared at a temperature of 90^oC. What mass of copper sulphate crystals form if the solution was cooled to 20^oC?

    • Solubility of copper sulphate at 90^oC is 67g/100g water, and 21g/100g water at 20^oC.

    • Therefore for mass of crystals formed = 67 - 21 = 46g (for 100 cm³ of solution).

    • However, 200 cm³ of solution was prepared,

    • so total mass of copper sulphate crystallised = 2 x 46 = 92g

• Note: The density of water is close to 1.0g/cm³ or ml, so for approximate purposes. the volume in cm³ or ml of just the water is numerically close to the value in g, i.e. 100 cm³ of water or solution is about 100g of water.

Examples of

SALT SOLUBILITY DATA

SOLUBILITY

g salt / 100g water

Salt name

potassium nitrate

potassium sulphate

sodium chloride

hydrated copper(II) sulphate

and formula

Temp. ^oC

KNO₃

K₂SO₄

NaCl

CuSO₄ (anhydrous *)

0

13.9

7.4

35.7

14.3

10

21.2

9.3

35.8

17.4

20

31.6

11.1

36.0

20.7

30

45.3

13.0

36.2

24.2

40

61.4

14.8

36.5

28.7

50

83.5

16.5

36.8

33.8

60

106.0

18.2

37.3

40.0

70

19.8

37.6

47.0

80

21.4

38.1

56.0

90

22.9

38.6

67.5

100

24.1

39.2

80.0

* multiply by 1.562 for hydrated crystals CuSO₄.5H₂O

Copyright Dr W P Brown 2000-2009 All rights reserved including revision notes pages, quizzes, puzzles, worksheets

Important concepts to understand, facts to know, information points to learn and revise when studying for exams, lesson preparation, teaching and learning to study for yourself or students pupils parents parental info help with revising topics homework coursework projects and assignments in understanding science chemistry courses