IGCSEChemistryEdexcelRevision Notes1. Principles of ChemistryStates of MatterSolubility

Solubility (Edexcel IGCSE Chemistry)

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Edexcel ChemistryEdexcel Chemistry (Modular): Unit 1

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Solubility

  • Solubility is a measurement of how much of a substance will dissolve in a given volume of a liquid
    • The liquid is called the solvent
    • The solubility of a gas depends on pressure and temperature

  • Different substances have different solubilities
  • Solubility can be expressed in g per 100 g of solvent
  • Solubility of solids is affected by temperature
    • As temperature increases, solids usually become more soluble

  • Solubility of gases is affected by temperature and pressure; in general:
    • As pressure increases, gases become more soluble
    • As temperature increases, gases become less soluble

Solubility curves

  • Solubility graphs or curves represent solubility in g per 100 g of water plotted against temperature
  • To plot a solubility curve, the maximum mass of solute that can be dissolved in 100 g of water before a saturated solution is formed, is determined at a series of different temperatures

Solubility curve for three salts

A graph to show the solubility curves of three different salts

While the solubility of most salts increases with temperature, sodium chloride, or common salt, hardly changes at all

Worked example

Use the solubility curve to answer these questions:

  1. Determine how much potassium nitrate will dissolve in 20 g of water at 50 °C?
  2. 200 cm3 of saturated lead(II) nitrate solution was prepared at a temperature of 90 °C. What mass of lead(II) nitrate crystals form if the solution was cooled to 40 °C?

Answers:

  1. At 50 °C, the solubility of potassium nitrate is 68 g per 100 g of water
    So scaling, 68 x (20 / 100) = 13.6 g of potassium nitrate will dissolve in 20 g of water
  2. Solubility of lead(II) nitrate at 90 oC is 118 g / 100 g water, and 64 g / 100 g water at 40 °C.
    Therefore for mass of crystals formed = 118 – 64 = 54 g (for 100 cm3 of solution).
    However, 200 cm3 of solution was prepared,
    So total mass of lead(II) nitrate crystallised = 2 x 54 = 108 g

Examiner Tip

As temperature increases, solids usually become more soluble and gases become less soluble.

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    Stewart

    Author: Stewart

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    Stewart has been an enthusiastic GCSE, IGCSE, A Level and IB teacher for more than 30 years in the UK as well as overseas, and has also been an examiner for IB and A Level. As a long-standing Head of Science, Stewart brings a wealth of experience to creating Exam Questions and revision materials for Save My Exams. Stewart specialises in Chemistry, but has also taught Physics and Environmental Systems and Societies.