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Pure Substances�and Mixtures

Grade 7 Science

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Concentration�and Solubility

Lesson 4

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Solubility

  • When substances dissolve in a solvent, the particles of the solute mix between the particles of the solvent – this is called diffusion.
  • The mass of the solution changes but the volume of the solution stays the same.

BEFORE DIFFUSION

AFTER DIFFUSION

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Solubility

  • Some particles are polar (have charges) and some are non-polar (have no charges).

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    • Examples of polar molecules:
      • water, sugar, salt

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    • Examples of non-polar molecules
      • oil, gasoline

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Solubility

  • When deciding if substances will dissolve together, we follow the rule like dissolves like
    • This means that polar solvents will only dissolve polar solutes and non-polar solvents will only dissolve non-polar solvents
      • e.g. Sugar is polar so it will dissolve in the polar solvent water but will not dissolve in the non-polar solvent oil

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Soluble and Insoluble

If a solute is able to dissolve in a solvent, we say it is soluble.

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If a solute is unable to dissolve in a solvent, we say it is insoluble.

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Concentration

  • The concentration of a solution tells us the quantity of solute that is dissolved in a certain volume of solution.

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    • A concentrated solution has a large number of solute particles for a given volume of solution.

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    • A dilute solution has a small number of solute particles for a given volume of solution.

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Example

      • e.g. one solution contains 10 g of sugar dissolved in 100 mL of water and the other contains 50 g of sugar dissolved in 100 mL of water – the first solution (less sugar) is more dilute and the second (more sugar) is more concentrated

10g of sugar

100mL of water

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MORE DILUTE

50g of sugar

100mL of water

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MORE CONCENTRATED

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Calculating Concentration

  • We can calculate concentration:

 

 

Concentration

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Try it!

  • Calculate the concentration if 6.0 g of salt are dissolved in 200 mL of water.

 

 

 

Don’t forget your units!

The concentration of the solution is 0.03g/mL.

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Saturated vs. Unsaturated Solutions

A solution in which no more solute can be dissolved is called saturated.

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A solution in which more solute can be dissolved is called unsaturated.

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Solubility

  • The solubility of a substance is a measure of how much of the substance can dissolve in a certain solvent at a certain temperature.

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  • For example, in water that is 20°C:
    • The solubility of sugar is 206g/100mL
    • The solubility of salt is 36g/100mL

 

 

Solubility

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Try it!

  • 9.3 g of baking soda will dissolve in 100 mL of water. What is its solubility?

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The solubility of baking soda is 0.093g/100mL.

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Important Formulas

 

Concentration

 

Solubility