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Unit 2: Dissolving, solubility and chromatography

Solutions and solubility — HIA International - Grade 7 Revision Notes & Topical Questions

5 min read 9 parts Lesson 3 of 5 3 quizzes

📚 HIA International - Grade 7 Hub / Topical Revision
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Lesson summary

2.2 Solutions and solubility — HIA INTERNATIONAL notes: Describe concentration, saturation and solubility and how temperature affects them.Concentrated solution = a solution with a lot of solute particles in a volume of solvent.Dilute solution = a solution with fewer solute parti…

  • Judging concentration
  • Saturated solution
  • Proportion
  • Improving accuracy
  • Particle energy
  • Dissolving faster

Section 1 of 9Concentrated and dilute solutions

Concentrated solution
Concentrated solution a solution with a lot of solute particles in a volume of solvent.
Dilute solution
Dilute solution a solution with fewer solute particles.
Judging concentration
  • Judging concentration a darker coloured food dye solution is more concentrated.

Section 2 of 9Making different concentrations

1
Measure 10 cm3 of strong food dye solution into a test tube and call it solution A.
2
Make solutions B, C, D and E using 8, 6, 4 and 2 cm3 of dye solution.
3
Add water to each one to make a total of 10 cm3.
4
Place the tubes in order from A to E and compare their colour.
Accuracy
  • Accuracy measure the dye and water accurately, adding the last amount drop by drop with a pipette.
Result
  • A is the most concentrated and E the most dilute, because they differ in the number of dye particles.

Section 3 of 9Soluble, insoluble and saturated

Soluble
  • Soluble a solid that dissolves in a solvent such as water, for example sodium chloride and sugar.
Insoluble
  • Insoluble a solid that will not dissolve in water, for example iron filings.
Saturated solution
Saturated solution a solution in which no more solute will dissolve.
Solubility
  • Solubility some substances are more soluble than others, for example sodium chloride is far more soluble than lead chloride.

Section 4 of 9Comparing solubility

  • Method
    • measure how much of each solute dissolves in a known amount of solvent, usually 100 g of water at a stated temperature.
SaltSolubility in g per 100 g of water at 20 °C
Sodium chloride36
Copper sulfate32
Calcium chloride74
Lead chloride1
Sugar
  • 204 g dissolve in 100 g of water at 20 °C.
Proportion
  • Proportion twice the water dissolves twice the mass of solute.

Section 5 of 9Testing solubility in water

1
Place a measured volume of water in a separate test tube for each solute.
2
Add one spatula of the first solute and shake or stir.
3
Keep adding spatulas until no more dissolves.
4
Count the spatulas and repeat for the other solutes.
5
Record the results in a table.
  • Improving accuracy
    • measure the mass of solute added instead of counting spatulas.

Section 6 of 9Temperature and solubility

Temperature and solubility
Particle energy
  • Particle energy in hot water the particles have more energy, vibrate more and move more.
Dissolving faster
  • Dissolving faster most solutes dissolve more quickly and easily in hot water.
More dissolves
  • More dissolves the solubility of most solutes increases as the temperature increases.
Sugar
  • 204 g dissolve in 100 g of water at 20 °C and 362 g at 80 °C.
Graph
  • Graph solubility is plotted against temperature for salts such as potassium nitrate and copper sulfate, and all show a rising trend.

Section 7 of 9Other solvents

Water is not the only solvent.
Oil paint
  • Oil paint insoluble in water but dissolves in methanol, so brushes are cleaned with it.
    • (methylated spirit)
Nail polish
  • Nail polish insoluble in water but dissolves in nail polish remover, which contains propanone (acetone).

Section 8 of 9Key terms

TermMeaning
ConcentratedContaining a lot of solute in the solvent.
DiluteContaining little solute in the solvent.
SaturatedUnable to dissolve any more solute.
SolubilityHow much solute dissolves in a given amount of solvent.
SolubleAble to dissolve.
InsolubleUnable to dissolve.
SolventThe liquid that dissolves the solute.
SoluteThe substance that dissolves.

Section 9 of 9Exam technique

1
Saying saturated means concentrated at every temperature — saturated means no more will dissolve at that temperature.
2
Saying temperature does not affect solubility — it increases for most solids.
3
Saying insoluble means it cannot dissolve in any solvent — it may dissolve in another solvent.
4
Mixing up dilute and concentrated — concentrated has more solute particles.

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