Solutions and Formation of Crystals

Solvent

Water and sugar: Water dissolves sugar, so it is a solvent.

Water and plastic: Water does not dissolve plastic, so it is not a solvent in this case.

Other Solvents:

1. Hydrochloric Acid (HCl): Dissolves food in the stomach.
2. Ethanol: Dissolves ink.

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Solute

• Sugar in Water: Sugar is the solute when it dissolves in water.
• Food in HCl and Blood Plasma: Food particles are solutes in both hydrochloric acid and blood plasma.
• Insoluble Substances: If a substance does not dissolve in a solvent, it is insoluble. For example, plastic is insoluble in water.
• Gaseous Solutes: A solute can also be a gas. For example, oxygen dissolved in water is essential for fish.

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Solution

Sand and Water: Sand and water is not a solution because sand does not dissolve (is insoluble) in water.

Salt and Water: Salt and water is a solution as salt dissolves (is soluble) in water.

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Concentrated and Dilute Solutions

• Dilute Solution: Contains a small amount of solute in a large amount of solvent.
• Concentrated Solution: Contains a large amount of solute in a small amount of solvent.
• Colour Intensity: A more intense colour indicates a higher concentration.

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Solubility

Temperature: Solubility increases with temperature.

Drawing Solubility Graphs: Do not use a ruler to connect the dots; draw freehand.

Increasing Solubility

1. Increase the temperature.
2. Stir the solution to help the solute dissolve faster.
3. Add more solvent.

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Crystallisation

Crystal Formation Process

1. Dissolve solute: Dissolve solute in water until no more can dissolve at that temperature.
2. Increase temperature: Dissolve more solute to make the solution saturated.
3. Cool down: Turn off the heat and place the solution in a fridge for 24 hours.
4. Result: Crystals form at the bottom of the container.

Cooling and Crystal Size

• Cooled quickly by ice: Small crystals.
• Cooled slowly: Large crystals.

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Mandatory Experiment