WATER AND SOLUTIONS

• A solvent is a substance that dissolves other materials to form a solution e.g. Water, White Spirit, nail Varnish remover.

A substance that dissolves in the solvent is called the solute e.g. coffee, salt, sugar.

A solution is a mixture of a solute and a solvent.

Examples of Solutions• Sugar (solute) in water (solvent)• Copper sulfate (solute) in water (solvent)• Sea water

SOLUTION

solute + solvent >>>> solution

Mass of solute + solvent = Mass of solution

Glass ofDilute orange solution

Bottle ofConcentrated

orange solution

SOLUTIONS• A dilute solution has a small amount of solute in

a large amount of solvent.• A concentrated solution has a large amount of

solute in a small amount of solvent.

Dilute solution

of copper sulfate

Concentrated solution

of copper sulfate

Dilute & Concentrated Solutions

• A dilute solution has a small amount of solute in a large amount of solvent.

• A concentrated solution has a large amount of solute in a small amount of solvent.

A Solution can be made concentrated by adding more solute.Eventually the solvent will not dissolve any more solute at that temperature. Some solute will remain un-dissolved at the bottom of the beaker

A Solution can also be made concentrated by removing some solvent - evaporation

• Saturated Solution: A solution that contains as much dissolved solute as possible at a given temperature

• The solubility of a solvent increases with temperature.

Saturated Solution

Solubility

• The solubility of a substance is its mass (in grams) that will dissolve in 100 grams of solvent at a fixed temperature e.g.

• Solubility of copper sulfate is 40g at 60°C.

Solubility varies from solute to solute

Solubility and Temperature

• The amount of solute that will dissolve in a solvent depends on the temperature e.g.

• Coffee grains dissolve more easily in hot water than in cold water.

In a concentrated solution some solute will remain un-dissolved at the bottom of the beaker. This solute can be made to dissolve by increasing the temperature of the solvent

Solubility Curve for copper sulphate (solute) in water (solvent) –

The curve of the graph shows that as the temperature of the solvent increases more solute will dissolve – click to show

Method;• Grind up copper sulphate using a pestle and mortar to help it dissolve more quickly• Gradually add the powdered substance to 100 cm’ of water in a beaker stirring to help the powder to dissolve. Continue adding until the solute no longer dissolves but settles at the bottom of the beaker – solution is concentrated @ room temperature •Heat the water to about 60 °C and note that excess copper sulphate dissolves (as seen slide).• Add more copper sulphate until no more will dissolve – solution is concentrated @ 600C•Pour about half of the solution into a warm evaporating basin and put it aside to cool slowly. •Cool the other half quickly by holding the beaker under running water from the tap.

Result - Crystals of Copper Sulphate are formedConclusion – Crystals are formed when a hot concentrated solution is cooled

Experiment – To grow crystals of Copper Sulphate

Crystallisation: The forming of crystals when a hot saturated solution is cooled. When a hot saturated solution of copper sulphate is allowed to cool, blue crystals of copper sulphate are formed.

Crystallisation

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