water and solutions. a solvent is a substance that dissolves other materials to form a solution e.g....
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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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