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What is dissolving?

• Learning Objectives : • Explain dissolving using the

Particle model• Explain why mass is

conserved. • Evaluate a scientific

experiment and make improvements.

Key Words:•Dissolve •Soluble•Insoluble•Saturated •Conservation of mass

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Starter – Match the keywords to their description

A- solution

B- solvent

C- solute

D- solubility

E- soluble

F- insoluble

1- A solid that has dissolved.

2- A solid dissolved in a liquid.

3-The amount of a solid that will dissolve in 100g of a liquid.

4-Describes a solid that cannot dissolve in a liquid

5-Describes a solid that can dissolve in a liquid

6- The liquid a solid has dissolved in.

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Does everything dissolve?

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Calcium carbonate is not soluble in water because the calcium carbonate and water particles are not able to mix.

Copper sulfate is soluble in water because the copper sulfate and water particles are able to interact and mix together.

calcium carbonate copper sulfate

water

water

What happens when something dissolves?

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Dissolving in action?

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+

50 g 10 g+

Conservation of mass

If 10 g of salt is added to 50 g of pure water, what is the mass of the solution?

When the salt has dissolved, you can’t see it any more. How could you check that the salt is still there?

?60 g

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How much salt?

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Conservation of mass – extension

If 10 g of salt is added to 50 g of seawater, what is the mass of the solution?

How much salt will be recovered if the mixture is separated by evaporation?

+

50 g 10 g+ ?60 g

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Does a solid keep dissolving?

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Supersaturated solutions

Supersaturated solutions are very saturated indeed.

The solute will stay in solution until a ‘seed’ crystal is added, and then it will crystallise out of the solution very quickly.

When it does this, it gives out heat energy. Supersaturated solutions are therefore used in heat packs.

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Practical – Making a saturated solution

1. Put 50ml of water in a 100ml beaker2. Record the temperature of the water.3. Add salt to the water, 1 spatula at a time and stir until dissolved. 4. How much salt dissolves before the solution becomes saturated?

In your books• Write a method.• Draw a labelled diagram.• Show your results.• Write a conclusion.• Write at least 5 things you could change to make this experiment

more of a fair test.

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Solubility of gases

Gases are unusual because their solubility decreases when the solvent gets hotter.

Fish and other organisms that live in water survive by taking in oxygen that has dissolved in the water.

Some scientists think that global warming is causing sea temperatures to rise.

What effect do you think rising sea levels will have on the creatures that live in the sea?