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Solutions


 

How is a solution made?

When a substance dissolves in a liquid a solution is made.

E.g. –

  • Seawater is a solution of salt and other substances in water.
  • Fizzy drinks contain the gas carbon dioxide dissolved in water.
  • Fish breathe oxygen that is dissolved in the water around them.
  • Liquids will dissolve in liquids E.g. – Oil dissolves in petrol
  • Solids will dissolve in solids E.g. – Brass is made by dissolving copper metal in molten zinc metal

 

Some substances soluble in water

 

  • Soap
  • Sugar
  • Salt
  • Milk powder
  • Washing- up liquid
  • Coffee granules
  • Soy sauce
  • Bath salt
  • Soluble asprin

 

What is meant by ‘soluble’?

Substances that dissolve are called ‘soluble’.

 

What is meant by ‘insoluble’?

Substances that do not dissolve are called ‘insoluble’.

 

What is a ‘solvent’?

The liquid in which a substance dissolves to form a solution is called a solvent.

E.g. – The best solvent in the world is water.

 

What is a ‘solute’?

The substance that dissolves is called the ‘solute’.

 

What is a ‘solution’?

When a solute dissolves in a solvent, that mixture is called a ‘solution’.

making-salt-solution

 

 

E.g. –

  • If you put a teaspoon of salt in a glass of water, the salt seems to disappear and you have a salt solution.
  • If you put a teaspoon of sugar in a glass of water, the sugar seems to disappear and you have a sugar solution.

 

 

Particles

 

Making a sugar Solution

 

If you add a teaspoon of sugar to a glass of water, all the sugar will dissolve. How does this happen?

 

Water is made of very tiny particles. Sugar is made of slightly larger particles. Water particles have small spaces between them. They are close together and always moving. So if you add a teaspoon of sugar to a glass of water, the small moving water particles get between the larger sugar particles. Therefore we can see, sugar dissolves in water. Now you have a sugar solution.

 

Making a saturated sugar solution

 

If you add more and more sugar to a glass of water, eventually no more sugar will dissolve. How does this happen?

 

If you add more and more sugar to a glass of water, gradually the amount of water particles will decrease and the amount of sugar particles will increase. Eventually there will be no more water particles to get between the sugar particles. Now you have a saturated sugar solution.

 

What is a ‘saturated solution’?

A solution that contains all the dissolved substances it can hold is called a saturated solution. Some substances are very soluble. That means a lot of them dissolve in a certain amount of liquid. Some substances are slightly soluble.

 

 

Evaporating

 

What is meant by ‘evaporating’?

The changing of a liquid into a vapour is called evaporating.

 

Getting the dissolved sugar in the sugar solution back again

 

Heat the sugar solution on a saucer. Then the water in the sugar solution can evaporate away leaving the sugar on the saucer.