Water Purification 2

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Potable Water in Saudi Arabia

There are many methods for producing potable water. In Saudi Arabia, the conditions are very different to the UK and so a different method is used.

Seawater

Rainfall levels are low, and so fresh water supplies can't be relied upon.
Seawater is used as an alternative to fresh water.

Treating seawater

Seawater must be desalinated (have the salt removed) to make it potable. There are 2 desalination methods:
1. Distillation: boiling seawater creates steam, which then condenses to give pure water.
2. Reverse osmosis: seawater is passed through a selective membrane that only allows water molecules through.

Cost of treating seawater

The major disadvantage of both desalination methods is that they need a high amount of energy, making them expensive.

Mixtures are made of 2 or more substances (elements or compounds) that haven't been chemically combined. Mixtures can be separated. Their chemical properties don't change because they have been mixed with another substance. Mixtures are common in everyday life:

Air

Air is a mixture of gases, including oxygen, nitrogen and carbon dioxide.

Pasta and vegetables

A bowl with both pasta and vegetables in is a mixture.
This is because there have been no chemical reactions between the vegetables and the pasta.

Distillation

Distillation is a special technique used to separate mixtures of liquids. It uses the different boiling points of liquids to separate them. There are 2 types of distillation:

Simple distillation

Separates 2 liquids with different boiling points.
- The mixture is heated until the liquid with the lower boiling point starts to boil.
- The vapour released passes through a condenser, where the gas cools back into a liquid.

Fractional distillation

Separates lots of liquids with different boiling points.
- The mixture is slowly heated until the liquid with the lowest boiling point boils and then condenses.
- Then we increase temperature slowly to collect (boil then condense) the other fractions.