Chemistry Grade 8 Revision and Practice

 






Emulsions:

An emulsion is a finely dispersed mixture of two or more liquids that do not dissolve in each other.

Emulsifiers:

Salad cream also contains oil and water. Salad cream has egg yolk added. This keeps the oil droplets mixed with the water. It stops the oil and water separating out into layers.

A substance that does this is called an emulsifier.

Detergents:

Many detergents are made from the products of crude oil. Washing-up liquid is an example.

Detergents are substances which help the cleaning action of water.

Water is good at dissolving many things. However, it cannot dissolve oil or grease. This is where detergents help. They act as emulsifiers. They remove grease and keep it dispersed in water.

Soaps:

We can summaries the reaction as:

Oil/fat  +  sodium hydroxide  à  soap  +  glycerol

Making soap is called saponification.

Preservatives and anti-oxidants:

Fresh foods soon ‘go off’ as they are attacked by bacteria or oxygen in the air. For example, fats in food are oxidized to acids, making it rancid.

However, preservatives and anti-oxidants protect the food


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