Chemistry GCSE


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The Alkali Metals

They are called alkali metals because their hydroxides dissolve in water to give an alkaline solution.

They are soft, silvery-white in colour and have a low density. They also have much lower melting and boiling points your average metal; this is because its metallic bonds are a lot weaker.

Alkali metals react with water to produce hydrogen gas. You also get a hydroxie solution (OH- ions).

Sodium carbonate is used to make glass and soda crystals.

Sodium Hydroxide is a strong Alkali with many industrial uses like oven cleaner and bleach.

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Sulphuric Acid

Sulphuric acid is produced industrially using the contact process.

The Contact process

1. S + 0(2) --> SO(2)

2. 2SO(2) + O(2) <--> 2SO(3)      (using vernadium pentoxide -V(2)H(5)

3. SO(3) + H(2)SO(4) --> H(2)S(2)O(7)

4.H(2)S(2)O(7) + H(2)O --> 2H(2)SO(4)

450 degrees C, 1-2 atmospheres.

Reducing the temperature slows the reaction down drastically .

Sulphuric acid is used in car batteries, and in the the manufavture of fertilisers, dyes plastics and paints.

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Soaps and detergents contain surfactant moleules which have a hyrdophilic head and a hydrophobic tail.

The surfactant lowers the surface tension of the water. Surfactants also let immiscible liquids mix (like oil and water).

Soaps are made from Carboxylic acids and an Alkali

Soaps form scum in hard water areas, detergents do not. The scum is an insoluable salt.

Biological detergents contain enzymes. Enzymes are biological catalysts. Bio detergents are good because they work at lower temperatures (about 40 degrees C). But you HAVE to use them at cooler temperatures otherwise the ezymes are destroyed. Also cooler temperatures make it harder to remove grease and grime.

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