Page 31 - Big Ideas Year 10 sciPAD 2025

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SCIPAD - BIG IDEAS - BOOK 2
BASIS OF CHEMICAL REACTIONS
What is a Base?
A base is an “acid opposite” and will remove hydrogen ions from a solution.
They are usually metal oxides, metal hydroxides, metal carbonates or metal
hydrogen carbonates. Many bases are insoluble - they do not dissolve in
water. If a base does dissolve in water, we call it an alkali. For example:
•
Copper oxide is a base because it will react with acids and neutralise
them, but it is not an alkali because it does not dissolve in water.
•
Sodium hydroxide is a base because it will react with acids and
neutralise them. It is also an alkali because it dissolves in water.
All alkalis are bases, but only soluble bases are alkalis. Many alkalis release hydroxide (OH-) ions
when they are dissolved in water.
As well as reacting with acids, bases also react with oil and grease and can produce soap. Your
hands are covered in oils that your skin produces naturally. A base on your skin will dissolve those
oils, producing a slippery soap effect - and also burn your skin! (so don’t try this!).
In your home you will have many bases. Because bases are so good at removing grease and oil
we use them as window, drain, bath and oven cleaners. Their ability to remove acid is also useful
and you will find bases in toothpaste (to remove acid caused by plaque), and indigestion tablets
(to remove excess stomach acid).
1. Explain the difference between a base and an alkali? 



2. What happens when a base comes in contact with oil or grease? 

3. What happens to the amount of H+ ions when a base is added to an acid?

4. Suggest why the following household items are usually alkaline:
(a) Oven cleaner: 

(b) Indigestion tablets: 

5. Give four other uses of bases/alkalis around the home.
(a) (b)
(c) (d)
This beaker contains a concentrated alkali as
there are lots of hydroxide ions in the solution.
This one contains a dilute alkali. There is only a
small amount of hydroxide ions in the solution.
Bases are just as dangerous
as acids. They can irritate and
damage your eyes and skin.
Hydroxide
ions (OH-)
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