Acids and alkalis
In this Revision Bite you will revise some important information about acids and alkalis.
Non-metal elements can react with oxygen to form compounds called
S(s) + O2(g) → SO2(g)
(sulphur + oxygen → sulphur dioxide)
Non-metal oxides which dissolve in water produce acid [acid: A corrosive substance which has a pH lower than 7. Acidity is caused by a high concentration of hydrogen ions.] solutions.
SO2(g) + H2O(l) → H2SO3(aq)
(sulphur dioxide + water → sulphurous acid)
Alkaline [alkali: A base which is soluble in water.] solutions are made when soluble metal oxides or metal hydroxides dissolve in water.
Na2O(s) + H2O(l) → 2NaOH(aq)
(sodium oxide + water → sodium hydroxide)
Here are some acids and alkalis that you may recognise.
Video: Acidic, alkaline or neutral
Here is a typical Standard Grade question. Use the information above to help you answer it. Look at the answer after you have tried to do it.
The grid shows compounds that dissolve in water
Identify the two compounds which produce alkaline solutions.
Hint: Think - what type of compound dissolves in water to produce alkaline solutions.
A - potassium oxide
B - calcium oxide
Both potassium oxide and calcium oxide are examples of soluble metal oxides which dissolve in water to produce alkaline solutions. Check your data book for solubilities.
The question quite clearly asks you to give two answers. Do not give any more than two.
This question is worth only one mark and both correct answers must be stated to be awarded one mark.
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