gcsescience.com                                             24                                           gcsescience.com

Acids and Alkalis

pH.

pH is a measure of how acidic or how alkaline a solution in water is.
The pH scale goes from 1 to 14,
with 1 being very strongly acidic,
and 14 being very strongly alkaline.
A pH of 7 is neutral.

You can measure the pH of a solution using universal indicator.
Just as litmus paper will be red for an acid and blue for an alkali,
so universal indicator is a mixture of indicators
which will give a different colour for a different pH.

Any acid will have a pH of less than 7.
Any alkali will have a pH of more than 7.

A strong acid (HCl or H₂SO₄ or HNO₃ )will have a pH of 1 (red).
A weak acid will have a pH of 3 to 4 (orange).
Examples of weak acids are ethanoic acid (vinegar),
citric acid (lemon juice) and rain water.
Rain water has a natural pH of 5·5 (see carbonic acid).
Water and salts are neutral, pH 7 (green).
A weak alkali (ammonia) will have a pH of 11 to 12 (blue).
A strong alkali (Ca(OH)₂or NaOH) will have a pH of 14 (purple).

       Headings       Acids and Alkalis       Search       Questions      

gcsescience.com                 Contents       The Periodic Table       Index                gcsescience.com

Copyright © 2008 Dr. Colin France. All Rights Reserved.