 The
Open Door Web Site |
|||||||||||||||||||||
|
The pH Scale
The pH scale is used to measure how acidity and alkalinity. Something which is neither acid nor alkaline is said to be neural. The neutral pH is pH7. Distilled water is neutral.
Any pH value below pH7 is acid. Weak acids will be around pH6 or pH5. Strong acids will show pH1 or pH2 when tested. Alkalis how a pH value above pH7. Weak alkalis are around pH8 or pH9. Strong alkalis will have a reading of pH13 or pH14. What is an acid?
You normally have a good idea about acids because
of the taste of vinegar and lemon juice, for example. These
solutions taste sour and can hurt if they touch a cut in your
mouth or your hand. Strong acids are corrosive and they can
‘eat’ through metal. There are many examples of weak acids
in our everyday lives. Rainwater is slightly acidic because it
has carbon dioxide gas dissolved in it. Fizzy drinks are
acidic for the same reason (and bad for your teeth if you
drink too many of them!). You will not often come into contact
with strong acids, fortunately. A car battery contains
concentrated acid (pH1 or pH2) and you might be surprised to
know that your stomach produces an acid at pH2 which helps you
to digest your food
What is
an alkali? How to test pH
You can test the pH of a solution using indicator paper or indicator liquid. An indicator is a chemical which will change colour as the pH changes. There are quite a few indicators in use in the laboratory. This is why each type of indicator paper comes with its own colour chart. When you use indicator liquids, such as universal indicator or bromothymol blue, you are always given pH standards for these solutions to compare your results to. |
|
|||||||||||||||||||
