The name and symbol, pH, stands for
per hydron, per hydrogen or
power of the hydrogen
Acidity is caused by hydrogen atoms that have lost their electrons and are roaming free in water [H+].
The opposite of acidic is alkaline (or basic).
Alkaline gets its name from the "al kali" plant whose ashes are capable of neutralizing acids.
It does this because it contains KOH.
The "OH" is called hydroxide and it combines with the acid [H+] to form water.
We are able to test the acidity or alkalinity of a substance with litmus paper or a litmus solution.
pH is a measure of the acidity or alkalinity of a solution. Aqueous solutions at 25°C with a pH less than seven are considered acidic, while those with a pH greater than seven are considered basic (alkaline).
When a pH level is 7.0, it is defined as 'neutral' at 25°C.
Litmus was used for the first time about 1300 AD by Spanish alchemist Arnaldus de Villanova .
From 16th century on the blue dye was extracted from some lichens, especially in the Netherlands.
The cabbage juice that we are going to use is called an indicator and is the same as the litmus paper we use.
How to make and use the red cabbage litmus solution
- Rip or cut some red cabbage leaves into small pieces
- Place in a bowl and poor boiling water over so that it is more than covered.
- Leave for a half hour or so then separate the solution from the water. You can use a sieve or filter paper.
- Place your solution in a clean, lidded jar.
The resultant solution will be somewhat crude as we have used only plain tap water and done nothing about purifying the equipment.
It will be good enough for our initial experiments though.
- Get four clean jars and put some tap water in each of them
- Place a teaspoon of bicarbonate of soda in one, vinegar in another and lemon juice in a third. With the forth, if it ever happens, collect some rain water
- Put a few drops of solution into each jar and note any colour change
- If the mixture turns pink it is an acid, if it turns green or blue it is a base/alkaline