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An Explanation of the PH Scale - Teacher Resource
1.
Pure water is a poor conductor of electricity which proves it has few ions (free electrons). An
ion is an atom or a group of atoms that carries a positive or a negative charge as a result of
having lost or gained one or more electrons. A free electron or other subatomic-charged particle
is also referred to as an ion.
2.
Pure water can be used to measure the ions or pH of a substance dissolved in the water.
Please note that some substances do not dissolve completely, others do.
3.
An acid can be defined as any water-soluble and sour compound capable of reacting with a
base to form salts that are hydrogen-containing molecules that will give up a proton to the base
and accept an unshared pair of electrons from that base.
4.
A base is fundamentals foundation or a main ingredient. It is the starting place and acts upon
the acid. A base is the compound that reacts with the acid to form a salt because the molecules
(ions) are able to take a proton from the acid and share a pair of electrons with the acid. (A salt
consists of positive ions from a base and negative ions from an acid.)
5.
The pH scale can be used to measure acidity or basicity of any water solution by measuring the
ion concentration which is expressed as the concentration of H3O+ (hydronium ions) in powers
of 10, from 10-14 to 10. (Hydronium is a hydrated hydrogen ion. A regular hydrogen ion in water
is expressed as 1420.)
6.
For example, a substance can measure 10-9, which is expressed as -9. By eliminating the
because the scale is logarithmic, we say the pH of the substance is 9.
7.
acid
0
The pH scale is shown graphically as:
neutral
7
base
14
[H30+] |M 1O-7 M
8.
9.
10.
11.
10-14 M
Pure water has a pH of 7. It is neutral.
As the hydronium ion increases as a neutral solution, it is more acidic. The pH goes from 7
toward 0.
If the pH solution falls between 7 and 14, the solution is basic.
A small strip of pH paper (litmus paper) dipped in a solution will test (through the visible change
of color) the pH of most substances.
NOTE:
In foods, acids and bases give distinctive tastes. Acids are sour (lemon juice, vinegar). Bases
are salt (sodium chloride or table salt).