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11 January 2017

pH Scale

 

pH is the measure of the acidity or alkalinity of an aqueous solution. Solutions with a pH less than 7 are acidic and solutions with a pH greater than 7 are alkaline. Pure water has a pH very close to 7.

 

Solutions of acids and alkalis can vary widely in their acidity and alkalinity. It is useful to know not just whether a solution is an acid or an alkali, but how acidic or how alkaline it is. Acidity and alkalinity are measured using the pH scale.

The pH scale runs from pH 0 to pH 14. pH Measure of acidity (0-6) or alkalinity (8-14).

< 1 1,5 - 4 4 - 6 6,8 - 8,5 8,5 - 11 11 -13 > 13
             
strong acid acid weakly acidic neutral weakly alkaline alkaline strongly alkaline

Acidic

Chemical substances, compounds, mixtures that have an excess of H+ (Hydrogen) ions. When measured on a pH meter give a reading of 0 to 6. The lower the number, the more H+ ions and the stronger the acid. Organic acids (fruit) typically have a pH of 4 - 6.

Neutral

Pure water is pH neutral.

It has one H+ ion (Hydrogen) and one OH- ion (Hydroxide) = H2O.

Neutral chemical substances, compounds, mixtures when the OH- and H+ ions are in balance. Neutral substances have pH of 7.

Alkaline

Chemical substances, compounds, mixtures that have an excess of hydroxide ions (OH-). When measured on a pH meter give a reading of 8 to 14. The higher the number, the higher the concentration of the ions.

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