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Understanding the basics of pH

by Tash Hughes of Word Constructions 

pH is one of those words or terms that you are familiar with and hear all over the place, but sometimes arenít quite sure what it really means.

You will hear people talking about the pH of swimming pools, garden soil, skin, chemicals and foods amongst other things.

What does pH mean?

pH is a measure of how acidic or otherwise a solution or substance is. We use a pH scale of 0 to 14 to assess the acidity of various substances.

Pure water is the standard to set the pH scale and has the value of 7. This is known as neutral.

Acidic substances have pH levels below 7 and basic (non acid) substances have pHs greater than 7.

Variations in pH affect animals, plants and inanimate objects.

For instance, at pH 7.5, avocado, corn and mushrooms grow very well but cauliflower, celery and lettuce may not survive. Bilberries and cranberries, on the other hand, like Ph of 4.5.

Swimming pools will ideally have a pH of 7.4 to 7.6. High pH levels in a pool leads to scale formation on the walls, cloudy water and inefficient filter operation whilst low pH leads to metal fittings rusting and stained plaster. Both high and low pH will cause skin and eye irritation for swimmers.

Small variations in pH can have a large effect on the use of a substance. Changing the soil pH of a hydrangea plant will change the flower colour from pink to blue, and changing blood pH out of the normal range (7.3 to 7.52 ) can be life threatening.

Strong acids and bases (such as anything with a pH of 1 or 13) can be very dangerous and reactive.

What is pH?

Unlike many other terms, pH isnít actually an abbreviation; it really refers to the hydrogen ion concentration.

Water is made up of hydrogen and oxygen. At normal temperatures, pure water will break down into some single hydrogen atoms.

Anything that has a much greater number of free hydrogen atoms is known as an acid; fewer hydrogen atoms are found in alkaline substances.

pH is calculated as the by the formula pH = log10 1/[H+]

Due to the nature of log equations, increasing the number of hydrogen atoms actually decreases the pH. So, an acid has many hydrogen atoms and a low pH. Compared to a base with few hydrogen atoms and a high pH.

How do you measure pH?

There are a number of tests available for determining the pH of substances. The simplest test is using litmus (or pH) paper which changes colour when exposed to different pH levels.

Different tests are used for liquids and solids, and they may show different colour results, but they are based on the principle of testing how many hydrogen atoms are present.

In simple terms, if a test shows the substance to be too acidic for your needs than adding a base will neutralise it. Or if the test shows a basic result, adding acid will lower the pH.

Care must be taken when adjusting pH levels as the chemicals used to do so can be dangerous and it is easy to over do it and cause the opposite problem.


Tash Hughes has a science degree and experience in writing technical information in plain English to be easily understood. All technical and business writing needs are met by www.wordconstructions.com.au


This article is available for free use on your web site or in your newsletter.

It must be acknowledged as written by Tash Hughes of www.wordconstructions.com.au and copyright remains the property of Tash Hughes.

Please notify us of your use of this article or to request information on commissioned articles.


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