pH Scale

This site is about five different inorganic chemistry subjects related to pH.

Basic concepts – the pH scale

pH can be measured by a hydrogen sensitive electrode or a pH meter. pH is defined as the negative base 10 logarithm of the hydrogen ion activity{H+}, and not the hydrogen ion concentration [H+]:

pH = -Log10{H+}

Topic: Ideal Gas Law

Ionic Strength

There’s a consensus among chemistry teachers that students should be taught that pH = -Log10[H+] until they reach universitylevel where they are told (at least at chemistry departments) the truth that pH = -Log10{H+}.

If you read this and have been told that pH = -Log10[H+] please keep on reading. You will still be able to learn from the informationprovided here at pH scale.

In the section about ionic strength there are examples and discussion about how [H+] is calculated from {H+} and why it is importantto be able to do so in some situations.

Topic: Equilibriums

The pH scale

The pH scale

The range of the pH scale is from 0 to 14. The pH of a 1 mol/L HCl is solution is approximately 0 (because of ionic interactions between H2O,H+ and Cl, the pH is not exactly 0 – see the ionic strength section). Any solution with a pH less than 7 is by definitionacidic.

Alkaline or basic solutions are those with a pH above 7. while neutral solutions have a pH of exactly 7.

Below is a picture of a scale showing pH from 0 to 14 with examples of solutions with different pH levels:

Topic: pKa & Ka

The basics

Figure: The pH values of the shown solutions are approximate. E.g. the pH of seawater is usually from 7.5 to 8.4.

There are much more than discussions about the pH scale at this webpage, so please take your time to read or download the pdf files or read the webpages.

PDF library

Note:Discussions about the pdf documents are found in the 'Help & Discussions' section.Inorganic chemistry subjects:Equilibriums 1 :A tutorial about how… Read More

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Ions and compounds

Atoms are made up of neutrons that are neutral and have no charge, protons with a positive charge andelectrons with… Read More

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Buffers

BackgroundAs shortly explained in the section about how to calculate pH in a solution of dissolved NaHCO3abuffer has the capability… Read More

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Buffers and Equilibriums

As shortly explained in the section about how to calculate pH in a solution of dissolved NaHCO3, a buffer has… Read More

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An introduction to Ionic Strength

BackgroundTo quantify the effect of inter-ionic interactions, such as molecular attraction and repelling, one has to have a `parameter` describing… Read More

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Gases – the ideal gas law explained

Chemical compounds in aqueous solutions are fairly easy to handle as their quantities can either be expressed in weight such… Read More

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pKa and Ka

Background informationThe Kavalue is a value used to describe the tendency of compounds or ions to dissociate. The Kavalue is… Read More

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NaHCO3 dissolved in water – how is pH calculated?

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pH meter pH strips

BackgroundpH meters have been used since 1936 when they were invented by the Danish company Radiometer.In contrast to many other… Read More

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Question about acetate buffer

This is the long and computational answer to Debra's question about what happens when 100 mmol of HCl ispoured into… Read More

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