The pH Concept

In my previous post, I posted the definition of acids and bases and the properties of acids and bases. We learned that acids donates H+ ions in solution while bases donates OH- ions in solution.  pH is defined as the measure of acidity and basicity of substance in solution.  pH also measures the  H+ ion concentration in solution.  The range goes from 0 - 14 where pH 0-6 indicates that a solution is acidic,  pH 7 means neutral substances and pH 8-14 indicates basic substances.

Converting [H+] to pH

The pH scale expresses the molar hydrogen ion concentration [H+], as a power of 10.  It means pH is the negative logarithm of the molar hydrogen ion concentration. That is 

Example 1.

What is the pH of the solution if the hydrogen ion concentration, [H+] is 0.1 M?

Solution:

 The easiest way to calculate the concentration in pH is to express the concentration first to the power of 10.  See the calculation below:

The log of  is -1, since we get the - log the pH equals 1.

Example 2.

Calculate the pH of vinegar with hydrogen ion concentration of [H+] 0.001 M.

Solution:

Converting pH to [H+]

We can calculate the hydrogen ion concentration [H+] given the pH by rearranging the equation :

For example, if a solution has a pH of 5, what is the [H+]?  Look at  the solution below:

Just make the value of pH as the exponent and express it in concentration by molarity.

Another example:

Calculate the hydrogen ion concentration of a solution having pH of 4.

Solution:

TRY THIS: