Power of Hydrogen (pH) is the measure of acidity or basicity of an aqueous solution. Solutions having pH less than 7 are acidic while solutions having pH more than 7 are said to be basic. Pure water has a pH of 7.

 

 

 

 

 

 

 

 

     pH value can be determined by using the concentration of hydrogen ion [H+]. For example, you are given a compound with a [H+] of 0.1 M, find its pH value and determine if it’s a strong acid, weak acid, neutral, weak base, or strong base.

 

 

 

 

 

 

 

     Simply substitute the given [H+] to the formula and you will now know its pH value. The solution has pH of 1, so it is a strong acid. To make it easier, you can use your scientific calculator and you will obtain the same result (-log[H+]).

     On the other hand, if you are given the pH of a certain solution and you want to know the concentration of hydrogen ion [H+] just plug in the pH value in the formula:

 

 

 

 

 

 

     To make the computation easier, you can also use your calculator by using the antilog times the negative value of the pH and you can get the same results.

     In bases, the concentration of hydrogen ion [H+] is not present; therefore, use the concentration of hydroxide ion [OH-]. Always remember that the sum of pH and pOH is equal to 14.

     For example, you are given the value of [OH-] equal to 0.040; simply substitute it to the formula:

 

 

 

 

 

 

 

                NOTE: The [H+] and [OH-] must always be in molar (M) to find the correct pH or pOH value.