In water, acids form positively charged hydrogen ions (H⁺), which makes the solution acidic. On the other hand, alkalis form negatively charged hydroxide ions (OH⁻) in water, which makes the solution alkaline. This can be seen in examples such as:
The pH Scale is a numerical scale that measures how acidic or alkaline a solution is.
The pH scale is based on the concentration of hydrogen (H⁺) and hydroxide (OH⁻) ions. The higher the concentration of hydrogen ions, the lower the pH level of the solution. So, a pH level of 1 would indicate the highest concentration of hydrogen ions.
In contrast, solutions with higher concentrations of hydroxide ions have higher pH levels. The highest pH level is 14, which indicates the highest concentration of hydroxide ions.
The pH of a solution can be measured using an indicator or a pH meter.
Indicators are substances that are used to test whether a solution is acidic or alkaline. Two common indicators are universal indicator and litmus paper.
Universal indicator is an acid-alkali indicator that gives a more precise measurement of pH. It produces a range of colours that can be compared to a colour chart to determine the pH of a solution.
When performing acid-base reactions, we can use universal indicators to determine when the reaction has reached a neutral state. If neutralisation has occurred, the solution should change to a green colour.”
Litmus paper is a strip of paper that has been treated with a mixture of dyes. There are two types of litmus paper:
Litmus paper is a quick and easy way to test the pH of a solution, but it is not as precise as universal indicator.
A pH meter is a more precise and accurate way to determine the acidity or basicity of a solution compared to using a universal indicator. When placed in a solution, the pH meter provides a numerical value indicating the solution’s acidity or basicity.
For example, if the reading is 2, the solution is acidic. The numerical data provided by the pH meter is more accurate than the colour-based method of using a universal indicator.