Determining pH

The pH is the measure of the acidic (or basic) power of a solution. It is a scale for measuring hydrogen ion concentration in a solution. The pH scale varies from 0 to 14. At 25 °C (298 K), a neutral solution has a pH equal to 7. A value less than 7 on the pH scale represents an acidic solution. Whereas a pH value of more than 7 represents the basic solution. Generally, a paper impregnated with the universal indicator is used for finding the approximate pH value. It shows different colours at different pH.

In this experiment, we will find the pH value and its nature of the given sample solutions (HCl, NaOH, Vinegar, Lemon juice, Na₂CO₃, Water extract of soil, Distilled water) using the pH paper.

Apparatus and Materials Required

Chemicals

• Dilute hydrochloric acid
• Dilute acetic acid 
• Dilute sodium hydroxide 
• Sodium carbonate solution 
• A fruit juice such as lemon juice
• The soil water extract
• Distilled water

Apparatus

• Beakers
• pH papers

Procedure

The following steps to follow for the procedure:

1. Place seven clean beakers on a table.
2. Take the solutions of dilute acid (say HCl), dilute base (say NaOH), sodium carbonate, vinegar, water extract of soil, distilled water and fruit juice separately in seven beakers and label them. 
3. Put one or two drops of each test solution on different strips of pH paper using a glass rod. Glass rod used for one sample must be washed with water before being used for the other sample. 
4. Note the pH by comparing the colour that appeared on the pH paper with those on the colour chart for the pH paper. 
5. Finally, record the pH values of sample solutions that match the colour on the pH paper.

In this experiment, we learned that:

1. We observed the colour changes on the pH paper for various solutions.
2. The properties of various solutions were studied using a pH scale to see whether the solution was acidic or basic or neutral. It can be concluded that:
3. The nature of HCl, CH₃COOH, Lemon Juice, and the water extract of the soil is found to be acidic. The approximate pH range for these solutions is between 1 and 6.
4. The nature of distilled water was found to be neutral, and the pH value is 7.
5. The nature of NaOH and Na₂CO₃ is found to be basic. The approximate pH range for these solutions is between 10 and 14.

FAQs on Determining pH