| Aim | To determine the pH of various solutions using pH paper or universal indicator, to compare the pH of solutions of strong and weak acids of the same concentration, and to study the pH change in the titration of a strong acid with a strong base. |
| Apparatus Required | pH paper or universal indicator Solutions of known and varied concentrations of acids, bases, and salts Distilled water NaOH (0.1 M) HCl (0.1 M) CH3COOH (0.1 M) NH4OH (0.1 M) Fruit juices (orange, lemon, grapefruit, etc.) Beakers Stirring rods Burette Pipette |
| Theory | pH is a measure of the acidity or basicity of a solution. It is defined as the negative logarithm of the hydrogen ion concentration (pH = -log[H+]). A solution with a pH of 7 is neutral, while a solution with a pH below 7 is acidic and a solution with a pH above 7 is basic. The pH of a solution can be determined using pH paper or a universal indicator, which changes color depending on the pH of the solution. In this experiment, we will use pH paper or a universal indicator to determine the pH of various solutions, including solutions of known and varied concentrations of acids, bases, and salts, as well as fruit juices. We will also compare the pH of solutions of strong and weak acids of the same concentration and study the pH change in the titration of a strong acid with a strong base. |
| Procedure | Label five beakers A, B, C, D, and E. In beaker A, add 10 mL of distilled water and test the pH using pH paper or universal indicator. In beaker B, add 10 mL of 0.1 M HCl and test the pH using pH paper or universal indicator. In beaker C, add 10 mL of 0.1 M NaOH and test the pH using pH paper or universal indicator. In beaker D, add 10 mL of 0.1 M CH3COOH and test the pH using pH paper or universal indicator. In beaker E, add 10 mL of 0.1 M NH4OH and test the pH using pH paper or universal indicator. Repeat steps 2-6 with solutions of different concentrations of acids, bases, and salts. Take 10 mL of each fruit juice and test the pH using pH paper or universal indicator. Label two beakers F and G. In beaker F, add 10 mL of 0.1 M HCl and test the pH using pH paper or universal indicator. In beaker G, add 10 mL of 0.1 M CH3COOH and test the pH using pH paper or universal indicator. Add 1 mL of 0.1 M NaOH to beaker F and stir. Test the pH using pH paper or universal indicator. Add 1 mL of 0.1 M NaOH to beaker G and stir. Test the pH using pH paper or universal indicator. Repeat steps 12-13 until the pH of beaker F reaches 7. Record the volume of NaOH added to beaker F and the corresponding pH values. Repeat steps 12-13 with beaker G, but record the volume of NaOH added to reach a pH of 8. Label two beakers H and I. In beaker H, add 10 mL of 0.1 M H |
| Observation and Results | Determination of pH of various solutions: Distilled water: pH 7 (neutral) 0.1 M HCl: pH < 7 (acidic) 0.1 M NaOH: pH > 7 (basic) 0.1 M CH3COOH: pH < 7 (weakly acidic) 0.1 M NH4OH: pH > 7 (weakly basic) Solutions of different concentrations of acids, bases, and salts: pH values varied depending on the concentration and type of solution Fruit juices: pH values varied depending on the type of fruit juice (b) Comparing the pH of solutions of strong and weak acids of the same concentration: Beaker F (0.1 M HCl): pH < 7 Beaker G (0.1 M CH3COOH): pH < 7 As NaOH was added to beaker F, the pH gradually increased until it reached 7, indicating neutralization of the acid by the base. As NaOH was added to beaker G, the pH gradually increased but did not reach 7, indicating that weak acids are not completely neutralized by strong bases. (c) Study of pH change in the titration of a strong acid with a strong base: Beaker H (0.1 M HCl): pH < 7 Beaker I (unknown concentration of HCl): pH < 7 NaOH was added to beaker I until the pH reached 7, indicating neutralization of the acid by the base. The volume of NaOH added was recorded and used to calculate the concentration of HCl in beaker I using the equation: M1V1 = M2V2 where M1 = concentration of NaOH (0.1 M), V1 = volume of NaOH added to beaker I, M2 = concentration of HCl in beaker I, and V2 = total volume of the solution in beaker I. Overall, this experiment demonstrated the relationship between pH and the concentration and type of solution, as well as the differences between strong and weak acids in their reaction with strong bases. It also showed how the pH of a solution changes during a titration with a strong acid and a strong base, allowing for the determination of the concentration of the acid. |