Activity 6.3:
Aim: To study the relationship between the pH value and the strength of an acid and alkali.
Materials: pH paper, 0.1 M hydrochloric acid, sodium hydroxide solution, 0.1 M ethanoic acid, ammonia solution, pH chart and salt solution
Apparatus: Measuring cylinder, test tube and test tube rack
Instruction
1. Pour 2 ml of hydrochloric acid into a test tube.
2. Test the substance in the test tube with a pH paper.
3. Observe the colour change of the pH paper and compare it with a pH chart to determine the pH value.
4. Record your observation in a table.
5. Repeat steps 1 to 4 by replacing hydrochloric acid with the other substances.
Observation
Questions
1. Relate the strength of acid to the pH value.
2. Identify the substance which is a:
(a) strong acid
(b) strong alkali
(c) weak acid
(d) weak alkali
(e) neutral solution
3. Predict the pH value of rain water in an industrial area. Explain your answer.
Answer:
1. Strong acid has low pH value.
2. (a) Hydrochloric acid
(b) Sodium hydroxide solution
(c) Ethanoic acid
(d) Ammonia
(e) Salt water
3. The pH value is below 7 because acidic gases emitted from the factory will dissolve in rain water. Thus, the rain water will become acidic.
Aim: To study the relationship between the pH value and the strength of an acid and alkali.
Materials: pH paper, 0.1 M hydrochloric acid, sodium hydroxide solution, 0.1 M ethanoic acid, ammonia solution, pH chart and salt solution
Apparatus: Measuring cylinder, test tube and test tube rack
Instruction
1. Pour 2 ml of hydrochloric acid into a test tube.
2. Test the substance in the test tube with a pH paper.
3. Observe the colour change of the pH paper and compare it with a pH chart to determine the pH value.
4. Record your observation in a table.
5. Repeat steps 1 to 4 by replacing hydrochloric acid with the other substances.
Observation
Questions
1. Relate the strength of acid to the pH value.
2. Identify the substance which is a:
(a) strong acid
(b) strong alkali
(c) weak acid
(d) weak alkali
(e) neutral solution
3. Predict the pH value of rain water in an industrial area. Explain your answer.
Answer:
1. Strong acid has low pH value.
2. (a) Hydrochloric acid
(b) Sodium hydroxide solution
(c) Ethanoic acid
(d) Ammonia
(e) Salt water
3. The pH value is below 7 because acidic gases emitted from the factory will dissolve in rain water. Thus, the rain water will become acidic.