Acid–alkali indicators
3 marks · EasyA student is given a solution and asked to measure its pH using universal indicator.
Describe how the student should use universal indicator solution to estimate the pH of the solution.
Explain how the student can decide on the pH value after adding the indicator.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) Add a few drops of universal indicator to the solution, then observe the colour change and compare it to a pH colour chart.
(b) Compare the colour with a pH colour chart provided with the indicator.
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · Describes adding universal indicator to the solution.
M2 (a) · 1 mark · Mentions observing the colour change or matches colour.
B1 (b) · 1 mark · Explains that the colour is compared to a pH colour chart to estimate pH.
Worked solution
a. The student should add a few drops of universal indicator solution to the test solution. After mixing, note the colour that appears. This colour should be compared to a pH colour chart provided with the indicator. b. By matching the observed colour of the solution to the closest colour on the chart, the student can estimate the pH value.