Acids, Alkalis and Titrations
5 marks · EasyVinegar and household ammonia are tested using two different indicators:
State which solution is acidic and which is alkaline.
A drop of vinegar is placed on blue litmus paper. Describe what is observed.
Household ammonia is tested with universal indicator. Name the colour you would expect and explain what this indicates about its pH.
Explain how universal indicator is used to measure the pH of a solution.
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.
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(a) Vinegar is acidic, household ammonia is alkaline.
(b) The blue litmus paper turns red.
(c) Universal indicator turns blue or blue-green in ammonia, showing it is alkaline and has a pH above 7.
(d) Add universal indicator to the solution and compare the resulting colour to a pH chart to find the pH.
Common mistakes: mixing up acidic and alkaline; mixing up indicator colours
Show mark scheme and worked solution
Marking points
A1 (a) · 1 mark · Correctly identify vinegar as acidic and ammonia as alkaline.
A2 (b) · 1 mark · Blue litmus turns red with vinegar (acidic solution).
B1 (c) · 1 mark · Identifies blue (or blue-green) as the expected universal indicator colour in ammonia OR states pH above 7 clearly.
B2 (c) · 1 mark · Explains that this shows ammonia is alkaline or gives correct pH range.
A3 (d) · 1 mark · Describes correct process for using universal indicator to measure pH (add and compare colour to chart).
Worked solution
a. Vinegar is acidic, and household ammonia is alkaline.
b. Blue litmus paper turns red when vinegar (an acid) is added.
c. Universal indicator turns blue or blue-green in household ammonia, showing it is alkaline with a pH greater than 7.
d. To measure pH using universal indicator, add the indicator to the solution, then compare the colour produced to a pH colour chart to read the pH value.