pH and indicators
3 marks · EasySome students are testing three household substances with universal indicator.
Explain what universal indicator does when added to an aqueous solution.
A solution turns orange with universal indicator. State if this solution is acidic, neutral or alkaline.
Which household substance is likely to give a universal indicator colour of purple? Choose from: vinegar, tap water, sodium bicarbonate solution, bleach.
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) Shows a range of colours to indicate the pH of the solution.
(b) Acidic
(c) Bleach
Common mistakes: orange=alkaline; purple=acid
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Describes universal indicator shows a colour for pH or measures approximate pH by its colour
B1 (b) · 1 mark · States orange means acidic
B1 (c) · 1 mark · Identifies bleach as strongly alkaline (purple with universal indicator)
Worked solution
a. Universal indicator gives a colour that matches to a pH value, showing how acidic or alkaline the solution is.
b. Orange colour is in the acid range, so the solution is acidic.
c. Bleach is strongly alkaline and would turn universal indicator purple.