Teacher Resource 1
Introduction
Indicators are best taught alongside titration curves by using visual representations of the colours of
the indicators on top of each of the titration curves. This activity is best done after learners have
performed the various combinations of titrations and used the indicators. Alternatively, this could
form part of a wider research activity about characteristics of pH titrations, in which case learners
may come up with less ‘standard’ examples of indicators.
Colours on graphs are depicted in textbooks in two different ways, which can confuse learners. Stick
to colouring the entire section of the graph in the appropriate colour that the solution would be with
the presence of that indicator, e.g. in a titration curve with phenolphthalein

colour the top part of the graph, from pH 10–14, pink

make the section between pH 10–8.3 a gradient of pink to white and label as ‘the pH range
of phenolphthalein’

leave everything beneath pH 8.3 white.
This will show what colour the solution will be at the various pHs and the pH range at which it will
change.
Expected answers for worksheets
Strong alkali added to strong acid
The equivalence point is in the middle of the pH scale.
Indicators: A wide range of indicators would be suitable as the vertical section of the curve is large.
Phenolphthalein and methyl orange are likely to be mentioned if learners are working from a
standard textbook.
pH range labelled on graph, e.g.

for methyl orange: 3.1–4.4

for phenolphthalein: 8.3–10.
Strong alkali added to weak acid
The equivalence point is high on the pH scale.
Indicator: Phenolphthalein (or other suitable indicator in pH range 7–10).
pH range labelled on graph, e.g. for phenolphthalein: 8.3–10.
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pH and Buffers
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Weak alkali added to strong acid
The equivalence point is low on the pH scale.
Indicator: Methyl orange (or other suitable indicator in pH range 3–6).
pH range labelled on graph, e.g. for methyl orange: 3.1–4.4.
Weak alkali added to weak acid
The equivalence point is in the middle of the pH scale.
Indicator: There is no suitable indicator, as there is no clear vertical section in the titration curve.
No pH range labelled on graph, as no suitable indicators.
OCR Resources: the small print
OCR’s resources are provided to support the teaching of OCR specifications, but in no way constitute an endorsed teaching method that is required by the Board, and the decision to
use them lies with the individual teacher. Whilst every effort is made to ensure the accuracy of the content, OCR cannot be held responsible for any errors or omissions within these
resources.
© OCR 2016 - This resource may be freely copied and distributed, as long as the OCR logo and this message remain intact and OCR is acknowledged as the originator of this work.
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© OCR 2016