Self assessment
Question 1 of 6
Which of the following statements are false
a
The equivalence point is when a stoichiometric amount of titrant has been added to the titrated substance.
b
The equivalence point is another name for the end point of a titration.
c
The equivalence point is where a titration should really end and a suitable indicator will change colour close to this point.
d
The end point of a titration is where a definite change, such as a change of colour, is observed.
The pKIn is 3.7 for methyl orange indicator. What does this tell you?
A
Above pH 3.7 the indicator looks yellow.
B
Below pH 3.7 the indicator looks red.
C
At about pH 3.7 half of the indicator is present as HIn and half is present as In–. This looks orange.
D
Below pH 3.7 the indicator looks yellow.
How would you, the teacher, respond to a student who can’t see why different indicators are required since universal indicator can ‘cover a whole range’?
A
Universal indicator produces a wide range of colours across the pH scale which are quite gradual.
B
We use a single indicator when carrying out a titration requiring a sharp colour change at the equivalence point, while universal indicator only gives slow colour changes.
C
I explained all this last week. Weren't you listening?
D
For a titration you need a single indicator for with a pKa the same as the acid in the titration
In a titration of and acid and an alkali, what can you correctly say about the equivalence point?
A
Depending on the acid & alkali chosen, the equivalence point is never at a neutral pH.
B
Depending on the acid and alkali chosen, the equivalence point always occurs at pH 7.
C
Depending on the acid and alkai chosen, the equivalence point may or may not occur at the neutral point. We need an indicator that changes colour at a pH very close to the equivalence point
D
Depending on the acid and alkali chosen, some of the products formed may be acidic or alkaline, meaning that some reactions have different equivlence points, and a selection of indicators is required with different ranges.
The following table shows data for two common indicators. What colour will each show at pH 6.5?
| indicator | pKIn | colour (low pH) | pH range | colour (high pH) |
| methyl red | 5.1 | red | 4.8 – 6.3 | yellow |
| bromothymol blue | yellow | 6.0 – 7.6 | blue |
A
Methyl red will be yellow; bromothymol blue will be green
B
Methyl red will be yellow; bromothymol blue will be blue
C
Methyl red will be orange; bromothymol blue will be green
D
Methyl red will be red; bromothymol blue will be yellow
Choose a suitable indicator for the titration of potassium hydroxide and ethanoic acid.
A
Methyl orange
B
Methyl red
C
Bromothymol blue
D
Phenolphthalien