WorksheetsAP Chemistry Indicators
Total questions: 10
Worksheet time: 15mins
Name
Class
Date
1.
What is the effect on HIn indicator when NaOH is added to it?
a)
Equilibrium shifts to right and more of colour B is seen.
b)
Equilibrium shifts to left and more of colour B is seen.
c)
Equilibrium shifts to right and more of colour A is seen
d)
Equilibrium shifts to left and more of colour A is seen
2.
Bromophenol blue changes from yellow to blue over pH of 3.0 to 4.6. Which statement is correct?
a)
Molecules of bromophenol blue, HIn, are blue.
b)
pH < 3.0, bromophenol blue contain more ion, In–, than HIn.
c)
pKa of bromophenol blue is between 3.0 and 4.6.
d)
Bromophenol blue is suitable to titrate CH3COOH with KOH.
3.
Indicator, HIn is used in titration. Which statement on dissociation of indicator, is correct?
a)
In strong alkaline, colour B would be observed.
b)
In strong acidic, colour B would be observed.
c)
[In–] is greater than [HIn] at equivalence point.
d)
In weakly acidic, colour B would be observed.
4.
Which indicator would be appropriate for titrating weak base, CH3CH2NH2, with nitric acid?
a)
Bromophenol blue (pKa = 4.1)
b)
Bromothymol blue (pKa = 7.3)
c)
Phenol red (pKa = 8.0)
d)
Phenolphthalein (pKa = 9.50)
5.
Which statement about indicators is always correct?
a)
Mid-point of an indicator’s colour change is at pH = 7.
b)
pH range is greater for indicators with higher pKa values
c)
Colour red indicates an acidic solution
d)
pKa value of the indicator is within its pH range.
6.
Acid-base indicator has pKa value of 4.0. At what pH will this indicator change colour?
a)
2
b)
4
c)
8
d)
12
7.
Which could use phenolphthalein (pKa=9.5) and not methyl orange (pKa=3.46) as indicator?
a)
NaOH and HNO3
b)
NH3 and CH3COOH
c)
NaOH and CH3COOH
d)
NH3 and HNO3
8.
Which statement about this indicator is correct?
a)
In a strongly acidic solution colour B would be seen.
b)
In neutral solution, concentration of HIn and In– are equal.
c)
Suitable for titration involving weak acids and weak bases.
d)
None of the above
9.
Which indicator cannot be used for titration curve with a pH jump from (2.7 - 7.8)?
a)
Methyl orange (pKa 3.4)
b)
Methyl red (pKa 5)
c)
Bromothymol blue (pKa 7.3)
d)
Phenol red (pKa 8)
10.
Which of the following statement is FALSE?
a)
Indicators are organic weak acids
b)
Indicators change color at its pKa
c)
End point for indicator must coincide with equivalent point
d)
Indicator change color at a specific pH
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