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H-3
ADVANCE STUDY ASSIGNMENT
1.
Review the previous information on acid-base chemistry.
2.
Review instructions on the use of pH meters. (pages 25 - 27)
3.
A student weighed out 1.111 g of an unknown acid into a beaker and dissolved it using
100.0 mL of deionized water. The titration using NaOH and a pH meter found that 25.52
mL of NaOH was required to reach the equivalence point. How would the equivalence
volume of NaOH, change if the 1.111 g sample had been dissolved in 102.0 mL, or in 200.0
mL of deionized water?
Answer: No change because the moles of acid titrated is unchanged.
4.
If the NaOH used by you in Problem 3 was 0.5555 M, what molar mass should be reported
for the unknown acid?
Answer: 78.37 g/mol
5.
How would you select an indicator that should be used for replicate titrations?
REAGENTS AND APPARATUS
pH meter with electrode
buret (1
only)
standard buffer solutions: pH 4.00 and pH 7.00
indicator solutions (see below)
unknown acid samples
0.50 M HCl (hydrochloric acid)
0.5xx M NaOH (standardized sodium hydroxide)
List of Indicators
Indicator
pH Range
pK
in
Acid
Base
Volume of
Indicator
bromocresol green
3.8 - 5.4
4.7
yellow
blue
5 drops
methyl red
4.2 - 6.2
5.0
red
yellow
5 drops
bromothymol blue
6.0 - 7.6
7.1
yellow
blue
8 drops
cresol red
7.2 - 8.8
8.2
yellow
magenta
4 drops
thymol blue
8.0 - 9.6
8.9
yellow
blue
10 drops
phenolphthalein
8.0 - 9.8
9.4
colorless
pink
3 drops
thymolphthalein
9.5 – 10.5
9.9
colorless
blue
10 drops
