A student wanted to measure the K sp of calcium hydroxide at a certain temperatu
ID: 825640 • Letter: A
Question
A student wanted to measure the Ksp of calcium hydroxide at a certain temperature. She added 5.00 g of solid calcium hydroxide to 50.0 mL of water, and once the mixture had been allowed to equilibrate and settle she carefully decanted 30.0 mL of the liquid. She then did three trials: in each one she titrated 5.00 mL of this solution with 0.1025 M hydrochloric acid. Her first two titrations required almost identical amounts of acid, but the third was slightly lower than the other two. If we assume that it was the third trial that was wrong, match the following proposed sources of error with their critique.
A.
This would cause the titration amount to be too big, not too small.
B.
This would not have affected the final amount of acid needed for the titration.
C.
As it is currently stated, this explanation is chemically impossible.
D.
This mistake would plausibly explain the observed error.
E.
This would have thrown off all three trials, not just the last one.
MATCH A,B,C,D,E WITH THE FOLLOWING:
1. Since the solution for the final titration was sitting the longest, its Ksp value might have changed over time.
2.Small amounts of solid calcium hydroxide might have found their way into the third titration flask without her knowledge.
3.She might have made a mistake when making the acid solution, so that it was more concentrated than she wanted.
4.When refilling the buret for the third titration, she might have accidentally filled it beyond the zero mark and not realized it.
5.The flask into which she put the 5.00 mL of solution for the third trial of the titration might have had some water, which she did not notice.
A.
This would cause the titration amount to be too big, not too small.
B.
This would not have affected the final amount of acid needed for the titration.
C.
As it is currently stated, this explanation is chemically impossible.
D.
This mistake would plausibly explain the observed error.
E.
This would have thrown off all three trials, not just the last one.
MATCH A,B,C,D,E WITH THE FOLLOWING:
1. Since the solution for the final titration was sitting the longest, its Ksp value might have changed over time.
2.Small amounts of solid calcium hydroxide might have found their way into the third titration flask without her knowledge.
3.She might have made a mistake when making the acid solution, so that it was more concentrated than she wanted.
4.When refilling the buret for the third titration, she might have accidentally filled it beyond the zero mark and not realized it.
5.The flask into which she put the 5.00 mL of solution for the third trial of the titration might have had some water, which she did not notice.
Explanation / Answer
A - 4
B - 1
C - 2
D - 5
E - 3
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