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EXAM 1
CHEMISTRY 224
FEBRUARY 7, 2012
1. Read the following instructions carefully
2. Write your name and Purdue ID number on the answer sheet
3. Write your Graduate Instructor’s name on the line for “Instructor” on the answer sheet
4. Use a #2 pencil to
code
all information on the answer sheet.
5.
Code
your name and Purdue ID number on the answer sheet
6.
Code
0224 as the “Section number” on the answer sheet.
7.
Code
the one best answer to each question on the answer sheet.
YOU ARE SUPPOSED TO KNOW (REMEMBER) A NUMBER OF BASIC
EQUATIONS.
ADDITIONAL FORMULAS AND STATISTICAL TABLES ARE
INCLUDED AT THE END OF THE EXAM.
WE STRONGLY SUGGEST THAT
YOU CHECK THE REFERENCE SECTION AT THE END OF THIS BOOKLET
BEFORE YOU START WORKING ON THE EXAM.
ATTENTION:
SOME OF THE QUESTIONS THAT LOOK LIKE THEY REQUIRE
COMPLEX CALCULATIONS CAN ACTUALLY BE ANSWERED BY USING
SIMPLE REASONING AND INTUITION.
THERE ARE 20 REGULAR QUESTIONS PLUS 1 BONUS QUESTION. EACH
QUESTION IS WORTH TEN (10) POINTS. BONUS QUESTION SCORE IS ADDED
TO YOUR TOTAL
*
*
Example: Harry answers 14 regular questions and 1 bonus question. His total for the
exam is 150 points. Jane answers 20 regular questions and 1 bonus question. Her total is
200 points (the total cannot exceed 200).
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View Full Document1.
In lab 2 (“Acid/base titration”), Alice and Bob reported unknown concentration and the
experimental error to be 0.098±0.006M and 0.068±0.023M, respectively. Both Alice and
Bob are good students and reported the error correctly. What can you say about their
results?
a.
Alice’s measurements were more accurate and precise than Bob’s.
b.
Bob’s measurements were more accurate and precise than Alice’s.
c.
Alice’s measurements were more accurate than Bob’s.
d.
Alice’s measurements were more precise than Bob’s.
e.
It is impossible to say anything from these two reported values.
Answer: d. The uncertainty based on repeat measurements refers to random errors and
characterizes the precision (reproducibility) of measurements. It does not address
systematic errors and thus cannot be considered a measure of accuracy.
2.
Craig is making three solutions:
Solution A
: 250 mL of 0.2 M KHP solution using 250 mL volumetric flask with
nominal error of ± 0.10 mL.
Solution B
: 1000 mL of 1 M NaOH solution using 1000 mL volumetric flask with
nominal error of ± 0.30 mL.
Solution C
: 50 mL of 0.001 M KHP solution using 50 mL graduated cylinder with
nominal error of ± 0.05 mL
In which case the relative error in concentration is expected to be highest? In your
analysis, neglect the error associated with weighing masses.
a.
A
b.
B
c.
C
d.
A and B (equally high)
e.
A and C (equally high)
Answer: c. Concentration in M is
( /
)/
c
m MW
V
=
; neglecting errors in
m
, we obtain
//
cc VV
∆=
∆
3.
Alice created a standard acid solution by dissolving 5.087g of KHP (MW 204.23
g/mol) in 250.0 mL of deionized water. Then she titrated a 25.00 mL aliquot of this acid
with 19.28 mL of NaOH solution to reach a pale pink endpoint (determined using
phenolphthalein indicator). Calculate the concentration of NaOH solution in Alice’s
experiment.
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 Chemistry

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