Name:_____________
Chemistry 232
First Hour Exam
1A. (10 points) I am making a dilute iron standard solution with a concentration of 40 mg/L. I
am starting with a stock solution that is 4.00 (±0.1%) mg/ml in concentration. I will add 1 mL of
that solution to a 100 mL volumetric flask. Assuming these error in filling the pipet is ± 0.05 mL,
and the error in filling the volumetric flask is ±0.05 mL, what is the uncertainty in the
concentration of the standard solution?
B (5 points) Write the above concentration with the appropriate number of significant figures.
2. (5 points) What is the difference between random and systematic error.
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3. In the set of data : 1,3,5,6,6,7,9
What is the mean (3 points)?
What is the median (3 points)?
What is the mode (4 points)?
4. (10 points) I have done 8 experiments to determine the amount of iron in a vitamin supplement
tablet. If I report the amount of iron as 25 ± 4 mg/ml using a 95 % confidence interval, what was
the s of for my experimental data.
5. (10 points) I have student who has a 95 on his 1st exam, a 98 on his 2nd exam, a 93 on his 3rd
exam, and a 68 on his 4th exam. Can I use the Q-test to throw out his 4th exam, and give him a
grade based on the other three exams? (I wouldn’t take this problem too seriously!)
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6. (10 points) What is an internal standard? Where and why is it used in an analytical procedure?
7. (10 points) Chloroacetic acid (ClCH2COOH) has a Ka of 1.35x10-3. What is the )G for the
reaction ClCH2COOHW H+ + ClCH2COO-. (Assume T = 35o C)
8. A (10 points) What is the [Zn2+] in a saturated solution of Zn(OH)2 ? (The Ksp for Zn(OH)2 is
2.0 x10-16)
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B (10 points) What is the [Zn2+] in a saturated solution of Zn(OH)2 after I have added enough
NaOH to make the solution 0.01M in OH- (pH 12) ?
C (10 points) What is the [Zn2+] in a saturated solution of Zn(OH)2 after I have added enough
HCl to make the pH 2 ? (Hint: remember the equilibrium between H+ and OH- in water. Don’t be
surprised if your answer looks funny)
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