# Exam1_v4_with_answers - EXAM 1 CHEMISTRY 224 FEBRUARY 7...

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1. 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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Exam1_v4_with_answers - EXAM 1 CHEMISTRY 224 FEBRUARY 7...

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