HMWK 10 FA 2015 - C211 FALL 2015 Homework 10 Name 15 points...

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1 C211 FALL 2015 Homework 10 Name ____________________________ 15 points total . Due Friday Dec. 11, by 5 pm. This assignment will help you study for the final. 1. (1 pt) Statistics: A chemist performed a analysis of 5 replicate samples of NIST traceable certified materials, with these results: iron = 7.82 % + 0.09 % (wt/wt). The NIST certified value was 8.01 % (wt/wt) . Use the appropriate statistical test of significance at 95 % confidence, to show whether or not the analyst found the "true" value. Clearly indicate the criterion value you use. 2. (1 pt) Propagation of Error : Report the moles present in a solution, with its absolute standard deviation , from the volume and concentration data below. Extra digits are shown for calculation purposes. V = 48.23 mL (+ 0.12 mL) C = 1.28 x 10 3 M (+ 0.03 x 10 3 ) M 3. (0.5 pt) Statistics: Which of the following statistical parameters INCREASES the range of accepted values when calculating the confidence interval? a) more samples taken b) greater standard deviation c) higher % confidence level d) greater value of the mean e) greater distance from true mean
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2 4. (1.2 pt) Gravimetry : A sample of elk bone is dissolved in hydrochloric acid, giving 50.0 mL of solution containing calcium as Ca 2+ ion. To precipitate the calcium ion from the resulting solution an excess of potassium oxalate was added. The precipitate of calcium oxalate CaC 2 O 4 weighed 1.437 g. (a) What is the mass of calcium in the original bone sample? (b) What was the molarity of Ca 2+ in the solution? (c) What is the concentration of Ca 2+ in the solution, expressed in ppm? 5. (1 pt) Titration : A sample of impure Na 2 CO 3 (mass = 1.457 g) is dissolved in 50.00 mL water. A 5.00 mL aliquot of this is titrated with 0.01700 M HCl to the methyl red end point, requiring 23.29 mL. What is the composition of the impure sample as % CO 3 2 (wt/wt)?
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