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CH 223
Quantitative Analysis
Exam 1
September 18, 2002
1 _______ (of 20)
2 _______ (of 10)
3 _______ (of 4)
4 ______ (of 10)
5 _______ (of 6)
Extra Credit ______ (of 5)
Σ_____ (Σ_____ (Σ_____ (Σ_____ ( of 50)
Name: ___________________________________________ (please print)
SSN: * * * - * * -________
(last 4 digits)
- Quinine may be determined by measuring the fluorescence intensity in 1 M H 2 SO 4 solution. Standard solutions of quinine gave the following fluorescence values. concentration of quinine x (μg mL -1) 0.00 0.10 0.20 0.30 0. Fluorescence intensity y (arb. units) 0.00 5.20 9.90 15.30 19.
a. Calculate by the least squares method the equation of the best straight line for the calibration curve. Report you result in the form y = [m(±s (^) m )]x + [b(±s (^) b)]. (15 points)
b. An unknown quinine sample gave a fluorescence intensity of 10.20. Calculate the number of quinine in μg/mL in the unknown and estimate its uncertainty. (5 points)
- Analysis of a sample of iron ore gave the following percentage values for the iron content: 7.08, 7.21, 7.12, 7.09, 7.16, 7.14, 7.07, 7.14, 7.18, 7.11. Calculate the a) mean, b) standard deviation and c) coefficient of variation for the values. (4 points)
- To measure the nickel content in steel, the alloy is dissolved in 12 M HCl and neutralized in the presence of citrate ion, which maintains iron in solution. The slightly basic solution is warmed, and dimethylglyoxime (DMG) is added to precipitate the red DMG-nickel complex quantitatively. The product is filtered, washed with cold water, and dried at 110 ºC.
Ni2+^ + 2
N
OH
N OH
N
O
N O
N
O
N O
Ni
H
H
FM 58.69 (^) DMG FM 116.
Bis(dimethylglyoximate)nickel(II) FM 288. If the nickel content is known to be near 3 wt % and you wish to analyze 1.0 g of the steel, what volume of 1.0 wt% alcoholic DMG solution should be used to give a 50% excess of DMG for the analysis? Assume that the density of the alcohol solution is 0.79 g/mL. (10 points)
Extra Credit Multiple Choice (5 points total) Circle only one answer, otherwise no extra credit will be given.
- In selecting a substance to serve as a primary standard, which always is essential? a. The substance must have a high equivalent weight. b. The substance must be a strong acid or base. c. The substance must be readily available. d. The substance must have an accurately known purity.
- A calibration curve is required in an analytical procedure when a. no primary standard is available. b. there is no apparent mathematical function relating the quantity sought to the instrument reading. c. the theory of the procedure is unusually complicated. d. utmost precision is required.
- The Student-t test may be used to compare mean values of two sets of data at a predetermined probability level. The name of this comparison is the Null- Hypothesis. If the hypothesis fails the analyst can a. look for determinate errors in one set of data. b identify the poor set of data and discard it. c. conclude that there is a difference in the mean value of the two sets of data at the level compared for each set. d. conclude both sets of data conform to the Normal Error Law.
- Which of the following statements is always correct? a. Accurate data do not fluctuate appreciably. b. Precise data are always accurate c. There is always a determinable absolute true value for all analyses that are performed. d. All data exhibit some degree of fluctuation.
- Which is an essential requirement in order that a reaction be suitable as a quantitative titration. a. A visual indicator must be available for signaling the arrival of the equivalence point. b. The reaction must be at least 99.9% complete. c. The reaction must not require more than five minutes to reach equilibrium. d. The end point must correspond exactly to the equivalence point.
