# Analytical Chemistry Problems

See attached file for full problem description.

Please answer the attached questions. Please show detailed work and rationale for the steps to answer the questions.

3. The following is a list of common errors encountered in research laboratories. Categorize each as a determinate or an indeterminate error, and further categorize determinate errors as instrumental, operative, or methodic; (a) An unknown being weighed is hygroscopic; (b) One component of a mixture being analyzed quantitatively by gas chromatography reacts with the column packing; (c) A radioactive sample being counted repeatedly without any change in conditions yields a slightly different count at each trial; (d) The tip of the pipet used in the analysis is broken; (e) In measuring the same peak heights of a chromatogram, two technicians each report different heights.

5. How many significant figures does each of the following numbers have?

(a) 0.02670 (b) 328.0 (c) 7000.0 (d) 0.00200

10. An analyst wishes to analyze spectrophotometrically the copper content in a bronze sample. If the sample weight about 5g and if the absorbance (A) is to be read to the nearest 0.001 absorbance unit, how accurately should the sample be weighed? Assume the volume of the measured solution will be adjusted to obtain minimum error in the absorbance, that is, so that 0.1 < A <1.

12. A batch of nuclear fuel pellets was weighed to determine if they fell within control guidelines. The weights were 127.2, 128.4, 127.1, 129.0, 128.1 g. Calculate (a) the mean (b) the median, and (c) the range.

13. Calculate the absolute error and the relative error in percent and in parts per thousand in the following (see attached file).

14. Replicate water samples are analyzed for water hardness with the following results; 102.2, 102.8, 103.1, and 102.3 ppm CaCO_3. Calculate (a) the standard deviation; (b) the relative standard deviation, (c) the standard deviation of the mean, and (d) the relative standard deviation of the mean.

19. Calculate the absolute uncertainty in the answer of the following (see attached file).

21. Determination of the sodium level in separate portions of a blood sample by ion-selective electrode measurement gave the following results: 139.2, 139.8, 140.1, 139.4 meq/L. What is the range within which the true value falls, assuming no determinate error (a) at the 90% confidence level, (b) at the 95% confidence level, and (c) at the 99% confidence level?

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#### Solution Preview

For your first question you need to be familiar with the definitions in your analytical chemistry class.

Determinite and indeterminite errors differ in that determinute errors are usually preventable.

Hygroscopic material being weighed is a determinute error is a methodic error, you can choose another method to quantify a hygroscopic reactant (titration/standardization for example)

You GC column reacting with a component of a mixture is another determinute error, choose a different column, operational error.

Radiaiton counts are going to shift both higher and lower no matter, indeterminute error.

Needle tip breaking, operative error (determinute)

Measuring heights differently methodic error (determinute).

5a) 4 b) 4 c) 5 d) 3

Look for numbers (zeros mostly) that don't need to be there, if they are present, they ...

#### Solution Summary

This solution involves answers to analytical chemistry problems.