CHEMISTRY 133

Spring, 2014 Homework Set 1

Only Problems in Bold are Submitted for Grading

Set 1.1 - Complete for quiz on Feb. 6

Statistics Calculations (See Chem. 133 Lab Manual pages 3-4):

1.  Download the file HW11.txt. (this gives the time in minutes and the signal in fluorescence units) and transfer to an Excel File.  Print a table from Excel showing two columns collected over the first 30 s period.

2.  Make a plot of the raw data from above and also data processed with a 2 s moving average over both the first 30 s and over the first 4 min.  This can be done by either using Excel's Plotting routines or by creating a 2 s moving average using a new column in Excel.

3.  Given the following data, determine the concentration of chloride in an unknown and the standard deviation in its concentration.

Calibration Data......................................................... Unknown Data

 Cl Conc. Peak Area Cl Conc. mg/mL mg/mL Peak Area 2 0.4516 unknown 9.2133 10 2.4344 20 5.3388 50 15.4836

Statistical Calculations - SOLUTIONS (updated part 2. 2/11 10:30 since original answer used 1.2 s moving average)

From Rubinson and Rubinson:  6.1, 6.2, 6.3, 6.5, 6.6, 6.7

text problem solutions

PDF link to rest of problems

Solutions to other problems (circuit problems not in text)

Homework Set 1.2

Complete for quiz on Feb. 20

From Rubinson and Rubinson:  6.19

Homework Set 1.3

Complete by Feb. 27 (but no quiz planned)

From Rubinson and Rubinson:  6.13, 6.15

1.  Which type of noise is best reduced by shielding the critical electronics?

2.  An instrument measures the concentration of a compound in a river that varies on the order of minutes.  Most of the noise associated with the measurement occurs at frequencies greater than 1 Hz.  Suggest a method (analog or digital) to increase the signal to noise ratio.

3.  What type of noise can be reduced by using internal amplification in a transducer?

4.  What type of noise can be reduced by cooling electrical components?

5.  A sample is measured 12 times by a spectroscopic method.  The average concentration and standard deviation in the average are found to be 5.2+0.7 μM.  With the assumptions made below answer the following questions:

Assume: 1) noise is purely random, 2) the noise is defined as the standard deviation, and 3) that the standard deviation is well-represented.  (The third assumption allows you to avoid using t-factors in signal averaging)

a)  What signal to noise ratio would be expected in a single measurement?

b)  What is the signal to noise in the average value for the twelve measurements?

c)  A researcher needs to have the noise be less than 2% of the value in a particular experiment.  How many measurements should she make?

Harris Text: Ch. 13:      1, 5, 10, 16, 19, 28, 36 [THESE ARE POSTPONED]