Oct.18, 2004 Analytical Chemistry
1.Explain the following terms:(18%)
a)peptization b)coagulation
c)Fajans method d)systematic error
e)internal standard f)F-test
2.Estimate the absolute standard deviation for the following calculations.
Round the result to include only significant figures. (4%)
1.43(±0.02)x10^-2 -4.76(±0.06)x10^-3
Y=------------------------------------------
24.3(±0.7)+8.06(±0.08)
=2.948x10^-4
3.a)At what condition, the method of standard addition should be used for the
quantitation? b)Describe it with the graphical method. c)Why is it desirable
to add a small volume of concentrated standard rather than a large volume of
dilute standard? (8%)
4.A prosecuting attorney in a criminal case presented as principal evidence
small fragments of glass found imbedded in the coat of the accused. The
attorney claimed that the fragments were identical in composition to a rare
Belgium stained glass window broken during the crime. The average of
triplicate analyses for five elements in the glass is shown below. On the
basis of these data, does the defendant have grounds for claiming reasonable
doubt as to guilt? Employ the 99% confidence level as a criterion for doubt.
(12%)
Concentration,ppm Standard
------------------------------ Deviation
Element From clothes From window s→σ
--------------------------------------------------------------
As 129 119 9.5
Co 0.53 0.60 0.025
La 3.92 3.52 0.20
Sb 2.75 2.71 0.25
Th 0.61 0.73 0.043
--------------------------------------------------------------
5.How is a control chart used? (6%)
6.In general, we can classify the particle size as precipitate, colloidal and
true solution. Please describe the mechanism of precipitate formation? At
what condition you can get a precipitate, and what factors would determine
the particle size of precipitates? Please illustrate a diagram to show all of
your thinking? (10%)
7.Neohetramine, C16H21ON4(285.37g/mol), is a common antihistamine. A 0.1247g
sample containing this compound was analyzed by the Kjeldahl method. The
ammonia produced was collected in H3BO3; the resulting compound was titrated
with 26.13ml of 0.01477M HCl. Please write the equations involved in the
whole process and calculate the percentage of neohetramine in the sample.
(12%)
8.Describe an argentometric method for the Volhard determination of chloride
ion. (12%)
9.Consider the titration of 50.00ml of a solution that is 0.0500M in iodide ion
and 0.0800M in bromide ion with 0.1000M silver nitrate. Please calculate the
percentage of iodide unprecipitated at the onset of silver bromide
precipitation. (Note:Ksp for AgI is 8.3x10^-17; Ksp for AgBr is 5.0x10^-13)
(12%)
10.Find the molar solubility S of silver chloride in 0.01M potassium nitrate.
The activity constant Ksp。=1.765x10^-10 (12%)
11.Please illustrate the spectrophotometric titration curve for each of the
following conditions. (12%)
a)εs=εp=0,εt>0 b)εp>0,εs=εt=0
c)εs>0,εp=εt=0 d)εs>εt>0,εp=0
e)εt>εp>0,εs=0 f)εp>εt>0,εs=0
另附table of Values of Student's t
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