Principles of Instrumental Analysis
7th Edition
ISBN: 9781305577213
Author: Douglas A. Skoog, F. James Holler, Stanley R. Crouch
Publisher: Cengage Learning
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Chapter 9, Problem 9.22QAP
The chromium in an aqueous sample was determined by pipetting 10.0 ml. of the unknown into each of five 50.0-mL volumetric flasks. Various volumes of a standard containing 12.2 ppm Cr were added to the flasks,
following which the solutions were diluted to volume.
Unknown,mL Standard, mL Absorbancc
10.0 0.0 0.201
10.0 10.0 0.292
10.0 20.0 0.378
10.0 30.0 0.467
10.0 40.0 0.554
(a) Plot the data using a spreadsheet.
(b) Determine an equation for the relationship between absorbance and volume of standard.
(c) Calculate the statistics for the least-squares relationship in (b).
(d) I)ctcrmine the conccnt ration oÍCr in ppm in the sample.
(e) Find the standard deviation of the result in (d).
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Complexometric titrations are generally conducted to determine divalent cations. The most
important applications are the titration of calcium and magnesium with EDTA.
(a)
A supplement tablet containing about 300.00 mg of calcium ion was dissolved, filtered,
and diluted to 100.00 ml volume. Several 2.00 ml samples of the total solution were
titrated with 0.0100 M EDTA solution. The mean corrected titration volume was 13.65
mL. Calculate the calcium content of the supplement tablet in mg units.
(b)
A sample of Epsom Salt of mass 0.7567 g was dissolved uniformly in distilled water in
a 250.00 mL volumetric flask. Portions of the magnesium ion solution of volume 10.00
mL were titrated using a 0.01000 M solution of EDTA. The mean corrected titration
volume was 12.25 ml. Calculate the percentage by mass (% w / w) of the magnesium
in the Epsom Salt sample.
(c)
A 100.00 mL sample of tap water was titrated with 0.0100 M EDTA solution. The mean
corrected titration volume was 14.80 mL. Determine…
The following data were obtained from the spectrophotometric titration of Cu(II) and Ca(II) in an
unknown solution. A 25.00 mL aliquot of the unknown was taken to which 50.0 mL of
ethanolamine buffer and 25.0 mL of distilled water were added. The solution was then titrated
with standard 0.2508 M EDTA solution. Plot the recorded data, absorbance against volume of
EDTA in mL. Correct the absorbance for volume changes. Calculate the number of moles of
Ca(II) and Cu(II) in the unknown sample.
Vol of
Titrant,
mL
Vol of
Titrant,
mL
Abs
Abs
0.0
0.416
12.5
0.886
2.0
0.415
13.0
0.923
4.0
0.409
13.5
0.958
6.0
0.416
14.0
0.979
8.0
0.535
14.5
0.969
10.0
0.690
15.0
0.971
11.0
0.770
15.5
0.964
12.0
0.840
Treatment of ammonia with phenol in the presence of hypochlorite yields indophenol, a blue product that absrobs light at
625 nm, which çan be used for the spectrophotometric determination of ammonia.
gan
OCF
OH + NH3
indophenol anion
To determinè the ammonia concentration in a sample of lake water, three samples are prepared. In sample A, 10.0 mL of lake
water is mixed with 5 mL of phenol solution and 2 mL of sodium hypochlorite solution, and diluted to 25.0 mL in a volumetric
flask. In sample B, 10.0 mL of lake water is mixed with 5 mL of phenol solution, 2 mL of sodium hypochlorite solution, and
2.50 mL of a 5.50 x 10-4 M ammonia solution, and diluted to 25.0 mL. Sample C is a reagent blank. It contains 10.0 mL of
distilled water, 5 mL of phenol solution, and 2 mL of sodium hypochlorite solution, diluted to 25.0 mL. The absorbance of the
three samples is then measured at 625 nm in a 1.00 cm cuvette. The results are shown in the table.
Sample Absorbance (625 nm)
A
0.361
B
0.608
C…
Chapter 9 Solutions
Principles of Instrumental Analysis
Ch. 9 - Prob. 9.1QAPCh. 9 - Prob. 9.2QAPCh. 9 - Why is an electrothermal atomizer more sensitive...Ch. 9 - Prob. 9.4QAPCh. 9 - Prob. 9.5QAPCh. 9 - Prob. 9.6QAPCh. 9 - Prob. 9.7QAPCh. 9 - Prob. 9.8QAPCh. 9 - Prob. 9.9QAPCh. 9 - Prob. 9.10QAP
Ch. 9 - Prob. 9.11QAPCh. 9 - Prob. 9.12QAPCh. 9 - Prob. 9.13QAPCh. 9 - Prob. 9.14QAPCh. 9 - Prob. 9.15QAPCh. 9 - Prob. 9.16QAPCh. 9 - Prob. 9.17QAPCh. 9 - In the concentration range of 1 to 100 g/mL P,...Ch. 9 - Prob. 9.19QAPCh. 9 - Prob. 9.20QAPCh. 9 - Prob. 9.21QAPCh. 9 - The chromium in an aqueous sample was determined...Ch. 9 - Prob. 9.23QAP
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