W 460 nm dilution 100 mL c 0.538071 ppm 5 pts 1.2 ...
1.1 The concentration of phenol in a water sample is determined by separating the phenol from nonvolatile impurities by steam distillation, followed by reacting with 4-aminoantipyrine and K3Fe(CN)6 at pH 7.9 to form a colored antipyrine dye. A phenol standard with a concentration of 4.00 ppm has an absorbance of 0.424 at a wavelength of 460 nm using a 1.00-cm cell. A water sample is steam-distilled, and a 50.00-mL aliquot of the distillate is placed in a 100-mL volumetric flask and diluted to volume with distilled water. The absorbance of this solution is found to be 0.394. What is the concentration of phenol (in parts per million) in the water sample?
PhOH std A w b
4 ppm 0.424
460 nm 1 cm
PhOH samp 0.269036 ppm
aliquot
50 mL
dilution
100 mL
A
0.394
c
0.538071 ppm
5 pts
1.2 The determination of phosphate concentration in a washing powder requires first the hydrolysis of the tripolyphosphate components into the phosphate ion or its protonated forms. Then a quantitative colorimetric method based upon the absorption of the yellow complex of phosphate and ammonium vanadomolybdate can be used. A series of standard solutions was prepared. The complex was then developed in 10mL aliquots of these solutions by adding a 5.0mL aliquot of an ammonium vanadomolybdate solution. Measurements were made in a glass cell of 1.0 cm pathlength at 415 nm.
The following absorbance data were obtained.
Solutions C(mmol/L) A
S0
0
0
m
S1
0.1
0.15
b
S2
0.2
0.28
S3
0.3
0.4
S4
0.4
0.55
S5
0.5
0.7
1.377143 0.002381
a.
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0 0
y = 1.3771x + 0.0024 R? = 0.9987
3pts(plot)
0.1
0.2
0.3
0.4
0.5
0.6
b. By the method of least squares, derive an equation relating absorbance to phosphate concentration.
A=1.3771c+0.0024
2pts(equation)
c. An unknown solution obtained by hydrolysis of 1 g of detergent treated in an identical way gave an A50 absorbance of 0.45. Determine the phosphate concentration of this solution.
1g
A
0.45
c
0.325035 mmol/L
3pts
2.1 To determine the concentrations (mol/L) of Co(NO3)2 (A) and Cr(NO3)3 (B) in an unknown sample, the following representative absorbance data were obtained
A (mol/L) B (mol/L) 510nm 575nm
0.15
0
0.714 0.097
0
0.06
0.298
0.757
Unknown Unknown 0.671
0.33
points given if solution is clearly presented
A
Abs
e
b
C
510 0.714
4.76
1
0.15
1pt
575 0.097 0.646667
1
0.15
1pt
B
510 0.298 4.966667
1
0.06
1pt
575 0.757 12.61667
1
0.06
1pt
2 equations, 2 unknown
at 510nm
0.671 =
4.76 bCA
+
4.966667 bCB
at 575nm
0.33 =
0.646667 bCA
+
12.61667 bCB
solve for CA by eliminating CB (also note b=1)
1.70452 =
12.09168 bCA
+
-
0.33 =
0.646667 bCA
+
1.37452 =
11.44501 CA
12.61667 bCB 12.61667 bCB
0
CA
0.120098 mol/L
1pt
substitute CA in one of the above equations to get CB
CB
0.02 mol/L
1pt
3.1
A100
63
96.4 ppm
a
b sample y
x
390
0.9
0.33
0.65 0.722222 0.366667
430
0.88
0.5
0.74 0.840909 0.568182
450
0.69
0.53
0.67 0.971014 0.768116
470
0.48
0.51
0.55 1.145833 1.0625
slope and intercept is clearly identified (or in equation form)
slope
0.611921
2pts
y-int
0.496934
2pts
points given if solution is clearly presented
Cb
58.98915 ppm
=E106*D99
1pt
Ca
31.30682 ppm
=E107*C99
1pt
3.2 Blanco and co-workers reported several examples of the application of multiwavelength linear regression analysis for the simultaneous determination of mixtures containing two components with overlapping spectra. For each of the following, determine the molar concentration of each analyte in the mixture.
a. A mixture of MnO4? and Cr2O72?, and standards of 1.0 x 10?4 M KMnO4 and 1.0 x 10?4 M K2Cr2O7 gave the following results
wl(nm) 266 288 320 350 360
M std C std
1.00E-04 1.00E-04
0.042
0.41
0.082 0.283
0.168 0.158
0.125 0.318
0.056 0.181
slope y-int
Cr2O72MnO4?
Mixture
y
x
0.766 18.2381 9.761905
0.571 6.963415 3.45122
0.422 2.511905 0.940476
0.672 5.376 2.544
0.366 6.535714 3.232143
slope and intercept is clearly identified (or in equation form)
1.78386
2pts
0.814653
2pts
points given if solution is clearly presented
1.78E-04 M
=E131*D124
1pt
8.15E-05 M
=E132*C124
1pt
b. Titanium and vanadium were determined by forming the H2O2 complexes. Results for a mixture of Ti(IV) and V(V) and standards of 63.1 ppm Ti(IV) and 96.4 ppm V(V) are listed in the following table Absorbances
Ti(std) V(std)
w(nm)
63.1
96.4 Mixture
y
x
390 0.895 0.326 0.651 0.727374 0.364246
430 0.884 0.497 0.743 0.840498 0.562217
450 0.694 0.528 0.665 0.958213 0.760807
470 0.481 0.512 0.547 1.137214 1.064449
510 0.173 0.374 0.314 1.815029 2.16185
slope and intercept is clearly identified (or in equation form)
slope
0.606898
2pts
y-int
0.499258
2pts
points given if solution is clearly presented
[V]
58.505 ppm
=E150*D143
1pt
[Ti]
31.5032 ppm
=E151*C143
1pt
c. Copper and zinc were determined by forming colored complexes with 2-pyridyl-azo-resorcinol (PAR). The absorbances for PAR, a mixture of Cu2+ and Zn2+, and standards of 1.0-ppm Cu2+ and 1.0-ppm Zn2+ are listed in the following table. Note that you must correct the absorbances for the metal for the absorbance due to the PAR.
Absorbances
w(nm) PAR
Cu std Zn std Mixture
480 0.211 0.698 0.971 0.656
496 0.137 0.732 1.018 0.668
510
0.1 0.732 0.891 0.627
526 0.072 0.602 0.672 0.498
540 0.056 0.387 0.306
0.29
corrected Absorbances
Cu std Zn std Mixture
w(nm)
1
1
y
x
480 0.487
0.76 0.445 0.913758 1.560575
496 0.595 0.881 0.531 0.892437 1.480672
510 0.632 0.791 0.527 0.833861 1.251582
526
0.53
0.6 0.426 0.803774 1.132075
540 0.331
0.25 0.234 0.706949 0.755287
slope and intercept is clearly identified (or in equation form)
slope
0.256297
2pts
y-int
0.513363
2pts
points given if solution is clearly presented
Zn
0.256297 ppm
=E178*D171
1pt
Cu
0.513363 ppm
=E179*C171
1pt
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