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(CHEM2310)[2011](s)final~hzhongaa^_67078.pdf
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CHEM 2310 Analytical Chemistry I
Final Examination
Thursday 15 December 2011 Time allowed 3 hrs Total 150pts
Answer all questions on the answer grid provided. You may carry out rough working in the paper provided, but this will not be collected and graded.

Section 1. Multiple Choice (40pts)
1.1 Ionic Strengths (4pts)
What are the ionic strengths of solutions formed from combining solutions of 0.30 M RbNO3 and 0.20 M Na2WO4 in 1:1 and 1:2 ratio respectively ? (answer to 2 sig figs)

a) 0.25 M, 0.23 M b) 0.35 M, 0.37 M c) 0.45 M, 0.50 M d) 0.75 M, 0.70 M
e) 0.90 M, 1.2 M f) None of a-e) correct.
A: c) Sodium tungstate is a 2:1 electrolyte so = 0.60M 1;1 is =(0.3 +0.6) /2 = 0.45M 1:2 is (0.3 +0.6 +0.6)/3 = 0.50M a,b,e,f 1pt
1.2 Electrical Units (4pts)
Which three of the following are incorrect ? (ignore sig figs)
a) 100 W = 500 mA x 2 kV b) 2 A = 2 C / 1 sec
c) 10 C = 1 A x 10 V d) 5 . = 10 V / 2 A
e) 100 V = 50 J x 2 C f) 100 J = 10 W x 10s
A: a) = 1kW c) = 10..e) 100J = 50V x 2C
Subtract 1pt for each missing, -2pts for each incorrectly substituted

1.3 Transmittance and Absorbance (4pts)
Which two statements relating to absorption by an analyte in solution are incorrect ?
a) The transmittance is not inversely proportional to analyte concentration.
(T not . 1/ [analyte])
b) The absorbance is directly proportional to analyte concentration (A . [analyte])
c) If T is approx. 10% for a solution in 1cm path cell, T is approx. 5% for
same solution in 2cm path cell.
d) The relationship of A and T is T = 10-A.
e) An absorbance of 1 corresponds to a transmittance of 0.
f) More than two, or less than two, statements a-e) are incorrect.

A: c) T = 1% for 2cm e) A =1 T = 10%
2pts each -1pt for each incorrectly substituted f 1pt

1.4 Color and Indicators (4pts)

The pH indicator bromo-cresol green is shown below. At pH 3.8 it is yellow with .max at 440nm. At pH 5.4 it is blue. Given a single predominant absorption maximum in the visible region for the blue form, which wavelength 280, 510 or 620 nm is closest to this, and is the form shown below the yellow or blue form of the indicator ?

a) 280 nm, blue b) 510 nm, blue c) 620 nm, blue
d) 280 nm, yellow e) 510 nm, yellow f) 620 nm, yellow


A: f) 620 nm, yellow (acidic) 2pts for c) d) or e) 1pt b

1.5 Standard Reduction Potentials (4pts)
Rank the REDOX equilibria below based on increasingly positive standard reduction
potentials versus S.H.E., (i.e. 2H+ + 2e- H2(g) = 0.000V):


i) Cd2+ + 2e- Cd(s) ii) Al3+ + 3e- Al(s)
iii) Ag+(g) + e- Ag(s) iv) Ce4+ + e- Ce3+
Choose from:
a) i) = -1.677 ii) = -0.402 iii) = +0.799 iv) = +1.720 V
b) iv) = -1.677 i) = -0.402 ii) = +0.799 iii) = +1.720 V
c) ii) = -1.677 iv) = -0.402 iii) = +0.799 i) = +1.720 V
d) ii) = -1.677 i) = -0.402 iv) = +0.799 iii) = +1.720 V
e)