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- (10 points) What is the cell potential for the galvanic cell described by the line notation below?
Mg(s) | Mg(OH)+ (45.92 mM), pH = 6.05 || IrCl62– (15.47 mM), Cl– (9.02 mM) | Ir(s)
- (5 points) Write out the Beer’s law equation and identify all the variables.
𝞮 = molar absorptivity (1/M•cm)
- = path length (cm)
- = molar concentration (M)
- (5 points) For the following questions consider the three principle types of spectrometers that are used for analyses: flame, graphite furnace, and inductively coupled plasma (ICP). For each question select the best system:
- Which instrument is capable of analyzing solids?
- Which instrument reaches the highest temperatures?
- Which instrument has the longest path length?
- Which is best for atomic emission spectroscopy?
- Which can execute a programed temperature cycle?
- (10 points) A tin (Sn) metal indicator electrode is being used to determine the concentration of sulfide (S2–) in an unknown solution. The measurement is done by mixing a known tin nitrate (Sn(NO3)2) solution with some of the sulfide solution (details below) and measuring the potential of the solution with a tin electrode, and a SCE reference electrode (0.241 V).
The mixture was made by combining 20.00 mL of 30.12 mM Sn(NO3)2 and 50.00 mL of the unknown sulfide solution. The Ksp for tin sulfide is 1.3×10–26.
The cell potential was measured to be –1.080 V. What is the concentration of S2– in the unknown solution?
- (10 points) You are measuring the amount of iron via a colorimetric reaction with 1,10phenanthroline. You can quantify the amount of iron by the absorbance that you can measure form the metal-dye complex.
You have added an excess of the 1,10-phenanthroline to a solution containing an unknown amount of iron. When the absorbance is measured you obtain a value of
You then mix 15.00 mL of that unknown solution with 30.00 mL of an iron standard solution that contains 73.23 µM iron and an excess of the 1,10-phenanthroline. When you measure the absorbance of this solution you get an absorbance value of 0.682 AU.
What is the concentration of iron in the unknown solution?
- (10 points) A liquid chromatographic (LC) instrument is being used to quantify the calcium content of a soy milk. To test the detector for the LC a standard solution containing 515 ppm Ca2+ and 145 ppm Cd2+ is measured, and the peak areas for the two metals are found to be 1531 and 583 respectively.
A 20.00 mL sample of the soy milk is mixed with 5.00 mL of the cadmium internal standard (225 ppm). When the peak areas are obtained for calcium and cadmium they are found to be 1450 and 181 respectively.
What is the ppm concentration of calcium in the soy milk?
Note: keep all concentrations in ppm throughout this problem for simplicity.
E =K+ 0.05916 log([A]+KA,I [I]zzAI ) KA,I = [Az]zAI
CA %VA (+Cspike %’Vspike (*
CA ‘ * &VT ) & VT )
%VO ( C %V ( %V (
CA ‘ * A ‘ O *+Cspike ‘ spike *
&VF ) &VF )
SA kACA K×CIS
SIS kISCIS CA
−b± b2 −4ac
& VF )
K = ×
Selected Standard Reduction Potentials
Mg(OH)+ + H+ + 2e– ⇌ Mg(s) + H2O
Mg(OH)2(s) + 2e– ⇌ Mg(s) + 2OH–
IrCl62– + e– ⇌ IrCl63–
IrCl62– + 4e– ⇌ Ir(s) + 6Cl–
Sn4+ + 2e– ⇌ Sn2+
Sn2+ + 2e– ⇌ Sn(s)