Chem 113.1 MakeUp Quiz F
Name: __________________________
(Read the questions carefully before answering)
1 [10] A Permanganate stock solution was made by dissolving158 mg Potassium
Permanganate in 150 mL of water. Provide a detailed dilution sequence you would carry
out so an spectrometer will give an absorbance reading between 0.5 and 0.9 (pick any
value between 0.5 and 0.9). At 525 nm the ion MnO4- has an extinction coefficient of
2.24 × 103 cm-1 M-1. Assume you are using a cell with an optical path of 1.00 cm. Use
glassware with volumes you used in the lab to dilute solutions.
158 mg KMnO4 ÷ (158 g/mol) = 1 X 10-3 mol
1 X 10-3 mol K MnO4 ÷ 150 mL = 6.67 X 10-3 mol/L
If A = 0.75  0.75 ÷ ( 2.24 × 103 cm-1 M-1 X 1.00 cm) = 3.35 X 10-4 mol/L
Take the ratio to figure out the dilutions.
6.67 X 10-3 mol/L ÷ 3.35 X 10-4 mol/L = 19.9 ≈ 20
dilute 1:20
dilution (1:10): take 1 mL of the original solution, add 9 mL of water
dilution (1:2): take 1 mL from dilution 1:10, add 1 mL of water to get dilution 1:20
Take dilution 1:20 for measurement in the spectrometer.
3a [6] Balance the following equation in acid solution using the ion electron method.
Cd0 + NO3-
 Cd2+ + NO
Write the two half-reactions:
Cd0  Cd2+ + 2 e4 H+ + NO3- + 3 e-  NO + 2 H2O
Balance atoms (not O and H) and electrons in the half-reactions:
3Cd0  3Cd2+ + 6 e2NO3- + 6 e-  2NO
Balance charges by adding H+ balance H+ by adding H2O:
3 Cd0  3 Cd2+ + 6 e8 H+ + 2 NO3- + 6 e-  2 NO + 4 H2O
Add the two the two half-reactions and cancel anything that is the same on both
sides:
3 Cd0 + 8 H+ + 2 NO3-  3 Cd2+ + 2 NO + 4 H2O
3b [5] Compute the mass (in grams) of Nitric Oxide produced by the oxidation of 225 mg
of Cadmium.
225 mg Cd0 ÷ (112.4 g/mol) = 2 X 10-3 mol
2 X 10-3 mol Cd0 X [ 2 mol NO / 3 molCd0] = 1.33 X 10-3 mol NO
1.33 X 10-3 mol NO X (30.0 g/mol) = 40 mg NO
3c [4] What insoluble product would you get if there was no acid present in the solution.
Explain your reasoning.
Not adding acid will result in the precipitation of the metal oxide: CdO, because there are
no H+ to combine with the O-2.
Chem 113.1 MakeUp Quiz F2
Name: __________________________
(Read the questions carefully before answering)
1 [10] A Permanganate stock solution was made by dissolving 158 mg Potassium
Permanganate in 75 mL of water. Provide a detailed dilution sequence you would carry
out so an spectrometer will give an absorbance reading between 0.5 and 0.9 (pick any
value between 0.5 and 0.9). At 525 nm the ion MnO4- has an extinction coefficient of
2.24 × 103 cm-1 M-1. Assume you are using a cell with an optical path of 1.00 cm. Use
glassware with volumes you used in the lab to dilute solutions.
158 mg KMnO4 ÷ (158 g/mol) = 1 X 10-3 mol
1 X 10-3 mol K MnO4 ÷ 75.0 mL = 13.34 X 10-3 mol/L
If A = 0.75  0.75 ÷ ( 2.24 × 103 cm-1 M-1 X 1.00 cm) = 3.35 X 10-4 mol/L
Take the ratio to figure out the dilutions.
13.34 X 10-3 mol/L ÷ 3.35 X 10-4 mol/L = 39.82 ≈ 40
dilute 1:40
dilution (1:10): take 1 mL of the original solution, add 9 mL of water
dilution 2: take 1 mL from dilution 1:10, add 3 mL of water to get dilution 1:40
Take dilution 1:40 for measurement in the spectrometer.
3a [6] Balance the following equation in acid solution using the ion electron method.
Cd0 + NO3-
 Cd2+ + NO
Write the two half-reactions:
Cd0  Cd2+ + 2 e4 H+ + NO3- + 3 e-  NO + 2 H2O
Balance atoms (not O and H) and electrons in the half-reactions:
3Cd0  3Cd2+ + 6 e2NO3- + 6 e-  2NO
Balance charges by adding H+ balance H+ by adding H2O:
3 Cd0  3 Cd2+ + 6 e8 H+ + 2 NO3- + 6 e-  2 NO + 4 H2O
Add the two the two half-reactions and cancel anything that is the same on both
sides:
3 Cd0 + 8 H+ + 2 NO3-  3 Cd2+ + 2 NO + 4 H2O
3b [5] Compute the mass (in grams) of Nitric Oxide produced by the oxidation of 175 mg
of Cadmium.
175 mg Cd0 ÷ (112.4 g/mol) = 1.56 X 10-3 mol
1.56 X 10-3 mol Cd0 X [ 2 mol NO / 3 molCd0] = 1.04 X 10-3 mol NO
1.04 X 10-3 mol NO X (30.0 g/mol) = 31 mg NO
3c [4] What insoluble product would you get if there was no acid present in the solution.
Explain your reasoning.
Not adding acid will result in the precipitation of the metal oxide: CdO, because there are
no H+ to combine with the O-2.