C317PracticeExam2Spring2008

C317PracticeExam2Spring2008 - CHEMISTRY C317 EQUILIBRIA AND...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
CHEMISTRY C317: EQUILIBRIA AND ELECTROCHEMISTRY Spring, 2008 Practice Examination 2 1. Suppose that you wish to attempt the separation of Cu 2+ from SbO + by controlled-potential deposition of copper metal onto a platinum cathode. Assume that the original sample solution contains 1.00 M H + , 0.0350 M Cu 2+ , and 0.500 M SbO + , and that [H + ] remains at 1.00 M throughout the course of the electrolysis. Cu 2+ + 2 e Cu ; E º = +0.337 V vs. SHE SbO + + 2 H + + 3 e Sb + H 2 O ; E º = +0.212 V vs. SHE (a) At what potential (versus SHE) must the platinum cathode be controlled to cause 99.9% deposition of elemental copper? (b) What fraction of the SbO + will be reduced to the elemental (Sb) state under the experimental conditions imposed in part (a)? (c) If the volume of the original sample solution is 100.0 mL, what will be the total weight gain ( in milligrams ) of the platinum cathode under the experimental conditions imposed in part (a)? [Atomic masses: Cu = 63.55; Sb = 121.76] 2. An unknown Cd 2+ solution was analyzed by means of polarography. A 30.00-mL sample of the unknown solution was found to yield an average diffusion current, ( i d ) average , of 2.06 µA. Next, a 4.00-mL aliquot of a standard 2.59 × 10 –3 M Cd 2+ solution was added to the 30.00-mL unknown sample, and the resulting mixture gave an average diffusion current, ( i d ) average , of 5.41 µA. Calculate the molar concentration of Cd 2+ in the original unknown solution. 3. For a cyclic voltammetry experiment, one can use the Randles-Sevčik equation i p = (2.67 × 10 5 ) n 3/2 D 1/2 v 1/2 A C to calculate the peak current ( i p ) in amperes, as a function of the number of electrons transferred ( n ), the diffusion coefficient ( D ) in cm 2 /sec, the scan rate ( v ) in volts/sec, the area of the electrode ( A ) in cm 2 , and the concentration ( C ) in mol/cm 3 . In a certain set of experiments, the reversible two-electron oxidation of o -dianisidine was explored. NH 2 H 2 N OCH 3 H 3 CO o -dianisidine (a) When a carbon electrode with an area of 0.0273 cm 2 was used to study the two-electron oxidation of a 2.27 × 10 –3 M solution of o -dianisidine at a scan rate of 0.500 volt/sec, the peak current was found to be 8.19 µA. Calculate the diffusion coefficient ( D ) for o -dianisidine. (b) If the carbon electrode used in part (a) was employed to investigate the cyclic voltammetric behavior of a 8.20 × 10 –3 M solution of o -dianisidine, what peak current ( i p ) would be expected for a scan rate of 0.100 volt/sec? (c) Suppose that a solution containing an unknown concentration of o -dianisidine was analyzed by means of cyclic voltammetry. For a carbon electrode with an area of 0.0775 cm 2 , the observed peak current ( i p ) was 21.9 µA at a scan rate of 0.200 volt/sec. Calculate the molar concentration of o -anisidine?
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
4. A mixture of Ni 2+ and Co 2+ was analyzed by means of controlled-potential electrolysis. Exactly 10.00 mL of the Ni 2+ –Co 2+ mixture was pipetted into an electrolysis cell containing an electrolyte solution. Quantitative reduction
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 7

C317PracticeExam2Spring2008 - CHEMISTRY C317 EQUILIBRIA AND...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online