1.12: Electrochemical Measurements

1. The antibiotic Valinomycin has a high affinity for:
   1. sodium
   2. lithium
   3. potassium
   4. calcium
   5. magnesium
2. In the Nernst equation, E⁰ represents:
   1. measured volume
   2. gas constant
   3. electrons transferred
   4. Faraday constant
   5. standard half cell potential

Match the items in Column B with the definitions in Column A for questions 3-7:

B voltometry of a dropping Hg electrode the measurement of current passing through a solution at a given charge measurement of charge measurement of current at a constant potential measurement of current as a function of potential

A amperometry coulometry conductometry polarography voltammetry

8. The K ion electrode has an absolute specificity for K and therefore has interferences from no other cations.
   1. true
   2. false
9. The PCO₂ electrode reduces O₂ to H₂O and measures the resulting decrease in current
   1. true
   2. false
10. The statement which most correctly describes the measurement of pH with a glass electrode is:
    1. hydrogen ions pass through a special kind of permeable glass
    2. the internal and external half-cells have the same potential
    3. a special kind of glass sensitive to hydrogen ions is used
    4. the temperature knob on the pH meter compensates for the influence of temperature
    5. temperature is not involved with pH measurements
11. In potentiometric measurements, the voltage difference between the indicator and reference electrodes is proportional to:
    1. ion concentration (mmol/L)
    2. ion activity
    3. log of ion concentratioin (mmol/L)
    4. log of ion activity
    5. ion concentration (mg/L)
12. In the PCO₂ electrode, all of the following are true except:
    1. carbon dioxide from the sample chamber diffuses through a membrane and dissolves in electrolyte solution
    2. the PCO₂ electrode measures pH change caused by the production of carbonic acid
    3. the measuring electrode is a CO₂ specific electrode
    4. the measuring and reference electrodes are combined into one unit
    5. the CO₂ measurement can be related to total CO₂

Use the following Key to answer Questions 13 - 19:

1. 1, 2, and 3 are correct
2. 1 and 3 are correct
3. 2 and 4 are correct
4. only 4 is correct
5. all are correct

13. The CO₂ electrode works by:
    1. measuring a potentiometric change
    2. measuring a change in current
    3. measuring a change in pH
    4. using an enzymatic reaction with CO₂
14. Ion selective electrodes:
    1. allow ion exchange on surface resulting in a change of potential
    2. are pH dependent
    3. are temperature dependent
    4. do not require a reference electrode
15. Potentiometry:
    1. is the measurement of the electrical potential difference between two electrodes in an electrochemical cell
    2. measures voltage
    3. applications include pH and PCO₂ measurements
    4. principles are used for measuring potassium using valinomycin membrane
16. Which of the following devices are considered to be of the amperometric—coulometric type?
    1. PO₂ electrode
    2. pH electrode
    3. Chloridometer (Cotlove)
    4. PCO₂ electrode
17. A KCl salt bridge, widely utilized in electrochemical cells, has all of the following functions except:
    1. lowers liquid—junction potentials
    2. conducts electricity
    3. allows ions to migrate
    4. measures the potential between two solutions
18. The PCO₂ electrode of a blood gas instrument measures:
    1. reduction of CO₂ at the cathode
    2. change in pH of the electrode solution
    3. the time required for CO₂ to pass through a special membrane
    4. partial pressure of CO₂
19. Which statement(s) is/are false concerning the chloridometer?
    1. generating anode generates silver ions
    2. electrons from the generating electrodes combine with hydrogen ions to form hydrogen gas
    3. automatic timer is initiated at the start of the silver ion generation
    4. AgCl is sensed by the detector electrode

Answer

1. c (p. 277)
2. e (p. 274)
3. d (p. 282)
4. c (p. 285)
5. b (p. 283)
6. a (p. 282)
7. a (p. 282)
8. b (p. 277,280)
9. b (p. 279-282)
10. c (p. 278-279)
11. d (p. 274,276)
12. c (p. 279)
13. b (p. 279)
14. a (p. 276-277)
15. e (p. 273-274)
16. b (p. 282-285)
17. d (p. 273)
18. c(p. 279)
19. c (p. 285)