3B Scientific Electrochemistry Kit - Manual (Page 18)

19
Experiment 6 - Measuring voltage Student instructions
Measuring the standard electrochemical potentials of various non-metals
Chemicals Hazard
symbols
R phrases S phrases Equipment
Meter
Sodium chloride --- --- Electrodes:
2 C, 1 Pt gauze
Potassium bromide --- --- 2 Experiment cables
Sodium iodide --- --- 1 Mains power supply
Hydrochloric acid 1 mol/l 36/37/38 26 2 Pipettes
Distilled water --- --- 1 3V adapter
Warning: Please take care: Hydrochloric acid is corrosive!
Experiment procedure:
1. The prepared 1.0 molar electrolyte solutions should be given to the students. Students require no more
than 10 ml of the relevant solution each.
2. Assemble the battery block as described.
3. Add the 1 molar hydrochloric acid to one chamber of the battery block using the pipette and insert the
platinum gauze electrode into this cell.
4. Add a 1 molar NaCl solution to a second chamber (opposite the platinum gauze electrode) and insert a
carbon electrode.
5. To form a normalized hydrogen electrode, a 3V adapter is connected to the power supply. Connect the
negative pole of the 3V adapter to the platinum gauze electrode and the positive pole to the carbon
electrode using experiment cables. Connect the power supply to the 230 V mains and electrolyze the
platinum gauze for about 30 seconds. Hydrogen forms at the platinum gauze and completely surrounds
the gauze.
6. The 3V adapter is then replaced by the meter and the Cl
-
/ Cl
2
voltage can then be read off.
7. Proceed as in steps 4 to 6 with each of the other non metals dipping the carbon electrode into potassium
bromide and potassium iodide one after the other to determine the electrochemical potentials of Br - / Br
2
and I
-
/ I
2
.
Observation and evaluation:
Sketch of experiment set-up:
Result of voltage measurement:
Cl
-
/ Cl
2
V
Br
-
/ Br
2
V
I
-
/ I
2
V