The item analysis of the 17 items that was reported in the preceding section has revealed that 29 alternative conceptions were held by the Form 4 students to whom the instrument was administered. These alternative conceptions were identified using the criteria that 10% or more of the students had chosen the answer as shown in Table 7.3. These 29 alternative conceptions, which relate to the students’ ability to explain electrolysis are summarised in Table 7.8. Some of the alternative conceptions were revealed in more than one item. These repeating alternative conceptions are listed only the first time they have been identified. No alternative conceptions were evident from Item 1.
Table 7.8 Alternative conceptions held by students (n = 330) about items in electrolysis diagnostic instrument
Electrolysis Reactions
Item No.
Choice Alternative Conceptions
Electrolyte and non- electrolyte 1 None Electrodes: Anode and cathode 2 B A1 A3
AC1: The terminal connected to the positive terminal of the battery is the cathode. (14%)
AC2: During electrolysis the cations migrate to the anode. (11%)
AC3: Cations (positive ions) possess an excess of electrons. (14%)
Electrolysis of molten magnesium oxide using carbon electrodes
3 B2 AC4: During electrolysis of molten magnesium oxide using inert electrodes magnesium ions are attracted to the cathode where excess electrons on the cations are given up. (18%)
Electrolysis of molten lead(II) bromide using graphite electrodes
4 A1 AC5: During electrolysis of molten lead(II) bromide using inert electrodes bromide ions are oxidised at the cathode. (15%) Electrolysis of dilute aqueous iron(II) sulphate solution using platinum electrodes 5 A4 B1 B2
AC6: During electrolysis of dilute aqueous iron(II) sulphate solution using inert electrodes iron(II) ions are selectively discharged over hydrogen ions. (23%)
Non C: During electrolysis of dilute aqueous iron(II) sulphate solution using inert electrodes neither iron(II) ions nor sulphate ions are discharged. (21%)
AC7: During electrolysis of dilute aqueous iron(II) sulphate solution using inert electrodes the concentration of the solution remains unchanged. (13%)
Electrolysis of dilute sulphuric acid using inert electrodes
6 A3
B4
AC8: During electrolysis of dilute sulphuric acid using inert electrodes, oxygen is produced at the anode as a result of the discharge of oxygen ions. (10%)
AC9: During electrolysis of dilute sulphuric acid using inert electrodes, the products are oxygen at the cathode and hydrogen at the anode. (10%)
Electrolysis Reactions
Item No.
Choice Alternative Conceptions
7 B1
B2
B4
AC10: During electrolysis of dilute sulphuric acid using inert electrodes, the concentration of the solution decreases because hydrogen and oxygen ions are selectively discharged. (11%)
AC11: During electrolysis of dilute sulphuric acid using inert electrodes, the concentration of the solution decreases because hydrogen and sulphate ions are selectively discharged. (14%)
AC12: During electrolysis of dilute sulphuric acid using inert electrodes, the concentration of the solution remains unchanged. (20%) Electrolysis of aqueous copper(II) sulphate using platinum electrodes 8 A4 B2
AC13: During electrolysis of aqueous copper (II) sulphate using platinum electrodes, platinum does not take part in the reaction. (13%)
AC14: During electrolysis of aqueous copper(II) sulphate using platinum electrodes, copper ions are displaced by platinum. (10%) Electrolysis of concentrated aqueous solution of copper(II) chloride using graphite electrodes 9 A1& A2 A3
AC15: During electrolysis of concentrated aqueous solution of copper(II) chloride using graphite electrodes, cations migrate to the anode. (22%)
AC16: During electrolysis of concentrated aqueous solution of copper(II) chloride using graphite electrodes, anions migrate to the anode and accept electrons. (19%) Electrolysis of dilute
aqueous zinc nitrate solution using graphite electrodes
10 A2 & B2
B4
Non C: When dilute aqueous zinc nitrate solution is electrolysed using graphite electrodes, the only gas given off is hydrogen at the cathode. (11%)
AC17: When dilute aqueous zinc nitrate solution is electrolysed using graphite electrodes, zinc is deposited at the cathode. (11%)
Electroplating an iron spoon
11 A
A1
AC18: In electroplating an iron spoon with silver the spoon should be used as the anode. (39%)
AC19: In electroplating an iron spoon with silver using aqueous silver nitrate solution as electrolyte, the silver ions (cations) migrate to the anode. (13%)
Electrolysis Reactions
Item No.
Choice Alternative Conceptions
Purifying an impure copper plate
12 B3 AC20: In purifying an impure copper plate using aqueous copper sulphate solution, the copper(II) ions migrate to the anode. (11%) Manufacture of chlorine 13 A1 B3 B4
AC21: In the manufacture of chlorine by electrolysis of concentrated aqueous sodium chloride solution using graphite electrodes, hydrogen gas is produced because hydrogen ions are preferably discharged over hydroxide ions. (10%)
AC22: In the manufacture of chlorine by electrolysis of concentrated aqueous sodium chloride solution using graphite electrodes, hydrogen gas is not produced because no hydrogen ions are present. (14%)
AC23: In the manufacture of chlorine by electrolysis of concentrated aqueous sodium chloride solution using graphite electrodes, hydrogen gas is not produced because the concentration of hydrogen ions is very low. (13%) Extraction of aluminium metal from aluminium oxide 14 A1 B1& B2
AC24: In the electrolysis of molten aluminium oxide using graphite electrodes, the anode dissolves in the hot aluminium oxide. (16%)
AC25: In the electrolysis of molten aluminium oxide using graphite electrodes, the graphite anode does not have to be periodically replaced. (21%) Effect on the environment by the use of electrolysis in industry 15 A2 B
AC26: Chemical wastes are released into the environment after proper treatment. (18%)
AC27: The use of electrolysis in industry does not cause pollution of the environment. (32%)
Electroplating in the motor industry
16 B2 AC28: In the motor industry, the metals nickel and
chromium are not used for electroplating because the metals do not form a strongly adhering coating. (12%) Electroplating on
cutlery items
17 A1 AC29: Cutlery items are often electroplated with silver and nickel because nickel reacts readily with silver. (10%) Note: The percentage of students displaying each alternative conception (AC) or non conception (Non C) is indicated in parenthesis)