REFINEMENT OF THE SECOND VERSION OF THE TWO TIER MULTIPLE-CHOICE DIAGNOSTIC INSTRUMENT

The second version of the two-tier multiple-choice diagnostic instrument (Appendix G2) was sent to one senior chemistry teacher and two chemistry lecturers for further comments and improvement to the instrument. Most of the responses were maintained except for minor changes to items 1, 2, 3, 6, 7, 9, 10, 11, 12, 16 and 17. Of the total 18 items, only Item 18 was deleted. This resulted in the final version of two-tier electrolysis diagnostic instrument (EDI) with 17 items which can be found in Appendix H.

Item 1

The formula CCl4 was added to tetrachloromethane in reasons (1) and (2), and HCl was added to hydrochloric acid in reason (3) because students may be more familiar with the formula than the name of the compound.

Item 2

All the four reasons were rephrased to

(1) Positive ions move to X and accept electrons. (2) Negative ions move to X and donate electrons. (3) Positive ions move to Y and donate electrons. (4) Negative ions move to Y and accept electrons.

This was to test the students on the movement of ions and what happens at the anode with respect to electrons.

Item 3

‘Positively charged magnesium ions’ in all the four responses were changed to ‘Magnesium ions’, without giving any clue to the type of charged ions of magnesium, thus students have to know the correct type of charge. The phrase ‘give up electrons’ in reason (2) and (3) were replaced with ‘donate electrons’ to be consistent with what the students have been taught.

Item 6

In reason (1), the phrase ‘SO42- and H+ ions’ was replaced with ‘Sulphate and hydrogen ions’ to avoid confusion with the formula of ions. Similarly, in reason (2), ‘SO42- and OH- ions’ was replaced with ‘Sulphate and hydroxide ions’, and in reason (4), ‘H+ and OH- ions’ was replaced with ‘Hydrogen and hydroxide ions’. Reason (5) ‘No reaction occurs because platinum electrodes are inert’ was added.

Item 7

The formula of the ions in reasons (2), (3), and (4) were all replaced with words. H+ in reason (2) was replaced with ‘hydrogen ions’, H+ and OH- in reasons (3) and (4) were replaced with ‘hydrogen and hydroxide ions’.

Item 9

In reason (1) and (2), ‘Cu2+ ions’ was replaced with ‘Copper(II) ions, whereas in reason (3) and (4), ‘Cl- ions’ was replaced with ‘Chloride ions’. The phrase ‘give up electrons’ in reason (2) and (4) was changed to ‘donate electrons’ to be consistent with what the students are being taught in schools.

Item 10

In reason (1), H+, OH-, Zn2+ and NO3- ions are replaced with the words ‘hydrogen, hydroxide, zinc and nitrate ions’ respectively to be more consistent with the all the other reasons.

Items 11 and 12 help to evaluate understanding of the similar principles involved in electroplating and metal purification by electrolysis.

Item 11

The phrase ‘a metal spoon’ in the stem of item 10 was replaced with ‘an iron spoon’ in order to be more specific on the type of spoon used. In reason (1) and (2), ‘Ag+ ions’ was replaced with ‘Silver ions’, whereas in reason (3) and (4), the phrase ‘H+ present in water’ was replaced with ‘Hydrogen ions’ because ‘water’ might confuse the students.

Item 12

The phrase ‘Cu2+ ions’ in reason (1) and (2) was replaced with ‘Copper(II) ions’ and became reason (3) and (4) respectively in the final version. In reason (3) and (4), the phrase ‘H+ ions present in water’ was replaced with ‘Hydrogen ions’ and became reason (1) and (2) respectively in the final version.

Item 15

Reason (1) was replaced with ‘Gases such as hydrogen and oxygen are released into the atmosphere’. Reason (3) was changed to become reason (2) in the final version as it is a shorter statement. In reason (2) of the draft, the phrase ‘chemical wastes such as cadmium and nickel ions’ is replaced with ‘heavy metal ions such as cadmium and nickel’ to emphasise the nature of the ions, and this became reason (3) in the final version.

Item 16

The stem of item 16 was further improved to ‘In the motor industry, the metals nickel and chromium are used for electroplating’ to give a clearer idea. Reason (1) was changed to ‘The metals are chemically unreactive’ and became reason (4) in the final version; reason (2) was simplified to ‘The metals prevent rusting’ and became reason (3) in the final version; reason (3) was rearranged as reason (2) in the final version; and reason (4) was rearranged as reason (1) in the final version.

Item 17

The stem was changed to ‘Cutlery items are often electroplated with silver and nickel’, and reasons (1), (2), (3) and (4) were changed to

(1) Nickel reacts readily with silver. (2) Silver and nickel are expensive metals. (3) The cutlery becomes more brittle.

(4) The cutlery becomes more resistant to corrosion.

Item 18 was deleted because all the reasons can be possible answers. This led to the final version with 17 items, a copy of which can be found in Appendix H. A table of specifications for the 17 items final version of the electrolysis diagnostic instrument (EDI) is shown in Table 6.10.

Table 6.10 Table of specifications for the 17 items final version of the electrolysis diagnostic instrument (EDI)

Item No.

Concepts Tested Propositional Knowledge Statements

Possible Alternative Conceptions

1 Electrolyte and non- electrolyte

1, 2, 3 Tetrachloromethane contains more ions; Tetrachloromethane consists of free moving ions; The carbon anode dissolves producing ions. 2 Electrodes: Anode and

cathode

7, 10, 13, 15, 16 Positive ions move to the anode and accept electrons; Positive ions move to the cathode and donate electrons; Negative ions move to the cathode and accept electrons.

3 Electrolysis of molten magnesium oxide

13, 15, 16, 17 Magnesium ions are attracted to the anode and accept electrons; Magnesium ions are attracted to the cathode and donate electrons; Magnesium ions are attracted to the anode and donate electrons.

4 Electrolysis of molten lead(II) bromide

13, 15, 16, 18, 19 Bromide ions move to the cathode and are oxidised; Lead(II) ions are positively charged and so move to the anode; Oxygen is attracted to the anode. 5 Electrolysis of aqueous

iron(II) sulphate using platinum electrodes

21, 22, 23, 24, 25 Neither iron(II) ions nor sulphate ions are discharged, so the concentration of the solution remains unchanged; Hydrogen ions and hydroxide ions are discharged, so the concentration of the solution remains unchanged; The concentration of iron(II) ions decreases as iron is deposited at the cathode.

Item No.

Concepts Tested Propositional Knowledge Statements

Possible Alternative Conceptions

6 Products of electrolysis of dilute sulphuric acid using inert electrodes

22, 23, 24, 25, 26 Sulphate and hydrogen ions are selectively discharged; Sulphate and hydroxide ions are selectively

discharged; The electrolyte consists of hydrogen ions and oxygen ions; No reaction occurs because platinum electrodes are inert.

7 Change to the concentration of electrolyte during electrolysis of dilute sulphuric acid using inert electrodes

25, 26, 27 Hydrogen and oxygen ions are selectively discharged, so the concentration of the acid decreases; Hydrogen and sulphate ions are selectively discharged, so the concentration of the acid decreases; Hydrogen and hydroxide ions are selectively discharged, so the concentration of the acid remains the same.

8 Electrolysis of aqueous copper(II) sulphate using platinum electrodes

28, 29, 30, 32 Copper(II) ions are displaced by platinum, so the colour of the electrolyte decreases in intensity; Platinum

dissolves in the electrolyte, so the colour of the electrolyte increases in intensity; Platinum electrodes are inert, so the colour of the electrolyte remains the same.

9 Electrolysis of

concentrated aqueous solution of copper(II) chloride using graphite electrodes

7, 19, 23, 24, 25 Copper(II) ions move to the anode and accept electrons; Copper(II) ions move to the anode and donate electrons; Chloride ions move to the anode and accept electrons.

10 Electrolysis of aqueous zinc nitrate using graphite electrodes

23, 24, 25 Hydrogen ions are discharged at the cathode, producing hydrogen gas; Reaction occurs between zinc ions and the graphite electrodes; Zinc is deposited at the cathode. 11 Electroplating an iron

spoon

12, 37, 39 Silver ions are attracted to the anode and selectively discharged; Hydrogen ions are attracted to the cathode and selectively discharged; Hydrogen ions are attracted to the anode and selectively discharged.

12 Purifying an impure copper plate

12, 22, 23, 24, 36 Hydrogen ions are attracted to the cathode and selectively discharged; Hydrogen ions are attracted to the anode and selectively discharged; Copper(II) ions are attracted to the anode and selectively discharged.

13 Manufacture of chlorine 22, 23, 24 Hydrogen ions are preferably

discharged over hydroxide ions; Aqueous sodium chloride does not contain hydrogen ions; The

concentration of hydrogen ions is very low.

Item No.

Concepts Tested Propositional Knowledge Statements

Possible Alternative Conceptions

14 Extraction of aluminium metal from molten

aluminium oxide using graphite electrodes

10, 15, 16, 35 The anode dissolves in the hot molten aluminium oxide; The cathode dissolves in the hot molten aluminium oxide; The oxygen produced at high temperatures oxidises the cathode.

15 Effect on the environment by the use of electrolysis in industry

41 Gases such as hydrogen and oxygen are

released into the atmosphere; Chemical wastes are released into the environment after proper treatment.

16 Electroplating in the motor industry

38 The metals have high boiling and melting points; The metals do not form a strongly adhering coating; The metals are chemically unreactive.

17 Electroplating on cutlery items

38 Nickel reacts readily with silver; Silver and nickel are expensive metals; The cutlery becomes more brittle.

SUMMARY

Students who showed alternative conceptions in their answers to the free response instrument in Study 2 were interviewed to gain further insight into their reasons chosen. The interview was conducted in Interview Two in Study 3. The first version of the two-tier multiple-choice instrument which consisted of 21 items after a review by three senior chemistry teachers and two chemistry lecturers was reduced to 18 items. Changes made to the items were discussed. A further review in Study 4 by one senior chemistry teacher and two chemistry lecturers subsequently produced the 17 items in the final two-tier multiple-choice electrolysis diagnostic instrument (EDI). A copy of the electrolysis diagnostic instrument (EDI) is found in Appendix H. This instrument was used in the main study with 330 Form Four chemistry students in Kuching, Malaysia in October and November, 2007 and this will be discussed in the next chapter.