Zadanie 1c, Paper 2, maj 2025, TZ1: Chemia IB SL

Zadania w arkuszu

Informacja do zadań 1a-1c.

Heating a mixture of powdered tin and iodine gives the compound tin(IV) iodide, $\ce{SnI4}$

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A student proposed that, because tin(IV) iodide might be ionic, electrolysing the molten compound with inert electrodes should regenerate tin and iodine.

(i) Label the diagram of the electrolytic cell to show which electrode is the anode and which is the cathode, and mark the direction in which each type of ion moves through the melt.

electrolytic cell with a d.c. power supply above the cell (positive terminal on the left wire, negative terminal on the right wire), two electrodes dipping into molten tin(IV) iodide containing Sn4+ and I- ions, and an empty label box beside each electrode

(ii) Write a half-equation for the electrode process taking place at each of the two electrodes.

Negative electrode:

Positive electrode:

(iii) Contrast one physical property of tin and tin(IV) iodide.

Sprawdzane umiejętności

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Odpowiedź z klucza

(i) left electrode: anode AND right electrode: cathode ✔

$\ce{I-}$ ions move to the left electrode «the anode» AND $\ce{Sn^4+}$ ions move to the right electrode «the cathode» ✔

(ii) Negative electrode «cathode»: $\ce{Sn^4+ + 4e- -> Sn}$

Positive electrode «anode»: $\ce{2I- -> I2 + 2e-}$

(iii) Any one of:

tin conducts electricity / heat AND tin(IV) iodide does not ✔

OR

tin is malleable / ductile AND tin(IV) iodide is brittle ✔

OR

tin has a metallic lustre / is silvery AND tin(IV) iodide is an orange crystalline solid with no metallic lustre ✔

OR

tin has a higher melting point «232 °C» than tin(IV) iodide «144 °C» ✔

OR

tin is denser than tin(IV) iodide ✔

Schemat punktowania

(i) Do not apply ECF. Award [1] if any two of the four elements (two electrode names, two ion directions) are correct, and [2] when all four are correct. (ii) Award [1 max] for correct equations written at the wrong electrodes. Do not accept reverse equations. Penalize equilibrium arrows once only. (iii) [1] for any one correct contrast that states the property for both substances; do not accept chemical properties or molar mass.

Komentarz

The student's proposal only sets up the exercise: nothing here asks whether tin(IV) iodide is really ionic, only that the electrolysis of the molten salt be worked through as if it gave simple ions.

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