potassium iodide solution using carbon electrodes

Question

1.when potassium iodide solution is electrolysed using carbon electrodes, which pair of products will be produced?

A.potassium,oxygen

B.potassium,iodine

C.hydrogen,oxygen

D.hydrogen,iodine

ANS + Explanations

thx!!!

咁如果題目冇俾~咁當佢係dil定conc?

Answer 1

The answer is D.

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Reason :
In the solution, potassium iodide give K+(aq) ion and I-(aq) ion, and water is slightly ionized to give H+(aq) ion and OH-(aq) ion.

Anode : I-(aq) and OH-(aq) ions migrate to the anode. Since I-(aq) is more concentrated than OH-(aq), I-(aq) ion is preferentially discharged to give iodine solution.
2I-(aq) → I2(aq) + 2e-

Cathode : K+(aq) and H+(aq) ions migrate to the cathode. Since K+(aq) ion cannot be discharge at the cathode, H+(aq) ion is preferentially discharged to give hydrogen gas.
2H+(aq) + 2e- → H2(g)

Answer 2

你呢條問題 問得好唔清楚
concentrated of ions will preventially discharge ge
咁我當佢係dilute ge話 答案就 C
當佢係concentrated 就 D
A, B一定唔會... 除非你用以mercury 做cathod ge electrode

Answer 3

c.
因為當進行個process 既時候,, 會出左potassium ions,, iodide ions,, hydrogen ions 同hydroxide ions... 起chemical cell 入面,, 黐住負極果邊會lose electrons,, 會lose electrons 既只會係iodide ions 同hydroxide ions... 根據electrochemical series,, hydroxide ions 既reducing power 係高過iodide ions,, 所以就會負極出oxygen...
( 4OH¯ →O2 + 2H2O+ 4e¯ )
而另一邊出hydrogen 係因為hydrogen ions 既oxidizing power 高過potassium ions..
( 2H+ + 2e¯ →H2 )