[a123456]

A: Sublimation

B: Adding water, stirring and filtering

C: Adding water, followed by simple distillation

D: Adding water, stirring and using a separating funnel

[Borek]

Please read the forum rules. You have to show your attempts at answering the question/solving the problem to receive help, it is a forum policy.

[a123456]

The answer I was provided was sublimation. This makes sense because iodine can sublime, and we can collect it using an inverted funnel which is cooled, such that the iodine vapours condense on it.

However, sodium iodide is soluble in water, and iodine is not soluble in water. Hence I don't understand why we cannot separate by dissolving in water, stirring, then filtering (Option B).

Thanks.

[Orcio_87]

https://en.wikipedia.org/wiki/Iodine

Elemental iodine is slightly soluble in water, with one gram dissolving in 3450 ml at 20 °C and 1280 ml at 50 °C; potassium iodide may be added to increase solubility via formation of triiodide ions, among other polyiodides.

I₂ has low solubility, but NaI₃ is quite soluble.

[a123456]

Hi Orcio_87,

I'm not sure how it addresses my question. I'm wondering why adding water, stirring and filtering is not a viable option, since the correct answer given was sublimation.

Thanks.

https://en.wikipedia.org/wiki/Iodine

Elemental iodine is slightly soluble in water, with one gram dissolving in 3450 ml at 20 °C and 1280 ml at 50 °C; potassium iodide may be added to increase solubility via formation of triiodide ions, among other polyiodides.

I₂ has low solubility, but NaI₃ is quite soluble.

[Borek]

I^- + I₂ I₃^-

[rjb]

Hi Orcio_87,

I'm not sure how it addresses my question. I'm wondering why adding water, stirring and filtering is not a viable option, since the correct answer given was sublimation.

Thanks.

As is, the original question is a little bit clumsy; especially if you are a bit of a pedant!

Whilst Iodine has low solubility in water, its solubility (as pointed out in Borek's last post) is increased in the presence of the iodide ion due to the formation of the triiodide ion. This would mean that the option B method would yield fairly pure iodine (left behind in the filter), but impure sodium iodide contaminated with Iodine. This method although possibly 'viable', would require further steps (perhaps sublimation!) for complete separation.

By contrast the sublimation method could yield pure iodine and pretty damn pure potassium iodide.

Seems pretty clear to me...

 

[a123456]

OK, I get it now. Thanks for the help.

Hi Orcio_87,

I'm not sure how it addresses my question. I'm wondering why adding water, stirring and filtering is not a viable option, since the correct answer given was sublimation.

Thanks.

As is, the original question is a little bit clumsy; especially if you are a bit of a pedant!

Whilst Iodine has low solubility in water, its solubility (as pointed out in Borek's last post) is increased in the presence of the iodide ion due to the formation of the triiodide ion. This would mean that the option B method would yield fairly pure iodine (left behind in the filter), but impure sodium iodide contaminated with Iodine. This method although possibly 'viable', would require further steps (perhaps sublimation!) for complete separation.

By contrast the sublimation method could yield pure iodine and pretty damn pure potassium iodide.

Seems pretty clear to me...