Potassium Iodide + Conc Sulphuric Acid

In an exam question regarding this reaction, it states that a mixture of gases are eveolved as a result of the reaction, (HI, Hydrogen Sulphide??) It states that one observation is 'misty white fumes' - which gas would be responsible for these? The markscheme states that the HI would, But i thought taht all hydrogen halides are colourless???
Also, it asks for one other observation, and the markscheme states black/brown solid/liquid (the iodine) or purple vapour, what is this purple vapour???

thanks

Reply 1

No Future

17

1. The hydrogen halide would be misty, I guess. Misty/white IS colourless.

2. I2 is purple vapour - if the I2 was in gaseous form.

:smile:

Hope that helps.

Reply 2

dhugga

OP

1

ah i see, thank u :smile:

Reply 3

No Future

17

No problem :smile:

Reply 4

Tes

4

the hydrogen halides are colourless, but when they are in gaseous form and mix with moist (any water will do) air they react to form misty white droplets of acid in the air.

Reply 5

Excalibur

15

I think you also get brown liquid due to the I₃- triodide ion forming.

Reply 6

sufiankane

2

dhugga

In an exam question regarding this reaction, it states that a mixture of gases are eveolved as a result of the reaction, (HI, Hydrogen Sulphide??) It states that one observation is 'misty white fumes' - which gas would be responsible for these? The markscheme states that the HI would, But i thought taht all hydrogen halides are colourless???
Also, it asks for one other observation, and the markscheme states black/brown solid/liquid (the iodine) or purple vapour, what is this purple vapour???

thanks

definitely not hydrogen sulphide, isnt that really really toxic and makes you cough loads and loads?

Reply 7

Tes

4

Actually hydrogen sulphide is formed!

H2SO4 + 8I- + 8H+ ==> 4I2 + H2S + 4H2O

Thats why the reaction can smell of bad eggs

Reply 8

Excalibur

15

NaI + H₂SO₄ --> HI + NaHSO₄
8HI + H₂SO₄ --> 4I₂ + H₂S + 4H₂O
6HI + H₂SO₄ --> 3I₂ + S + 4H₂O
2HI + H₂SO₄ --> I₂ + SO₂ + 2H₂O

You get a bit of HI (steamy white fumes in moist air) but not a usable amount. You also get violet iodine vapour. You get some yellow solid due to sulphur forming. You get the smell of bad eggs from hydrogen sulphide. You also get a brown sludgy solution, due to the tri-iodide forming.

Reply 9

Tes

4

how did you subscript the numbers

Reply 10

Excalibur

15

<sub></sub>, replace sharp brackets with square brackets [].

Potassium Iodide + Conc Sulphuric Acid

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