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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: Vad3rmort on May 12, 2019, 03:00:04 AM

Title: Reaction of potassium iodide in diluted H2SO4 at room temperature
Post by: Vad3rmort on May 12, 2019, 03:00:04 AM

Hey all,
First time poster here, so please be patient and kind! As the title suggests, I'm trying to understand what reactions are happening when I dissolve potassium iodide in 1M sulphuric acid at room temperature. I've tried researching but mostly found resources of reactions with concentrated sulphuric acid or at boiling temperatures. Any explanations or resources that I have missed are muchly appreciated, thanks!

Title: Re: Reaction of potassium iodide in diluted H2SO4 at room temperature
Post by: AWK on May 12, 2019, 03:12:24 AM

Nothing observed.
Redox reaction proceeds with  >40 % sulphuric acid.

Title: Re: Reaction of potassium iodide in diluted H2SO4 at room temperature
Post by: Vad3rmort on May 12, 2019, 06:25:28 AM

Interesting...so what does it mean if my solution is progressively getting browner (dark) in color as the days progress from light yellow. My guess is the formation of iodine I2 causing the change in color, but what are the other products being formed? Thanks for your prompt response AWK. (https://i.imgur.com/ydiUowY.jpg)

Title: Re: Reaction of potassium iodide in diluted H2SO4 at room temperature
Post by: AWK on May 12, 2019, 06:38:30 AM

Potassium iodide also changes color in the light, but slower.

Title: Re: Reaction of potassium iodide in diluted H2SO4 at room temperature
Post by: Vad3rmort on May 12, 2019, 08:22:34 AM

Thanks AWK, I shall confirm that by keeping a new solution in a dark cupboard. Any ideas what kind of products I should expect with this photolytic degradation?

Title: Re: Reaction of potassium iodide in diluted H2SO4 at room temperature
Post by: AWK on May 12, 2019, 08:54:34 AM

Reaction H₂ + I₂  :requil: 2HI
is reversible.
Note also hydroiodic acid also easily change color in the light.