describe the colour change when aqueous bromine is added to aqueous potassium iodide

when aqueous bromine is added to aqueous potassium iodide a reaction occurs.
the ionic half equations are shown.
Br2(aq) + 2e- => 2Br-(aq)
2I-(aq) => I2(aq) + 2e-
describe the colour change.
original colour of potassium iodide solution.....
final colour of reaction mixture......

i wrote orange to dark brown and my friend wrote colourless to reddish brown

i'm pretty sure i'm wrong but we're nsure of the right answer, pls help my exam is tmrw

Reply 1

Ciel.

Original post by joryk

when aqueous bromine is added to aqueous potassium iodide a reaction occurs.
the ionic half equations are shown.
Br2(aq) + 2e- => 2Br-(aq)
2I-(aq) => I2(aq) + 2e-
describe the colour change.
original colour of potassium iodide solution.....
final colour of reaction mixture......
i wrote orange to dark brown and my friend wrote colourless to reddish brown
i'm pretty sure i'm wrong but we're nsure of the right answer, pls help my exam is tmrw

chat gpt says "the colour changes from colourless to brown as iodine is formed in the reaction."

Reply 2

Ciel.

it also adds "the brown colour formed is typically a reddish-brown or orange-brown shade, depending on the concentration of iodine in the solution."

Reply 3

joryk

Original post by Ciel.

chat gpt says "the colour changes from colourless to brown as iodine is formed in the reaction."

alrighty thank you i got it 👍️

Reply 4

Nitrotoluene

Original post by joryk

alrighty thank you i got it 👍️

Below, you will find some recommendations that will aid in your identification of the color change:
Can you start with the basic evaluation: What should the color of a potassium iodide solution be mainly described as? Be aware of the colors of the most common ionic compounds.
When checking the reactants, you may ask: How does bromine in the aqueous phase appear? It’s a key character in this reaction.
Examine the products closely: A reaction yields bromide ions and iodine as per reactions below. What colors will these have in the liquid phase?

Br2(aq) + 2e- ==>2Br^-(aq)
2I^-(aq) ==> I2(aq) + 2e-

Can you foresee the ultimate outcome: During the progress of the reaction, bromine is depleted while iodine is produced. Which one is going to impart the final color to the mixture?
After reviewing the colors of the reactants and the products, you will be able to see the overall color change of the system clearly.
Here are my two cents!

(edited 2 weeks ago)

Reply 5

TypicalNerd

Original post by joryk

when aqueous bromine is added to aqueous potassium iodide a reaction occurs.
the ionic half equations are shown.
Br2(aq) + 2e- => 2Br-(aq)
2I-(aq) => I2(aq) + 2e-
describe the colour change.
original colour of potassium iodide solution.....
final colour of reaction mixture......
i wrote orange to dark brown and my friend wrote colourless to reddish brown
i'm pretty sure i'm wrong but we're nsure of the right answer, pls help my exam is tmrw

Potassium iodide solution itself is colourless - the simplistic way you can think about this in A level terms is that neither K^+ nor I^- has any partially filled d-subshells and so you don’t get any d-d transitions. Hence, you would generally say the solution is colourless.

Upon addition of bromine, you instantaneously get a redox reaction in which the bromine oxidises iodide ions to iodine:

Br2(aq) + 2I^- (aq) —> I2(aq) + 2Br^-(aq)

The trap here is that there are several colours for iodine that you are expected to learn at A level.

In the solid state, iodine is a shiny grey solid. In organic solvents, iodine forms a purple solution and in inorganic solvents, iodine forms brown solutions (which can be turned blue-black upon the addition of starch).

We are told that the solution is aqueous (so expect the iodine to dissolve and form an aqueous solution - perhaps a bit of an oversimplification, however) and there is no mention of starch (so no need to consider blue-black as the final colour), so the final colour should be brown.

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