[sambasi]

I am new to this site. I find it very useful.

I have to prepare a mixture of (KI + KBr) by dissolving 10  grams of  KI  and 15 grams of KBr in 1litre of water. I want to know what will be the change in volume of water solution after both KI and KBr are dissolved.

Thanks!
Sambasi

[Borek]

Pretty hard to tell. The best approach is to check experimentally.

In general you would need density tables (determined experimentally). However, while density tables for KI and KBr solutions are not that difficult to find, they would not suffice - for exact result you would need density tables for mixed solutions. And I haven't seen these, ever.

Solutions containing either 25 g of KBr of 25 g of KI in 1000 g of water have volume of 1009 mL, so for any mix I would not expect the result to be substantially different.

[sambasi]

Thank you Borek.
With your input, I may be able to calculate the volume of required (KI + KBr) solution to be added in the process. Thanks once again.

[Borek]

Note: these are 1% changes in volume, they are most likely negligible.

[sambasi]

I got perfect clarity Mr.Borek.

I need additional help. How to check the (I) purity of KI salt and (ii) purity of KBr. salt. The suppliers specify > 98%. How to verify this in lab?

Thanks!

Sambasi

[Borek]

Not as easy one might think, especially if you don't know whet the impurities are. You can try to determine Br^- and I^-:

http://www.titrations.info/precipitation-titration-argentometry-chlorides-Mohr

http://www.titrations.info/iodometric-titration

(in the latter case, just add excess iodate to convert iodides to iodine).

This is not a really good approach, as even small errors can show you have - say - 101% of the iodide in iodide. Much better approach is to determine amount of impurities, and assume whatever is left is your main compound - but you can't do that not knowing impurities identity.

[sambasi]

Dear Mr.Borek,
Thank you for your valuable response and guidance.
 
Regarding the impurities, the following are given as impurities , by the supplier in their product specification. Kindly advise me which impurities are critical to be checked and their test-methods

POTASSIUM BROMIDE –
Loss on drying ( 110 0C, 2 hours ) 0.5 %
Chloride ( Cl ) 0.45 %
Sulphate ( SO4 ) 0.005 %
Iron ( Fe ) 0.002 %
Bromate ( BrO3 ) 0.001 %
Total Nitrogen ( N ) 0.001%
Heavy metals ( as Pb ) 0.001 %
 
POTASSIUM IODIDE
Loss on drying ( 110 0C, 2 hours ) 0.5 %
Sulphate ( SO4 ) 0.005 %
Iodate ( IO3 ) 0.0003 %
Heavy metals ( as Pb ) 0.001 %

I sincerely appreciate your help and also this forum  for having experts who readily share their knowledge.

 

[Borek]

Sorry, that's a whole book to be written.

[sambasi]

Thanks