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October 1, 2014

Homework Help: Chemistry - pls help

Posted by candy on Wednesday, September 22, 2010 at 5:31pm.

This is a limit test for chlorides.
1.0g of NaOH sample was dissolved in 5ml of deionized water, acidified with 4ml of dilute nitric acid and diluted to 15ml with deionized water. (Test tube A)
10ml of 50ppm Standard NaCl solution was prepared. 5ml of water was added, follwed by 1ml of dilute nitric acid. (Test tube B)
1ml of AgNO3 was added to each of the test tubes and compared for opalescence.

Test tube A (with NaOH sample) gave a dirty brown ppt.
Test tube A (standard NaCl solution) gave a cloudy ppt characteristic of the AgCl formed.

Does this mean my sample contains chlorides?

Thanks.


Posted by candy on Tuesday, September 21, 2010 at 4:56pm.


I obtained a lot of dirty brown ppt the moment the mixture was poured into AgNO3 solution. Does this mean my NaOH sample contains a lot of chlorides? Could other silver halides be present?

However for my control solution of 50ppm sodium chloride solution,a cloudy white ppt was obtained after standing for a while.

Please advise how should I conduct the test?


Posted by candy on Tuesday, September 21, 2010 at 4:05pm.


This is a test for chlorides in NaOH sample.
1.0g of NaOH was dissolved in 5ml of distilled water, acidified with 4ml of dilute nitric acid and diluted to 15ml with distilled water. This mixture was poured into a test tube containing 1ml of AgNO3 solution.
However, I obtained a dirty brown ppt. Do you have any idea what the problem might be?
Thanks.




Chemistry - help - bobpursley, Tuesday, September 21, 2010 at 4:12pm
Yes. You did this in light, the silver chloride is photosenstive, it darkens when exposed to light. Brown is not unusual (dark bluish, with slight yellow).









Chemistry - more advice needed thanks - bobpursley, Tuesday, September 21, 2010 at 5:23pm
I would have to examine your methods, but sulfides (silver sulfides) will be dark.

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