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).

I would have to examine your methods, but sulfides (silver sulfides) will be dark.

From the information provided, it seems that you are conducting a test for chlorides in a NaOH sample. To conduct the test, you dissolved 1.0g of NaOH in 5ml of distilled water, acidified it with 4ml of dilute nitric acid, and diluted it to 15ml with distilled water. Then, you poured this mixture into a test tube containing 1ml of AgNO3 solution.

The fact that you obtained a dirty brown precipitate (ppt) upon mixing the NaOH sample with the AgNO3 solution suggests that chlorides might be present in your NaOH sample. The dirty brown color can be attributed to the formation of silver chloride (AgCl). When AgCl is exposed to light, it darkens and turns a dark bluish color with a slight yellow tint, hence the brownish appearance.

However, to confirm that the dirty brown ppt is indeed silver chloride and not another silver halide, such as silver bromide or silver iodide, further testing is required. One way to confirm the presence of silver chloride is to perform a solubility test. This involves adding a small amount of dilute ammonia solution (NH4OH) to the dirty brown ppt. If the ppt dissolves, it confirms the presence of silver chloride, as both silver bromide and silver iodide are insoluble in dilute ammonia solution.

In your control solution of 50ppm sodium chloride, a cloudy white ppt was obtained after standing for a while. This again suggests the presence of silver chloride, as sodium chloride reacts with silver nitrate to form silver chloride.

So, in summary, based on the information provided, it is likely that your NaOH sample contains chlorides, as indicated by the dirty brown ppt obtained upon mixing with AgNO3 solution. To confirm that the ppt is silver chloride and not another silver halide, a solubility test using dilute ammonia solution can be conducted.