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.
I am wondering if you diluted the NaOH with Nitric acid.
Here is my thinking:
1gNaOH/40=.025moles
Now, if you used .004liters of Nitric acid, what was its concentration?
.004*X=.025
x=6.25M
Ok that is dilute. Normally, one would use a standardized solution of 6M, so it wouldn't quite acidify the 1gram NaOH.
So, if OH ions were left, and you added Silver ions, some AgOH would be formed. AgOH is a thick, dark TAN precipate. Some would call this brown. I don't think you acified the solution: did you check the pH?
Doesn't my 4ml HNO3 acidify the solution?
What should I do then? Add another 1ml of dilute Nitric acid?
Based on the information provided, it seems that your NaOH sample does contain chlorides. The dirty brown precipitate formed when the mixture was poured into the AgNO3 solution indicates the presence of chlorides.
Regarding other silver halides possibly being present, it is unlikely because typically only AgCl forms a cloudy precipitate under these conditions.
If you want to conduct the test more accurately, make sure to perform the test in a dark environment since silver chloride is photosensitive and can darken when exposed to light. Additionally, keep in mind that other dark compounds such as silver sulfides can also form dark precipitates.
Based on the information provided, it seems that both the NaOH sample and the standard NaCl solution produced precipitates when mixed with AgNO3.
Test tube A, containing the NaOH sample, resulted in a dirty brown precipitate when mixed with AgNO3. This could indicate the presence of chlorides in the NaOH sample. However, it is important to note that brown precipitates can also be caused by other silver halides or even sulfides.
On the other hand, the control solution of the 50ppm sodium chloride solution produced a cloudy white precipitate, which is characteristic of AgCl formation. This suggests that the standard NaCl solution does contain chlorides.
To conduct the test accurately and confirm the presence of chlorides in the NaOH sample, it is crucial to make sure that the experiment is carried out under proper conditions to minimize interference. Here are some suggestions:
1. Prepare the NaOH sample by dissolving 1.0g of NaOH in 5ml of deionized water, acidify it with 4ml of dilute nitric acid, and then dilute it to 15ml with deionized water.
2. Prepare the standard NaCl solution by taking 10ml of a 50ppm NaCl solution and adding 5ml of water, followed by 1ml of dilute nitric acid.
3. Ensure that the experiment is conducted in a controlled environment, protected from direct light exposure. This is because silver chloride is photosensitive and can darken when exposed to light.
4. Add 1ml of AgNO3 solution to each test tube (both the NaOH sample and the standard NaCl solution) and observe the resulting precipitates.
If the NaOH sample consistently produces a dirty brown precipitate, it indicates the presence of chlorides. However, to confirm the presence of chlorides and rule out other possible interference, it would be advisable to perform additional confirmatory tests like the silver nitrate titration or gravimetric analysis.