Testing for nitrates and phosphates (1 Viewer)

[ND]

Would this work for phosphates:

Add HCl, add barium chloride, filter to remove barium sulfate, add ammonia, add barium chloride, filter, dry, and weigh barium phosphate.

Is the addition of HCl enough to ensure that no phosphate is precipitated, and that all sulfate is precipitated out?

Also how can you get a quantitative reading of nitrate present? I don't think tests for either of these are addressed in CC.

 

[Constip8edSkunk]

hmm do we need 2 know quantitative analysis of phosphate?

think its to keep phosphate from precipitating (something to do with the equilibrium with hydrogen phosphate and etc???)... not sure about ensuring all sulfate precipitates... and the process looks ok... i could be totally, completely, utterly wrong though....

also i thinking skipping that first part and just add concentrated ammonia would work as well? - again not sure


nitrate can be converted to nitrite and then tested using colorimetry... by adding something(argh so need 2 revise chem) that makes it go pink

 

[ND]

Originally posted by Constip8edSkunk
hmm do we need 2 know quantitative analysis of phosphate?

think its to keep phosphate from precipitating (something to do with the equilibrium with hydrogen phosphate and etc???)... not sure about ensuring all sulfate precipitates... and the process looks ok... i could be totally, completely, utterly wrong though....

also i thinking skipping that first part and just add concentrated ammonia would work as well? - again not sure


nitrate can be converted to nitrite and then tested using colorimetry... by adding something(argh so need 2 revise chem) that makes it go pink

I think we'd need the quantitative phosphate and nitrate for the monitoring eutophication dotpoint.

The reason i thought to precipitate out the sulfate first is so none precipitated out with the phosphate. But i suppose there's just as much chance losing phosphate with the sulfate.

I'll check out that nitrite thing. Thanks.

 

[jims]

in the pathways book they have the kjeldahl method for nitrates. its involes back titration or something; i can never remember the proceedure, just the name.
for phosphate, they have the molydenum blue method. add a strong oxidant (nitric/sulfuric acid digestion) to convert all the phosphorus compounds to phosphate. then add molydate ions which turns blue. then use colorimetry to determine the conc of phos.
for qualitative tests, they have: add Ca(NO3)2 to make CaPO4

 

[+:: $i[Q]u3 ::+]

molybdenum blue method:
add ammonium molybdate - this forms a pale yellow complex with the phosphate ions.
then add ascorbic acid (vitC) which causes it to turn an intense blue colour
measure light absorbed by solution. (colorimetry)

kjeldahl - for organic nitrogen.
convert all N to ammonium sulfate by boiling with conc sulfuric acid. Add excess alkali, then distil ammonia formed, titrate with known amount of standardised acid and back titration.

colorimetry for nitrates/nitrites.
reduce nitrates to nitrites by flowing solution thru a column of granulated cadmium.
add two different reagents, which causes the solution to form a purple-pink azo-dye.
measure light absorbed. (colorimetry)

 

[ND]

Thanks!