Outline the Procedure of measuring the concentration of nitrates and phosphates in a water sample (3 marks)
[Hint: Kjedahl test]
Woah, I thought this thread had died because nobody posted for over a day and I log in now and there's like 5 new pages haha
Anyway, what is this test? I've never heard of it before this thread and someone mentioned it before as well. Do we need to know this?
The
nitrate concentration in water sample is measured using the
Kjeldahl digestion method.
1) The water sample is boiled with
concentration sulphuric acid to convert the nitrogen into
ammonium sulphate.
2) It is then reacted with
NaOH to form
ammonia.
(NH4)2SO4(aq) + 2NaOH(aq) ------> Na2SO4(aq) + 2NH3(g)+ 2H2O (l)
3) Then,
excess HCl of known concentration and volume (standard solution) is then added to the solution which is then
back titrated to determine the concentration of nitrogen in the sample which is used to determine the nitrate concentration.
Furthermore, to determine/measure the concentration of
phosphates,
colorimetry is used.
1) A measured quantity of
ammonium molybdate along with Nessler's reagent (catalyst) is added to the water sample and is mixed to form a
yellow complex with phosphate known as phosphomolybbdate
2) Then
ascorbic acid is added, reducing the intensity of the yellow complex to become an
intense blue colour.
3) A
colorimetry with the appropriate wavelength is selected and is shined through the sample.
4) The absorbance is calculated wwith a
standard solution and the total phosphate concentration is determined since absorbance is proportional to concentration.
Then add this to make your answer look pretty and complete: nitrates and phosphates need to be monitored to prevent the incidence of algal blooms and cyanobacteria which can cause a high BOD of water, indicating eutrophication which makes the water unusable for any purposes.
Shouldn't take long, just memorise that
