ammonium back titration?

[RainSakura]

can someone please explain to me how titrating ammonium via back titration would work for a fertiliser, the proceures and calculations involved and most improtantly, the related questions youre likely to get asked(both calc and theory questions)?

[Somye]

titrate NH4 with a base with a known number of mol such as NaOH. After reaction is completed, titrate excess NaOH against HCL of know volume and concentration.

From this, you would first calculate mol of HCL and total NaOH
then, work out how much NaOH reacted in the second reaction through stoichiometric ratios.
minus this amount from original NaOH mol, and you get number of NaOH which reacted in first equation
use stoichiometric ratios to calculate mol of NH4 and hence make calculation of conc. etc.

[dinosaur93]

ok, what if the burette is diluted with water, what would happen to the end result, higher or lower concentration, why?

Same for pipette...

[amilss]

if the burette is rinsed with water it will mean you need to use more of the titrant in order to reach the end point (because it is diluted), so then you're going to over-estimate the concentration of the unknown.

if it's the pipette, you would under-estimate the concentration of the unknown, since the solution gets further diluted, it would require less of the burette solution to reach the end point

[Shenz0r]

This is a back titration, it works differently from a normal titration because when you do the titration you are finding the excess number of mol.

If your burette was rinsed with water (and if you put your excess mol as an aliquot), it would dilute the solution in the burette and more titrant will be used. This will lead to a higher caculated amount of mol in excess. Thus, there will be less amount of mol that reacted with the substance you're analysing, and thus your concentration of the unknown substance will be lower than expected.