a little help on volumetric analysis errors

[Zahta]

I did an prac

on volumetric analysis the nitrogen content  in a fertilliser  and I'm am getting a percentage by mass of nitrogen to be less than the ammonium  ions  which is 12.3% and  my results of nitrogen is more i got 13.4% i did not rinse any of the equipment duch as burette. the teachet said.it was clean do dont worry and we can assume we did rinse the equipment. what errors can contribute to the larger
 perecentage of nitrogen in my results, and also is the hcl the standard solution and is the primary solution  is the fertilliser

[Shenz0r]

Which solution did you put into the burette? If your HCl concentration was accurately known it would be your standard solution, and hence your fertiliser would be the unknown solution.

Chances are, your HCl was put in the burette, which you didn't rinse. This means that there could have been impurities that reacted with your HCl while it was in the burette, and hence a greater number of mol of HCl is needed to neutralise the unknown solution. This would lead to a greater calculated number of mol of whatever you're analysing, and hence you will get a greater mass than expected.

[Zahta]

yes thankyou so much   , also whar are some modification for back titration volumetric anaylsis