Analysis of the nitrogen content of lawn fertiliser

[dinosaur93]

At some stage in the procedure of a back titration, you'll be ask to add 50ml of de-ionised water in each of the flasks. Boil the mixture for about 15 mins. If neccessary, add more water to maintain a constant volume of solution while boiling. Test the vapour at the neck of the flasks wih a moist strip of red litus paper. If ammonia is present, the paper will turn blue and heating should be continued until the point where litmus paper does not detect the presence of ammonia. Once this point has been reached, cool the flasks under running water.

NH₄⁺ + OH^- ---> NH₃ + H₂O
NaOH + HCl ----> NaCl + H₂O

Why was it necessary to cool the flask? What is its purpose.


After having made your standard solution (based from your primary standard), take 20ml aliquot of the fertiliser into 3 250mL conical flasks and 20.0mL aliquot of standard sodium hydroxide solution into each of the flasks containing fertiliser solution.

What would happen to your result and findings if the student taking the aliquot use the same pipette for both solution? Will there be any changes, How?