Prac Write up Analysis of the nitrogen content of lawn fertiliser

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Prac Write up Analysis of the nitrogen content of lawn fertiliser
Analysis of the nitrogen content of lawn fertiliser

1. Aim
To find the percentage by mass of available nitrogen, present as the ammonium ion, in a lawn fertiliser.
2. Materials
1.3g lawn fertiliser, finely ground
100ml standard sodium hydroxide solution (0.96M)
100ml standard hydrochloric acid (0.94M)
Methyl red indicator
500mL de-ionised water
Wash bottle containing de-ionised water
Red litmus paper
2 × small funnels
250 mL volumetric flask
3 × 250mL conical flask
20mL pipette
Pipette filler
5 mL measuring cylinder
Burette and stand
White tile
Electronic heater
Bench mat
Safety glasses
3. Procedure
1) Accurately weigh about 1.3g of fertiliser.

2) Transfer the sample of fertiliser to a 250mL volumetric flask. Rinse the weighing bottle with a bit of distilled water and add this to the contents of the volumetric flask. Add more water until the flask is almost half full, stop and swirl the contents to dissolve the ammonium compounds in the fertiliser. Add more water to make up the volume of the solution to reach calibration line. Mix thoroughly.

3) Using a 20mL pipette, dispense aliquots of the fertiliser solution into each of three 250mL conical flasks.

4) Thoroughly wash the pipette and rinse with a small volume of standard sodium hydroxide solution. Place a 20.00mL aliquot of sodium hydroxide solution in each of the flasks containing fertiliser solution. Record the concentration of the standard solution of sodium hydroxide.

5) To all of the flasks add 50mL of distilled water

6) Boil the 3 bottles of mixture for about 10 mins. If needed, add more water to maintain constant volume of solution while boiling. Test the vapour at the neck of the flask with a moist strip of red litmus paper. If ammonia is still present the paper will turn blue and heating should continue until the litmus paper no longer detects ammonia. Cool the flask once completed.

7) Rinse and fill a burette with standard hydrochloric

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