N in ammonium sulphate

Determination of N in Ammonium Sulphate

         In fertilisers containing only ammoniacal from of N, the nitrogen can be estimated by (i) distillation with NaOH or (ii) distillation with MgO or formaldehyde filtration method.

Principle

         The NH4-N is liberated from ammoniacal fertilisers by alkali (NaOH or MgO) which is then absorbed in known quantity of standard acid. The amount of such NH3 liberated is calculated from the volume of standard acid consumed.

Reagents

1. Standard 0.1N NaOH / KOH

2. standard 0.1N HCl or H2SO4  

3. Zinc granules

4. NaOH - 40% solution

5. Methyl red indicator solution

Procedure

* Take one gram of ammonium sulphate sample and dissolve in water. Filter if required and make up volume to 250 ml.

* Transfer 10 ml of aliquot to distillation flask. Add 700 ml of water and few glass beads and zinc bits.

* Add 10 ml of 40% NaOH to the distillation flask and close it tightly.

* Immediately connect it to distillation unit keeping the condenser outlet tube dipped in 25 ml of 0.1 N standard H2SO4 / HCl acid in an ice-tumbler with 2-3 drops of methyl red indicator.

* Distil 125 to 150 ml at moderately high temperature. (Test with red litmus paper, it should not turn blue).

* Remove the ice-tumbler and rinse the outlet tube with distilled water.

* Back titrate the excess 0.1 N H2SO4 / HCl against 0.1 N KOH.

* Carry out a blank simultaneously..

         From the difference which gives the volume of H2SO4 Consumed by ammonia, calculate the nitrogen content of the fertiliser and report it as per cent.

Note : 1. While distilling the solution in the ice tumbler, if it turns yellow in the ice tumblers, add again a known quantity (usually 25 ml) of  0.1N H2 SO4 and continue distillation. Do not disturb the set up while adding 0.1N H2SO4.

   2.  Do not lower or remove the burner during distillation. This will lead to back titration of 0.1N H2SO4.

Calculation.

Weight of fertiliser sample   = a g

Volume made up             =250 ml

Volume of aliquot taken              =10 ml

Volume of 0.1 N H2SO4 taken        =25 ml

Volume of 0.1 KOH used    =X ml

Volume of 0.1 N H2SO4 consumed to neutralize the ammonia=25 - X ml

Percentage of nitrogen=

Result

         The nitrogen content in Ammonium Sulphate of the given soil sample is -----------