University Of Karachi

CHEMICAL PROCESS TECHNOLOGY

(Practical file)

Syed Saad AhmedB-0933040B.E 3rd Year

Chemical Engineering

Submitted To:Ma’am Khehkashan

CHEMICAL PROCESS TECHNOLOGY 2012

Experiment no. 8

OBJECT:

Estimation of Phosphate in Phosphate fertilizer

REAGENTS:

Phosphate fertilizer. HNO320%, 0.1N HNO3 and concentrated HNO3. 20% KNO3 solution. 0.1NNaOH solution. Phenolphthalein indicator. 5% Ammonium Molybdate solution.

THEORY:

When a solution of phosphate is treated with an excess of ammonium molybdate solution a precipitate is obtained, which after washing is converted into ammonium molybdate phosphate with the composition (NH4)3.[PO4.12MoO3] this may be titrated with standard sodium hydroxide solution using phenolphthalein as an indicator, but the end point is rather poor due to the liberation of ammonia.

REACTIONS:

[PO4 .12MoO3 ]+26NaOH⟶NaHPO4+12Na2MoO 4+14H 2O

PROCEDURE:

Weigh accurately 1.00 gram of the ammonium phosphate fertilizer. Dissolve in a minimum amount of concentrated HNO3 and make up to the volume with distilled water in a 100 ml volumetric flask. Take 10 ml of the solution in a beaker. Add 10 ml of 20% HNO3 and 30 ml of 5% ammonium molybdate solution. Shake and stir vigorously and allow the precipitate to settle for 20 minutes. Filter and wash the fine precipitate with 20% KNO3 solution till free from acid. Pierce a whole through the filter paper and completely dissolve all the precipitated yellow ammonium phosphomolybdate in 100 ml of 0.1 N NaOHsolution, dilute with distilled water. Add 3-4 drops of phenolphthalein and titrate to colorless end point with 0.1 N HNO3. Check the end point by adding 1 drop of 0.1 N NaOH which should restore the pink color.

Note:

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CHEMICAL PROCESS TECHNOLOGY 2012

Precipitate of yellow ammonium phosphomolybdate is very slow to form scratching of the sides of the beaker facilitates precipitation. Standard 0.1 N NaOH and standard 0.1 N HNO3 should be prepared by

titrating NaOH against standard succinic acid and HNO3 against standard Na2CO3 or NaOH.

CALCULATIONS:

To calculate the amount and weight % of Phosphorous in the given sample:

Amount of 0.1 N HNO3 used in titration = 15.5 ml

Amount of 0.1 N NaOH available from titration = (15.5 x 0.1 N) / 0.1 N = 15.5 ml

Hence,

Amount of 0.1 N NaOH consumed to form NaHPO4 = (100 – 15.5) = 84.5 ml

Now,

1000 ml of NaOH = 84.5 / 26 = 3.25 gram

84.5 ml of 0.1 N NaOH = 3.25 x (84.5/1000) x (0.1N/ N)

84.5 ml of 0.1 N NaOH = 3.25 x (84.5/1000 x 10) = 0.027 gram

Therefore amount of PO4 = (119/95) x 0.027 = 0.0338 gram

Percentage of Phosphate∈Phosphate fertilizer=0.03381

×100

Percentage of Phosphate∈Phosphate fertilizer=3.38%

RESULTS:

Amount of phosphate in 1 gram phosphate fertilizer is 0.0338 gram. (3.38%)

DISCUSSION:

Phosphate fertilizers are produced by adding acid to ground or pulverized phosphate rock. If sulfuric acid is used, single or normal, phosphate (SSP) is produced, with a phosphorus content of 16–21% as phosphorous pentoxide (P2O5). If

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CHEMICAL PROCESS TECHNOLOGY 2012

phosphoric acid is used to acidulate the phosphate rock, triple phosphate (TSP) is the result. TSP has a phosphorus content of 43–48% as P2O5.Normal superphosphate, also referred to as ordinary superphosphate, is no longer used in large quantities. Because of its lower analysis and high transportation costs, it has been replaced by concentrated superphosphate (46 percent P2O5,) and the ammonium phosphates.

Research:Researchers are warning that inappropriate management of phosphate fertilizer and animal manure in China has resulted in serious water pollution and substantial waste of phosphorus.

REFERENCE:

UNIDO (United Nations Industrial Development Organization). 1978. Process Technologies for Phosphate Fertilizers. New York.

www.1ifc.org/wps/wcm/connect/.../phosfer_PPAH.pdf?MOD www.fieldcrop.msu.edu/uploads/documents/ Phosphate %20 Fertilizers .pdf http://www.nature.com/news/2010/100929/full/news.2010.498.html

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