7/21/2019 Gravimetric Determination of Phosporus in Fertilizer Samples Chem 28

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GRAVIMETRIC DETERMINATION OF PHOSPORUS IN FERTILIZERSAMPLESSubmitted By: Frances Abegail G. Quezon

Gravimetric analysis is the process where the mass of the product isused to calculate for the mass of the analyte. !"  #n this e$periment%gravimetric analysis is used to determine the amount of phosporus in a givenfertilizer sample. &he same sample from e$periment ' was used. &hepertinent chemical reaction in this e$periment is:

()'* + ),*-' + /)-

+ +0g'+ +*)  0g/)-,*- 1)'*2s3 2!3 '"

As shown above% the reaction proceeds only in basic medium. &his iswhy /)4 was used since it dissociates to form /)-

+ and *) ions. /)-5l is anacidic salt% therefore it cannot be used as a substitute for /)4.

 &he type of gravimetry used in this e$periment is precipitationgravimetry. &his type of gravimetry separates the analyte from the solutionas a precipitate and converts it to a compound of 6nown composition that canbe weighed. 4"

 &he steps of precipitation gravimetry are as stated: preparation of thesolution% precipitation% digestion% washing and filtering the precipitate% dryingand ignition% and weighing.-"  #n the e$periment% the fertilizer solids weredissolved with -7 m8 disilled water and the solids were filtered. &his part isthe solution preparation in precipitation gravimetry. &he supernate was

reacted with 0gS*-9)'* and /)4. pon the first addition% moleculesaggregate to form a nucleous and further addition of reagent would yield tomore nucleous or build up on e$isting nuclei to from a precipitate. &his can bepredicted by the ;on <eirman ratio that states that relative supersaturationis inversely proportional to particle size. Slowly adding the reagent% in thiscase /)4% yields a lower value for relative supersaturation% therefore giveslarger particles.-" &hese larger particles are easier to filter and there are less

chances that some precipitate would accidentally =oin the supernate duringthe filtration. &he reaction yielded a white precipitate that was left to stand for !(

minutes. &he !( minutes allotted for digestion is important because digestioninvolves dissolution of and reprecipitation of particles resulting to betterprecipitate characteristics. #t allows the particles to stay with their origins%thus enabling them to react further and form larger crystals at the e$pense ofsmaller ones. -" &he precipitate was filtered and then washed with water andethanol% heated% and then weighed in the analytical balance.

 &he precipitate% 0g/)-,*-1)'* was washed with >(? ethanol afterdistilled water because ethanol is more volatile and would evaporate afterthe washing later on% as opposed with water.

 &abulated below are possible sources of errors in the e$periment:Table 1. Sources o Errors

Error Eec! o" P#os$orusDe!er%&"a!&o"

Some supernate was spilled duringthe second filtration process

8ower phosporus levels would bedetermined

Some 0g/)-,*-1)'* precipitatewas still left on the walls of the

8ower phosporus levels would bedetermined

7/21/2019 Gravimetric Determination of Phosporus in Fertilizer Samples Chem 28

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bea6er after the ethanol and distilledwater washings

Some 0g/)-,*-1)'* precipitatewas spilled during the transfer to the

dessicator

8ower phosporus levels would bedetermined

 &he goal of the e$periment is to calculate the , content of the samplein the form of ,'*(. *ne of the data computed for ,'*( percent content did notpass the Qtest at >(? confidence level and therefore should not be includedin the computations. &his re=ected data is 4-.>>'?. &he average ,'*( percentcontent of the sample is '@.>@! 7.77>. &his has a percent error of -(?compared to the theoretical value of '7?. &he standard deviation value is7.7-. &his is a low value% meaning that the data is precise% but =udging fromthe percent error% the data is not accurate.

REFERENCES!")arris% . Quantitative Chemical Analysis (th ed. <.). Freeman and5ompany: /ew Cor6% '77!.'"#nstitute of 5hemistry. Quantitative Inorganic Analysis Laboratory Manual 4" Faculty of ,harmacy. http:DDwww.phar.6ufauniv.comDstaffDaymenD!.pdf2accessed April '(% '7!43.-"#slamic niversity of Gaza. http:DDwww.monzirpal.netD5hem?'7'4!7D5ontentsD GravimetricEAnalysis.htm 2accessed April '(% '7!43.