gravimetric determination of phosphorus in

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I. Abstract

The objective of this test is to determinethe Phophorus articles of fertilizer samples applying Gravimetric Research. It requires dissolution from the fertilizer sample, precipitation and heating and cooling from the sample. Pooled standard deviations of the two data units for % Pwet, %Pdry, %P2O5 wet and %P2O5 dry had been 5. 1448, 5. 1472, 11. 8436 and 11. 8504 respectvely. During the experiment a data rejection for %P and %P2O5 was determined at around 20% and 47%. Dedication of the Phosphorus content in fertilizer is important in quality assurance and in the choosing of the fertilizer quality important for culture.

II. Introduction

Vegetation require essential goodness such as Nitrogen, Phosphorus, Potassium or Sulfur to increase. However , the majority of soils shortage these macronutrients thus a decrease in meals production. In connection with this, the usage of fertilizers made up of these macronutrients has been area of the agricultural tradition. Fertilizers have in its product labels a set of quantities, known as the fertilizer grade that usually appear in the proper execution N-P-K, implies the proportions of essential nutrients present (ie 10-10-10 which means 10% Nitrogen, 10% Phosphate in the form of P2O5, 10% Potassium in the form of K2O).

Different companies worldwide like Association of American Plant Foodstuff Control Officials (AAPFCO) in america, conduct distinct tests to evaluate the reliability and regularity of the nutrient content with respect to that of the product labeled and also to make sure quality assurance as part of consumer privileges. Analysis of fertilizer can be conducted applying Gravimetric Research.

In Gravimetric Analysis, the item with well-known composition is resulted from the conversion in the analyte into a soluble precipitate that can be very easily filtered and it is free from pollutants by subjecting it to heat. This product of well-known composition are weighed plus the percentage in the analyte in the sample can be discovered. In this test, the analyte, Phosphorus inside the fertilizer will probably be precipitated because Magnesium Ammonium Phosphate Hexahydrate, MgNH4PO4 ( 6H2O:

5H2O + HPO42- + NH4+ + Mg2+ + OH- ( MgNH4PO4 ( 6H2O (s) (1)

The purpose of this experiment is to determine the percentage of Phosphorus (P) and Diphosphorus (P2O5) in the fertilizer sample by means of Gravimetric Analysis.

3. Data and Results

In this experiment, the wet (as received) and dry dumbbells of the fertilizer sample, from the previous research of wetness determination of the same fertilizer test were employed. Weights had been divided into two data pieces, Data Set 1 having four (4) trials and Data Collection 2 having three (3) trials.

The dried sample from the past experiment that moisture was determined, was dissolved and is also converted into a occassionaly soluble precipitate, MgNH4PO4 ( 6H2O which is then strained and weighed. The filtration system paper utilized was weighed to easily decide the excess weight of the medicine. The precipitate was in that case dried and weighed.

IV. Debate

This test aims to determine the percentage of P and P2O5 in fertilizer sample using Gravimetry. The fertilizer sample from the previous test of Moisture Determination was utilized in this kind of experiment. The dried fertilizer sample was dissolved with 40 mL distilled drinking water and was then filtered to obtain a clear filtrate.

In Gravimetry, it is crucial to use a precipitating agent that if certainly not specific, must be selective and would give out a precipitate containing the analyte. This kind of precipitating agent should also give out a medications that is conveniently filtered and washed via impurities, unreactive with the elements present in the atmosphere, of low solubility to lessen losing analyte during filtration and washing, and with known composition after drying or heating. In cases like this, 45 milliliters of 10% MgSO4 ( 7H2O was added to the filtrate, with 150 milliliters 2M NH3 as the precipitating agent to obtain the preferred precipitate MgNH4PO4 ( 6H2O which provides the analyte P. See Equation 1 . Whilst other precipitating agent like NH4Cl can be used, NH3 utilized otherwise to ensure that the desired medications would be type. The presence of Cl- ions can more likely to appeal to Mg2+ thus producing MgCl2 precipitates, which do not contain the analyte in this experiment which is S.

It should be noted that NH3 is usually added gradually with continuous stirring to the solution to assure the growth in the precipitate, bringing on a medications that is much easier to filter and become freed of impurities. This technique is related to the von Weirman’s ratio where the compound size of a precipitate is inversely proportionate to the worth of Comparative Superaturation given by:

Relative Supersaturation = [pic]


Q= focus of reactants before anticipation

S= solubility from the precipitate

Precipitates are both formed by simply nucleation, or perhaps by molecule growth. In nucleation, contaminants join jointly to form a large mass, generally a result of supersaturation in alternatives. It involves huge amount of precipitate, yet , is composed of tiny particles which can be hard to filter. Through this experiment, what is desired is definitely particle growth that brings a precipitate of large size but of smaller amount. This is likely by even more precipitation wherein particles stick to the surface of initially nucleated particles. The supersaturation state of the solution is eased during constant stirring after addition from the precipitating agent, thus endorsing particle expansion rather nucleation. With respect to the von Weirman’s proportion, the higher the importance of the rate, the higher the potential of getting smaller debris, thereby endorsing nucleation, unlike a lower benefit of the percentage which stimulates particle progress that will deliver larger precipitates that is essential in this research.

After the addition of the precipitating agent with constant stir, the mixture was allowed to stand at room heat for 15 mins. It is important to let the mixture stand, without any turmoil or external forces acting on it to let digestion to occur. Digestion is important to allow reprecipitation, wherein contaminants will adhere to the in the beginning small precipitates, and to expel water elements thus decreasing the surface region available for adsorbent which causes pollutants to obtain greater particles with greater chastity and less difficult filterability.

After 15 mins, the mix was strained using the preweighed filter daily news. The filtration system paper that was preweighed was kept in the dessicator until further use to maintain the moisture by adhering to the filter daily news. Preweighing the filter newspaper was helpful for easy determination of the weigth of the medicine. During filtration, precipitate was washed with distilled drinking water in tiny portions of 5mL two times. For each cleaning, the unadulterated water was poured into the beaker wherever precipitation occured to accumulate the rest of the precipitates that adhered to the sides with the beaker.

Following washing with distilled water, two 10mL portions of 95% ethanol were used for second cleansing. The use of 95% ethanol, becaue of its volatility thus will dry out the medicine faster, will ensure that no longer water can be trapped inside the pores between precipitates, nominal solubility loss and allergens of little size will not likely loosen up and pass through the pores from the filter conventional paper. Smaller portions of the rinse liquid had been used to make certain that the precipitate will still be intact and nosignificant loss inside the amount from the precipitate due to the overflowing of washes water.

The filtration paper made up of the precipitate was in that case heated in the oven established a to 110ËšC intended for 1 hour and was cooled down in a dessicator for 15 min. After this, the excess weight of the medicine was dependant upon subtracting the significance of the preweighed filter daily news with the fat of the filtration paper such as the precipitate.

Although Gravimetry is known as as one of the efficient and less high-priced ways of deciding a fertilizer component, this system is still not fool proof and mistakes due to espective, definite and indeterminate factors can result in an erroneous result. One of these errors may be the fast addition of the precipitating agent and low impact of agitation leading to the development of much larger amount of small debris that may move across the filter paper therefore having lesser amount of precipitate, and a lower worth for the P or perhaps P2O5 content material in the test. On the other hand, as while the blend stands in room temperature without the coverings, pollutants like dust particles may be included in the mixture, adding to weight for the precipitate, giving a higher yield. This excessive yield gives a S or P2O5 content of the sample higher than its actual benefit.

It can be observed from Desk 3 which the range of % P and % P2O5 lies among approximately 6% to 13% and 15% to thirty percent respectively with 20% and 47% shady values mainly because it is almost double of the beliefs in range. By executing the Q test, the values were confirmed to be accpetable with regards to the real value and values inside the population, or rejected. Desk 4. one particular and four. 2 displays the beliefs that were rejected and accepted for each data set. Notice that the twenty percent and 47% for % P and % P2O5 respectively, both belonging to Data Set 1 were rejected with 95% confidence level, which means that the Qexp exceeded the significance of the Qtabulated.

Of all the studies in both Data Collection 1 and 2, the group with values similar to that of the rejected principles were those obtained the greatest amount of precipitate. Observe Table 2 . This being rejected or errounous error inside the data could be attributed to the determinate and indeterminate errors in the try things out. One more problem that could be the real reason for this rejection is the personal error when it comes to the browsing of the analytical balance. As well, because of this being rejected in data, aside from the fact that Data Arranged 2 offers lower volume of population, Data Set a couple of parameters intended for Measure of Accuracy are nearer to each other, while using dried examples having greater values than that of the wet sample. Iti s because dried out sample will be purer than that of the wet sample containing continue to moisture and other interfering agent to getting the actual % G and % P2O5.

V. Summary and Conclusions

With this experiment, it had been determined the fertilizer sample has % P array of 6% to 13% with % P2O5 from 15% to thirty percent. However , the standard types of fertilizers with phosphates contain a minimum of forty two. 5 % water sencillo phosphate and 46% total phosphate by weight, as with the case of Triple Superphosphate or eighty-five % normal water soluble and 20% obtainable in Superphosphate. It should be noted that the theoretical values will be different depending on the form of fertilizer utilized in the try things out.

Despite the info rejection that occurred, general, it can be declared that the test is a achievement since the aims of the test such as doing gravimetric analysis in the willpower of phosphorus content also to know the basic principle in splitting up by anticipation were attained.

Yet, we recommend that there would be a unique manner of putting the precipitating agent, just like addition dropwise or certain amounts per second or perhaps stirring in order to ensure the correct formation of crystals necessary by the experiment. It should also be observed that upon digestion, or letting the combination stand with out agitation, the mixture should be covered to avoid impurities present in the ambiance.

VI. Recommendations

Chapter a few: Gravimetry. Cal State College or university, Dominguez Hills. <>Accessed 17 January 2013.

Fischer, R. W. and Peters, D. G. Quantitative Chemical Analysis 3rd ed. late 1960s; pp42-43; forty-nine

Food and Agriculture Organization of the Un. AGP ” Fertilizer Specs. Utilized 04 January 2013.

Rehm, G. ain al. Understanding Phosphorus Fertilizers: Phophorus inside the Agricultural Environment. University of Minnesota: Extendable. 2010. <>Accessed 18 January 2013.

Skoog, M. et ing. Fundamentals of Analytical Biochemistry and biology 6th education. Saunder College Publishing. 1992; pp72-80


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