The Determination of Phosphate in Beverage

Practical Report Cover Sheet

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University of Zululand

Faculty of Science and Agriculture

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                Department of Chemistry PRACTICAL REPORT COVER SHEET

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Contents

AIM        3

INTRODUCTION        3

PROCEDURE        4

RESULTS        6

DISCUSSION        8

CONCLUSSION        9

REFERENCES        9

AIM

The aim of this experiment is to determine the amount of phosphate in a beverage

INTRODUCTION

Phosphoric acid is one of the weak acids that are found in carbonated beverages. It is a component of all cola soft drinks and it has a much higher concentration than the other acids that exists in a container of soft drink. Cola beverages are the most widely consumed drink and the most popular among students.

Phosphoric acid is a typical polyfunctional acid. In aqueous solution, it undergoes the following three dissociation reactions (1):  

H3PO4 + H2O => H2PO4- + H3O+           Ka1 = 7.11 x 10-3

H2PO4- + H2O => HPO42- + H3O+           Ka2 = 6.32 x 10-8

HPO42- + H2O => PO43- + H3O+            Ka3 = 4.5 x 10-13

The phosphate ion, (PO43-), is an inorganic chemical derivative of phosphoric acid and also it is the conjugate base that has the ability to form many different salts. In organic chemistry, a phosphate, also called organophosphate, is an ester of phosphoric acid. These organic phosphates are important in biochemistry and biogeochemistry, and inorganic phosphates are mined to obtain phosphorus for use in agriculture and industry. It is a polyatomic ion with a molar mass of 94.97 g/mol and empirical formula PO43− and it consists of one phosphorus atom in the center which is surrounded by four oxygen atoms forming a tetrahedral geometry. A phosphate salt is formed when a positively charged ion is attached to the negatively charged oxygen atoms of the ion, forming an ionic compound. Many of the known phosphates are insoluble in water at standard temperature and pressure. The hydrogen and dihydrogen phosphates are slightly more soluble than the corresponding phosphates (2).

Ammonium molybdate is a colorless inorganic compound with the chemical formula (NH4)6Mo7O24. It is harmful and if swallowed or inhaled it causes irritation to the eyes, skin, and respiratory tract. It also affects kidneys and blood. Ammonium metavanadate is a white the inorganic solid with the formula NH4VO3, although samples are often yellow due to impurities of V2O5. It is often used as an intermediate in the purification of vanadium.

Phosphorus–molybdate complex: On reaction of phosphate ions with molybdate, the phosphorus–molybdate complex is formed. Its concentration is determined directly (without reduction) at 340nm. Molybdivanadophosphate: Phosphate concentration can be determined by reaction of the phosphate ions with vanadium molybdenum heteropolyacid (without reduction) (3).