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Determination Of Nickel By Gravimetric Analysis

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Introduction

Title : Determination of Nickel by Gravimetric Analysis Objective : * To determine the amount of nickel in a given salt. * To calculate the weight percent of nickel in the salt and to compare with the Theoretical value * To study the gravimetric analysis method to determine the compound in a certain unknown salt Introduction and background Gravimetric analysis is a technique through which the amount of an analyte (the ion being analyzed) can be determined through the measurement of mass. Gravimetric analysis depend on comparing the masses of two compounds containing the analyte. The basic method of gravimetric analysis is fairly straightforward. A weighed sample is dissolved after which an excess of a precipitating agent is added. The precipitate which forms is filtered, dried or ignited and weighed. From the mass and known composition of the precipitate, the amount of the original ion can be determined. For successful determinations a few criteria must be met. First, the desired substance must be completely precipitated. In most determinations the precipitate is of such low solubility that losses from dissolution are negligible. An additional factor is the "common ion" effect, this further reduces the solubility of the precipitate. ...read more.

Middle

beaker + filtrate + filter paper 150.82g 156.64g Weight of filtrate 0.4299g 0.1826g Average weight of filtrate = (0.4299g + 0.1826g)/ 2 = 0.3063 g Calculation & Analysis Molecular weight of nickel ammonium sulphate salt (NiSO4(NH4)2SO4?6H2O) = 394.69g/mol Molecular weight of dmG = 116.11g/mol Molecular weight of Ni(dmgH)2 = 288.69g/mol Molecular weight of Nickel = 58.69 g/mol Gravimetric factor of nickel in precipitate = 58.69 g/mol � 288.69 g/mol = 0.2032 The reaction of the formation of chelate is given by the chemical equation below, Ni2+ + 2CH3(CNOH)2 CH3 +NH3/H2O --> Ni(dmgH)2 From the equation, 1 mole of nickel salt should produce 1 mole of Ni(dmgH)2 Mole of Nickel salt (theoretical) = 0.3471g � 394.69g/mol = 0.000879mol Theoretically, 1 mole of salt can produce 1 mole of Ni(dmgH)2 So, that means 0.000879mol of salt should produce = 0.000879mol of Ni(dmgH)2 But, Mole of Ni(dmgH)2 (Practical) = 0.3063g � 288.69g/mol = 1.06 x 10-3mol The data shows that the practical value is more than theoretical value. Weight of Ni(dmgH)2 (Practical)= 1.06 x 10-3mol x 288.69g/mol = 0.3063g Weight of nickel from salt = 0.000879mol x 58.69g/mol = 0.051g Per cent of nickel in precipitate = (0.2032 x 0.3063g X 100) ...read more.

Conclusion

The advantage of gravimetric analysis is that if the procedures are followed carefully, it provides for exceedingly precise and accurate analysis. It provides very little possibilities for instrumental error and does not require a series of standards for calculation of an unknown. This method does not require expensive equipment. However, it has few disadvantages. One of the disadvantages is that this method is time consuming. We also found that each step in Gravimetric analysis method must be done cautiously because a small mistake during the process can affect the end result. Precaution steps: 1. This experiment is very time consuming. Therefore, the experiment should be planned ahead carefully to avoid wasting time. In that way, time could be saved and the experiment can be conducted systematically. 2. Since highly concentrated HCl is used in this experiment, care should be exercised. 3. The filtrate should not be stored wet in the dessicator. The filtrate should only be placed in the dessicator after the filtrate is dried in the oven for at least 30-40 minutes. Conclusion We successfully obtained Ni(dmgH)2 by using the Gravimetric analysis method. The amount of Ni(dmgH)2 we obtained from the experiment is 0.427g and 0.1793g from sample A and sample B respectively.The weight per cent of nickel in precipitate is 25.17 and 10.69 for sample A and sample B respectively. ...read more.

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4 star(s)

Mark: 4/5
This is a very good report. A solid introduction is presented and an excellent discussion has been written. The aims of the experiment are clear and calculations are well presented.

To gain 5/5, questions 3 and 4 must be answered. Also, better referencing throughout the report is necessary, as well as better formatting.

Marked by teacher Kathryn Bradley 24/09/2012

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