Universiti Tunku Abdul Rahman ( Kampar Campus )

Bachelor of Science (Hons) Biotechnology

Year 1 Semester 1

Group 1

Laboratory 1A ( UESB 1112 )

(II) Atomic Structures and Periodicity

Lecturer: Ms. Chong Foon Yee

Group Member:

1. Ang Pei Wen ( 08AIB02216 )

2. Chan Pei Sin ( 08AIB03544 )

3. Cheah Hong Leong ( 08AIB03788 )

Experiment No. 8

Title: Determination of Nickel by Gravimetric Analysis

Date: 23 July 2008

Title: Determination of Nickel by Gravimetric AnalysisObjectives:

- To determine the amount of nickel in a given salt via gravimetry analysis.- The weight per cent of nickel in salt is calculated and compared with the theoretical

value.

Theory and Background:

The gravimetric analysis is the method used in the field of chemistry which involves the weighing of the reactant and the product, before and after the chemical reaction. The product which is usually of known composition is the precipitate formed from the reaction. The precipitate formed has a very low solubility product, Ksp and thus is very insoluble in water.

The principle of the gravimetric analysis is the formation of the insoluble precipitate from the soluble reactants. The solution will react with an excess of a second reagent and the precipitate of known composition will be formed. The precipitate is then dried and weighed so that the molar quantity of the solution can be determined. In the gravimetric analysis, all the reactants are assumed to react to form the same product (precipitate).

In the gravimetric analysis, the precipitate with larger particle sizes is preferred as they are easier to be collected and they also contain fewer contaminants. The particle a size of the precipitate is depends on the chemical properties of the precipitate and also the condition of the reaction during the precipitation. Besides, the particle size may also affected by the temperature, concentration of the reactant, and also the rate of the second reagent added to the solution.

The process of precipitation consists of two stages: the nucleation and the particle growth. The precipitation is initiated with nucleation stage which is then followed by the particle growth stage. The particle size of the precipitate is depends on the two stages in which one is predominates in the process. If the nucleation process dominates the precipitations process, the average particle size of the precipitate will be very small. If the particle growth dominates the precipitation process, the average particle size of the precipitate will be larger.

Usually, the precipitate formed will be filtrated using the suction pump, Buchner flask and crucible. The mother liquor (the solution from which the precipitate formed) is poured into the crucible which has already covered by layers of filter paper, the suction pump will forces the liquor into the Buchner flask while the precipitate will be filtered on the filter papers. The filtrate is then heated to dehydrate the remaining water.

One of the most popular gravimetric analysis is the determination of nickel by using dimethylgloxime as second reagent. The dimethylgloxime is an organic precipitating agent which is also called chelating agent. The dimethylgloxime will reacts with the nickel ions to form an insoluble precipitate, nickel dimethylgloxime, Ni(C4H7O2N2)2. The precipitate formed from this reaction is also known as coordination compound. The dimethylgloxime has two functional groups that can from dative covalent bonds with the nickel ion by donating a pair of the electrons to the nickel ion.

The using of dimethylgloxime as the precipitating agent has several advantages in gravimetric analysis. The dimethylgloxime will form a precipitate with nickel ions with almost totally specificity. Besides, the precipitate formed, nickel dimethylgloxime is in bright red in color. This makes the experimenter easy to detect if there is any precipitate remaining in the wall of the beaker after all the mother liquor has poured onto the filter papers in the crucible. This indirectly increases the accuracy of the weight of the precipitate measured. Nickel dimethylgloxime, the precipitate is also thermally stable and it can be dried in the oven from 100°C to 110°C without having the risk that it will thermally decomposed into other chemicals.

Experiment Procedures:

Apparatus and Materials- Nickel ammonium sulphate Concentrated HCl Dimethylglyoxime reagent Concentrated ammonia Beaker Glass rod Thermometer Distilled water Water bath Analytical balance Watch glass Filter paper Suction pump Suction funnel

Procedures-

1. Two 0.3-0.4g samples of nickel ammonium sulphate, NiSO4(NH4)2SO4 was weight accurately into 250cm3 beakers. The salt was dissolved in distilled water, 2-3cm3

concentrated HCl was added and diluted to approximately 150cm3.2. Heated to 70-80oC, a slight excess of dimethylglyoxime reagent was added and

concentrated ammonia solution was then added dropwise and constantly stirred until precipitation occurred and completed precipitation in slight excess.

3. The precipitation was digested for 20-30 minutes on the steam bath and the solution was tested for complete precipitation.

4. The precipitation was allowed to stand for one hour to cool. The cold solution was filtered through sintered glass crucible porosity 3, previously dried to constant weight by heating to 100-120oC and weighing after cooling in a desiccator.

5. The precipitate was washed with several small quantities of cold water until free from chloride, and dried it at 110-120oC for 45-60 minutes. Allowed to cool in a desiccator and weigh.

6. The drying was repeated until constant weight is attained. Ni(C4H7O2N2)2 was weigh as which contains 20.32 per cent Nickel.

Experiment Data:

Table: Determination of the Weight of Nickel Ammonium Sulphate and Nickel Dimethylgloxime

Apparatus and Materials Weight (g)Nickel Ammonium Sulphate, NiSO4(NH4)2SO4 0.3152Watch glass + Filter papers (2 layers) + Nickel Dimethylgloxime 32.4069Watch glass + Filter papers (2 layers) 32.2564Nickel Dimethylgloxime, Ni(C4H7O2N2)2 0.1505

Analysis and Calculation:

Relative atomic mass of nickel, Ni = 58.71

Nickel Ammonium Sulphate: NiSO4(NH4)2SO4

Relative molecular mass of Nickel Ammonium Sulphate = 58.71 + 32.06 + 4(16.00) + 2[14.01 + 4(1.01)] + 32.06 + 4(16.00) = 286.93

Percentage of nickel in Nickel Ammonium Sulphate, % = 58.71 x 100% 286.93 = 20.46%

Nickel Dimethylgloxime: Ni(C4H7O2N2)2

Relative molecular mass of Nickel Dimethylgloxime = 58.71 + 2[4(12.01) + 7(1.01) + 2(16.00) + 2(14.01)] = 288.97

Percentage of nickel in Nickel Dimethylgloxime, % = 58.71 x 100% 288.97 = 20.32%

I m not really understands the objective of this exp, so this calculation is hanging here……

Discussion and Precaution:

Discussion-!@#$

Precaution-

Materials such as hydrochloric acid, HCl and concentrated ammonia, NH3 should be handle with care to prevent any unwanted accident to happen since these materials are very corrosive.

Large excess of concentrated ammonia was avoided since it may lead to increasing solubility or contamination of the precipitate, furthermore to avoid the waste of material.

Glass rod was used when pouring Nickel Dimethylgloxime into the suction pump as to guide the solution to be concentrated in the middle of the filter paper.

Two layers of filter paper were used as the suction pump is too powerful and might cause the filter paper to puncture if only one layer was used.

Watch glass was used while weighing the Nickel Dimethylgloxime on the analytical balance to prevent Nickel Dimethylgloxime to spill on the pan.

Conclusion:!@#$

Reference:Seamus P. J. Higson, Analytical Chemistry, Oxford, 2004.

Questions:1. Calculate the weight per cent of nickel in the salt and compare your result with the

theoretical weight per cent.