Gravimetric Determination of Nickel in Nickel Oxide PDF

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Experiment 2 Gravimetric Determination of Nickel in Nickel Oxide

Abstract Gravimetric analysis is considered one of the most accurate analytical techniques which uses a precipitation method to measure the change in mass. The precipitation reagent used in experiment 2 is nickel dimethylglyoxime which is a specific reagent as it only binds and precipitates Ni ion. The main objective of the lab is to analyze how accurate the analytical technique actually is.We found a yield of 58% and 15.2% from sample 1 and 2 respectively with an average yield of 36.6%. Introduction: Gravimetric analysis is considered one of the most accurate analytical techniques in determining the mass of an ion or analyte in an unknown compound. This is done by measuring the change in mass. For experiment two, the purpose is to determine as accurately as possible the percentage of nickel in an unknown sample of nickel oxide through gravimetric analysis. Then statistics must be used to determine the precision of the results. We determine the mass of the nickel ion in a pure compound and that value is used to mass percentage of the ion in a known quantity of an impure compound. Method: 1. Obtain two medium porosity filtering crucibles and check them for pinhole leaks. 2. Weigh accurately two samples of about 0.1 gram each of the unknown into 400 mL beakers. These masses must be recorded. 3. Dissolve each sample in about 30 mL of 1.0 M hydrochloric acid, HCl. This will take about 30 minutes on a hot plate. After dissolution, a very slight residue may remain, but do not filter the solution. Must use a graduated cylinder. 4. Dilute each sample to 220 mL with hot deionized water. 5. Using a graduated cylinder, very slowly add 15 mL of 1 % alcoholic dimethylglyoxime. Care must be taken to control the amount of excess alcoholic dimethylglyoxime used. If too much is added, the alcohol can become sufficient to dissolve appreciable amounts of the Ni(H2C4H6O2N2)2 which leads to low results. 6. Slowly add 15ml, with stirring, enough 7 M ammonium hydroxide, NH4OH. to make the solution basic. Make sure that the crucibles are dry and ensure to take the mass of empty crucibles. 7. Coagulate the precipitate on a hot plate for at least 30 minutes. Check the supernatant liquid for completeness of precipitation. 8. Filter through the medium porosity filtering crucibles using suction. It helps to have a glass stir rod to hold back the precipitate while clear fluid is poured through the filter.

9. Rinse the precipitate with deionized water. 10. Leave the crucible in a green box. 11. Cool and weigh as Ni(H2C4H6O2N2)2 which contains 20.32% Ni (Formula weight = 288.921). 12. Calculate and report the % Ni in each unknown sample. Work must be shown. 13. Calculate the mean, standard deviation, % RSD, and the 90% confidence limits of the mean.

Results and calculations :

Mass of unknown and known samples Sample 1

Sample 2

Mass of sample (g)

0.111

0.150

Mass of Ni(H2C4H6O2N2)2

0.317

0.1125

Mass of Ni in sample

0.0644

0.0229

Mass of empty crucibles: 30.422g Mass with product for sample 1: 30.7398g 1. %Ni in sample 1: Molar mass of Ni(H2C4H6O2N2)2 = 288.921g Given mass of Ni(H2C4H6O2N2)2 = 30.7398-30.422 = 0.317g Therefore Mol of Ni(H2C4H6O2N2)2 = 0.317/288.921 = 1.0972*10^-3 mo Due to 1:1 , mol of Ni is = mol of Ni(H2C4H6O2N2)2 Therefore, mass of Ni= (1.0972*10^-3)*58.6934=0.0644g So % of Ni in sample 1 is (0.0644/0.111)*100%= 58% 2. Similarly, for sample 2 the mol of Ni(H2C4H6O2N2)2= 3.89*10^-4 Mass of Ni= 3.89*10^-4 * 58.6932=0.0229g Therefore, % of Ni in sample 2 is= (0.0229/0.150)*100%= 15.2% 3. mean= 58+15.2/2= 36.6% 4. %RSD:

s=Square root of ((58-36.6)^2+(15.2-36.6)^2/1) =30.3 Therefore, 30.3/36.6 *1000 = 827 5. 90% confidence level= 36.6+/- ((6.314 * 30.3)/square root of 2)) =36.6+/- 136

Conclusions: The sample 1 results conclude that the yield of Ni in the unknown sample was quite high. Due to time constraint of the lab as well as the delay of the filter, the entire sample one could not be filtered. This would be a cause for lower yield. Sample two could not be processed at all and the data was provided by the TA. Overall the process is quite accurate as we can see that even though there was a lack of proper sampling and filtration, we see a sufficient deposit of nickel in the porosity filters. Systematic errors like clogged porosity filters and old and worn out pipes caused the delay of the filtration and these could be prevented if the quality of the instruments are improved. The mean shows a lower than 50% yield. This could be due to evaporation when heating or loss of product when transferring beakers during the experimental procedure. Sufficient loss of product is caused due to the tendency of Ni(H2C4H6O2N2)2 to stick along the sides of the beaker as well as on the glass stir rod. References: CHEM 3251 Experiment 2 Gravimetric Determination of Nickel in Nickel Oxide Lab manual 2021, Mechref ,Yehia pp 1-10...