April 21, 2015

Homework Help: Analytical chemistry

Posted by Gloria on Saturday, August 3, 2013 at 2:04pm.

Below i wrote a few problems, i did them all but in the book i don't have results, so i don't know if i did them right or not. I would really appreciate if someone would go through the problems and tell me if i got the right results. If i made a mistake somewhere please let me know and i will try to do the problem again.

1. After appropriate preliminary treatment, the thalium in a 10.2 g pesticide sample was precipitated as TlI and was weighted as such. Calculate the percentage of Tl2SO4 (fw=504.8) in the sample if 0.1964 g of TlI (fw=331.27) was recovered.
MY RESULT: 1.47%

2. A 5 g sample of a pesticide was decomposed with metallic sodium in alcohol and the liberated chloride ion was precipitated as AgCl. Express the results of this analysis in terms of the percentage of C14H9Cl5 (fw=354.5) based upon the recovery of 0.1606 g of AgCl.
MY RESULT: 1.59%

3. The nitrobenzene (fw=123) in a 0.739 g sample was determined by dilution with an Hcl/methanol mixture, followed by the introduction of 0.465 g of pure tin. The mixture was refluxed for an hour, during which the nitrobenzene was reduced to aniline:
2C6H5NO2 + 3Sn + 12H -> 2C6H5NH2 + 4H2O + 3Sn
When the reaction was complete the unused tin was isolated by filtration, dried and found to weigh 0.128 g. Calculate the percentage of nitrobenzene in the sample.
MY RESULT: 31.5%

4. Titration of the I2 produced form 0.1238 g of primary-standard KIO3 required 41.27mL of sodium thiosulfate. Calculate the concentration of the Na2S2O3 solution.
MY RESULT: 0.08412 M

5. A 0.1884 g sample of impure Na2Co3 required 31.56 mL of 0.1056 M HCl. Calculate the percent purity of the Na2Co3.
MY RESULT: 0.02216 M

6. The sulfur in a 0.5073 g organic sample was burned in a steam of O2, the combustion products were bubbled through H2O2 to convert SO2 to H2SO4. Titration of the H2So4 required 33.29 Ml of 0.1115 M NaOH. Calculate the percent S in the sample.
MY RESULT: 11.73%

7. Exactly 40Ml of a solution of HClO4 was added to a solution containing 0.4793 g of primary-standard-grade Na2Co3. The solution was boiled to remove CO2 and the excess HClO4 was back-titrated with 8.7 mL of a NaOH solution. In a seperate experiment, 25 mL of NaOH neutralized 27.43 mL of HClO4. Calculate the molarity of the acid and the base.
MY RESULT: acid-0.2969M, base-0.3258

8. A 0.3396 g sample that assayed 96.4% Na2SO4 was titrated with a solution of BaCl2. What is the molarity of the Bacl2 solution if the end point was observed when 35.7 mL of the reagent was added?
MY RESULT: 0.06456 M

9. The thiourea in a 1.455 g sample of organic material was extracted into a dilute H2SO4 solution and titrated with 37.31 mL of 0.009372 M Hg(2+) via the reaction
4(NH2)2CS + Hg -> [(NH2)2CS]4Hg
Calculate the percent (NH2)2CS in the sample.
MY RESULT: 7.51%

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