A quantitative analysis for ethanol, C2H60, is accomplished by a redox back titration. Ethanol is oxidized to acetic acid, C2H40O2, using excess dichromate, Cr207 2- ', which is reduced to Crt. The excess dichromate is titrated with Fe2*, giving Cr* and Fe3+ as products. In a typical analysis, a 5.00-mL sample of a brandy is diluted to 500 mL in a volumetric flask. A 10.00-mL sample is taken and the ethanol is removed by distillation and collected in 50.00 mL of an 2- acidified solution of 0.0200 M K2Cr207. Titration of the unreacted Cr207 requires 21.48 mL of 0.1014 M Fe2+. Calculate the %w/v ethanol in the brandy. Which is the analyte in this problem? O C2H60 O cr207 2- O C2H402 O Fe2+

A quantitative analysis for ethanol, C2H60, is accomplished by a redox back titration. Ethanol is oxidized to acetic acid, C2H40O2, using excess dichromate, Cr207 2- ', which is reduced to Crt. The excess dichromate is titrated with Fe2, giving Cr and Fe3+ as products. In a typical analysis, a 5.00-mL sample of a brandy is diluted to 500 mL in a volumetric flask. A 10.00-mL sample is taken and the ethanol is removed by distillation and collected in 50.00 mL of an 2- acidified solution of 0.0200 M K2Cr207. Titration of the unreacted Cr207 requires 21.48 mL of 0.1014 M Fe2+. Calculate the %w/v ethanol in the brandy. Which is the analyte in this problem? O C2H60 O cr207 2- O C2H402 O Fe2+

Principles of Modern Chemistry

8th Edition

ISBN:9781305079113

Author:David W. Oxtoby, H. Pat Gillis, Laurie J. Butler

Publisher:David W. Oxtoby, H. Pat Gillis, Laurie J. Butler

Chapter11: Solutions

Section: Chapter Questions

Problem 72AP

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A quantitative analysis for ethanol, C2H6O, can be accomplished by a redox back titration.Ethanol is oxidized to acetic acid, C2H4O2, using excess dichromate, Cr2O72–, which is reduced toCr3+. The excess dichromate is titrated with Fe2+, giving Cr3+ and Fe3+ as products. In a typicalanalysis, a 5.00-mL sample of a brandy is diluted to 500 mL in a volumetric flask. A 10.00-mLsample is taken and the ethanol is removed by distillation and collected in 50.00 mL of anacidified solution of 0.0200 M K2Cr2O7. A back titration of the unreacted Cr2O72–requires 21.48mL of 0.1014 M Fe2+. Calculate the %w/v ethanol in the brandy
The solubility of borax, which is made up of sodium tetraborate (Na2B4O5(OH)4 8H2O), was analyzed. The dissolution of borax is: Na2B4O5(OH)4 • 8H2O(s) ⇌ 2 Na+(aq) + B4O5(OH)42–(aq) + 8 H2O(l) A 50 mL saturated solution was prepared. After filtration of solution, 5 mL aliquot was transferred to a flask and titrated using 0.432 M HCl. The endpoint was found to be 4.73 mL of the titrant. Tetraborate anion (B4O5(OH)42-) is a weak base which reacts with HCl like the following reaction: B4O5(OH)42–(aq) + 2 H+(aq) + 3 H2O(l) ⇌ 4 H3BO3(aq) What is Ksp expression for the dissolution? What is the tetraborate ions concentration in the filtrate? What is the molar solubility and Ksp of borax if the titration was done at room temperature (298 K)?
Fifty food supplement tablets with a total mass of 66.393 g were crushed into powder to analyse the content of FeSO4·7H2O. 2.988 g of the powder were dissolved in HNO3 and heated to convert all the iron to Fe3+. Addition of aqueous NH3 caused quantitative .precipitation of Fe2O3· X H2O, which was ignited to give 0.0640 g of Fe2O3. Determine the average weight of FeSO4·7H2O in each tablet.
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Fifty food supplement tablets with a total mass of 66.393 g were crushed into powder to analyse the content of FeSO4·7H2O. 2.988 g of the powder were dissolved in HNO3 and heated to convert all the iron to Fe3+. Addition of aqueous NH3 caused quantitative precipitation of Fe2O3·xH2O, which was ignited to give 0.0640 g of Fe2O3. Determine the average weight of FeSO4·7H2O in each tablet.
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A student was asked to determine the concentration of ammonia, a volatile substance, in a commercially available cloudy ammonia solution used for cleaning. First the student pipetted 25.00 mL of the cloudy ammonia solution into a 250.0 mL conical flask. 50.00 mL of 0.100 mol L-¹ HCl(aq) was immed added to the conical flask which reactedwith the ammonia in solution. The excess (unreacted) HC1 was then titrated with 21.50 mL 0. 050 M Na2CO3 (aq). Calculate the concentration of the ammonia in the cloudy ammonia solution.
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