Blood Alcohol Levels

Blood alcohol levels can be determined from a redox reaction with potassium dichromate according to the balanced equation…

C2H5OH(aq)+2Cr2O7^2-(aq)+16H^+(aq)—->2CO2(g)+4Cr^3+(aq)+11H2O(l)

What is the blood alcohol level in mass percent if 8.76mL of .04988M K2Cr2O7 is required for complete reaction with a 10.002g sample of blood?

What Is The Mass Percent?

The metal content of iron in ores can be determined by a redox procedure in which the sample is first oxidized with Br2 to convert all the iron to Fe^3+ and then titrated with Sn^2+ to reduce the Fe^3+ to Fe^2+.  The balanced equation is:

2Fe^3+(aq)+Sn^2+(aq)—->2Fe^2+(aq)+Sn^4+(aq)

What is the mass percent of Fe in a .1875g sample of ore if 13.28mL of a .1015M Sn^2+ solution is needed to titrate the Fe^3+?

What Is The Molar Concentration?

What is the molar concentration of As(III) in a solution if 22.35mL of .100M KBrO3 is needed for complete reaction with 50.00mL of the As(III) solution?  The balanced equation is…

3H3AsO3(aq)+BrO3^-(aq)—->Br^-(aq)+3H3AsO4(aq)

What Is The Concentration?

Dichromate ion, Cr2O7^2-, reacts with aqueous iron(III) ion in acidic solution according to the balanced equation

Cr2O7^2-(aq)+Fe^2+(aq)+14H^+(aq)—->2Cr^3+(aq)+6Fe^3+(aq)+7H20(l)

 

What is the concentration of Fe^2+ if 46.99mL of .2004M K2Cr2O7 is needed to titrate 

50.00mL of the Fe^2+ solution?

 

Redox Titrations

Iodine, I2, reacts with aqueous thiosulfate ion in neutral solution according to the balance equation

I2(aq)+2S2O3^2-(aq)—->S4O6^2-(aq)+2I^-(aq)

How many grams of I2 are present in a solution if 35.20mL of .15M Na2S2O3 solution is needed to titrate the I2 solution?

 

Precipitation Titration

An example of a precipitation titration reaction is the Mohr method, which is used to find the concentration of halide ions in solution (particularly Cl− and Br−). First, the sample to be analyzed is titrated with a AgNO3 solution, which results in the precipitation of a white silver solid (e.g., AgCl). Because it is difficult to tell when all the halide ions have reacted with the silver ions, a small amount of an indicator ion, CrO42−, is added to the reaction. Because Ag2CrO4 is more soluble thanAgCl, the Ag2CrO4 precipitates out only after all of the Cl− ions have precipitated out as AgCl. Thus, as soon as all of the Cl− ions have reacted, the Ag2CrO4 precipitation begins, marking the equivalence point of the reaction by forming a rust-colored precipitate.

As a food chemist for a major potato chip company, you are responsible for determining the salt content of new potato chip products for the packaging label. The potato chips are seasoned with table salt, NaCl. You weigh out a handful of the chips, boil them in water to extract the salt, and then filter the boiled chips to remove the soggy chip pieces. You then analyze the chip filtrate for Cl−concentration using the Mohr method.

First you prepare a solution of silver nitrate, AgNO3, and titrate it against 0.500 g of KCl using the Mohr method. You find that it takes 64.2mL of AgNO3 titrant to reach the equivalence point of the reaction.

You then use the same silver nitrate solution to analyze the chip filtrate in a Mohr reaction, finding that the solution yields a rusty brown precipitate when 48.8mL of titrant is added.

If the sample of chips used to make the filtrate weighed 90.5g , how much NaCl is present in one serving (155g ) of chips?

Unbalanced Oxidation and Reduction Half-Reactions

Write unbalanced oxidation half-reaction for the following process.

Mn3+(aq)→MnO2(s)+Mn2+(aq)

Write unbalanced reduction half-reaction for the following process.

Mn3+(aq)→MnO2(s)+Mn2+(aq)

Unbalanced Oxidation and Reduction Equations

Write unbalanced oxidation half-reaction for the following process.

Fe2O3(s)+CO(g)→Fe(s)+CO2(g)

Write unbalanced reduction half-reaction for the following process.

Fe2O3(s)+CO(g)→Fe(s)+CO2(g)

Calculating Mass Percent

The metal content of iron in ores can be determined by a redox procedure in which the sample is first oxidized with Br2 to convert all the iron to Fe3+ and then titrated with Sn2+ to reduce the Fe3+ to Fe2+. The balanced equation is
2Fe3+(aq)+Sn2+(aq)→2Fe2+(aq)+Sn4+(aq)

What is the mass percent Fe in a 0.1900g sample if 12.50mL of a 0.1015 M Sn2+ solution is needed to titrate the Fe3+?

Molar Concentration

What is the molar concentration of Br^- ions in a 0.225M (aq) solution of FeBr3, assuming complete dissociation?