Chemistry Question

Question

Laws that were passed in some states in the country define a drunk driver as one who drives with a blood alcohol level of 0.10% by mass or higher. The level of alcohol can be determined by titrating blood plasma with potassium dichromate according to the unbalanced redox reaction. "H+ + Cr2O72- + C2H5OH = Cr3+ + CO2 + H" if the only substance that reacts with the dichromate in blood plasma is alcohol, is a person legally drunk if 38.94 ML of 0.0723M potassium dichromate is required to titrate 50.0 g sample of blood plasma?

Answer 1

First we will balance the equation

2Cr₂O₇^2- + C₂H₅OH + 16H⁺ = 4Cr³⁺ + 2CO₂ + 11H₂O

Next, we'll find the mols of dichromate used in the sample

38.94 ml x 1L/1000 m x0.0723 mol/L = 2.815x10^-3 mol

Then find mols of ethanol present in the sample

2.815x10^-3 mol Cr₂O₇^2- x 1 mol C₂H₅OH / 2 mol Cr₂O₇^2- = 5.631x10^-3 mol C2H5OH

Converting this to grams we have 5.631x10^-3 mol C2H5OH x 46 g / mol = 0.259 g

Finding % by mass we have...

0.259 g / 50.0 g (x100%) = 0.52%