A person\'s blood alcohol (C 2 H 5 OH) level can be determined by titrating a sa

Question

A person's blood alcohol (C2H5OH) level can be determined by titrating a sample of blood plasma with a potassium dichromate solution. The balanced equation is

A person's blood alcohol (C2H5OH) level can be determined by titrating a sample of blood plasma with a potassium dichromate solution. The balanced equation is 16 H+(aq) + 2 Cr2O72-(aq) + C2H5OH(aq) rightarrow 4 Cr3+(aq) + 2 CO2(g) + 11 H2O(l) If 32.94 mL of 0.05928 M Cr2O72- is required to titrate 28.95 g plasma, what is the mass percent of alcohol in the blood?

Explanation / Answer

Take the volume of dichromate and multiply by the molar concentration to find out how many moles of dichromate you used.

32.94*0.05928= 1.952moles

Looking at your chemical reaction, you can see that one ethanol molecule was titrated for every 2 dichromates.

So divide the number of moles of dichromate by 2

=1.952/2=0.962 moles

0.962 moles of ethanol were titrated.

Multiply this by the molecular mass of ethanol (46.07g/mol)

= 0.962*46.07 = 44.964grams.

Now divide this by the mass of the plasma

(28.95g/44.964)= 0.6438mass percent.= 64.38%

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