My answer of 67% is wrong - I misread the question and thought it was butane-2,3-diol - sorry about that.
When I do the calculations for butane-1,2-diol and
assume that formic acid is oxidised to CO2
by permanganate, I get 44% glycerol (mole ratio). The method is the same as yours, but I use 2x + 1.2y= 0.028 because I think the formic acid formed in the periodate cleavage of glycerol will react with permanganate. If
it is true that you can ignore the formic acid from the oxidative cleavage of glycerol and
that formaldehyde is oxidised to CO2
, then your answer is correct. However, I do not think you can do that - my opinion is below if you are interested:
If you are assuming that formic acid does not react with permanganate, then you should work on the assumption that formaldehyde is oxidised to formic acid (not CO2
), because formaldehyde is oxidised to CO2
in two steps via formic acid:
Formaldehyde + oxidant
Formic acid (eq 1)
Formic acid + oxidant
If we can ignore the formic acid produced in the reaction of periodate with glycerol, then we are saying that eq 2 does not happen. Therefore any formaldehyde from the periodate step is oxidised only to the formic acid level based on the first assumption. If we do this, then the equation is 0.8x + 0.8y = 0.028. Solving the simultaneous equations gives a nonsense answer.
I admit that the question does say that the "aldehyde groups were titrated...", but I think this is unrealistic. If permanganate oxidises formaldehyde to CO2
, then it follows that any formic acid in the system will also affect the titration.