Question

An organic compound whose common name is pyrogallol is known to consist only of carbon, hydrogen, and oxygen. Analysis shows it to be 57.14% carbon, 4.80% hydrogen, 38.06% oxygen by mass. In a separate experiment, the molecular mass was determined to be 126 amu. Determine the empirical formula for pyrogallol. Express your answer in the form CxHyOz, replacing x,y, and z with appropriate numerals.

Answer 1

Solution.

w(C) = 57.14%;

w(H) = 4.80%;

w(O) = 38.06%;

x:y:z =(w(C)/A_r(C)):(w(H)/A_r(H)):(w(O)/A_r(O));

x:y:z = ( 0.5714/12):(0.048/1):(0.3806/16) = 0.0476:0.048:0.0238 = 2:2:1;

It is therefore the simplest formula of an organic compound С₂Н₂O;

M(C₂H₂O) = 24+2+16 = 42 amu;

This formula is not true because M(C2H2O) =42 amu , but not 126 amu;

42$\sdot$ a = 126; a = 3;

The compound formula has the form: C₆H₆O₃;

Answer: C₆H₆O₃.