Answer to Question #110270 in General Chemistry for Ash

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.