Question

when a mixture of acetone and propanal is burnt, 4.48 liters of carbon dioxide are produced at STP. What is the mass of water produced at the same time?

Answer 1

Acetone and propanal are functional isomers having the same molecular formula C₃H₆O but different functional groups:

This means that both compounds have the same equation of combustion:

C₃H₆O + 4O₂ = 3CO₂ + 3H₂O

Using ideal gas law pV=nRT we can find number of moles of carbon dioxide:

$n(CO_2) = \frac{pV}{RT} = \frac {101325Pa \cdot 0.00448m^3}{8.314\frac{J}{mol \cdot K}\cdot 273.15K} = 0.2 mol$

According to stoichiometry of the reaction

$n(H_2O) = n(CO_2) = 0.2 mol$

Thus mass of water produced in this reaction is

$m(H_2O) = n(H_2O)\cdot M(H_2O) = 0.2 mol \cdot 18\frac{g}{mol} = 3.6g$