Answer to Question #5313 in Physical Chemistry for Jen

Question

0.144 g of an aluminium compound X react with an excess of water to produce a gas. This gas burns completely in O2 to form H2O and 72cm3 of CO2 only. Volume of CO2 was measured at room temperature and pressure. Deduce the formula of X

Answer 1

X - Al_xC_y;
Al_xC_y + H₂O = Al(OH)₃↓ + CH₄↑;
CH₄ + 2O₂ = CO₂ + 2H₂O;
ν(CH₄) = 0.072/22.4 = 0.0032mol;
Because the valence of Al is 3, and the valence of C is 4 and z is taken as coefficient of proportionality, then Μ(Al_xC_y) = 26*4z+12*3z;
We have the next equation: 0.0032/3 = 0.144/26*4z + 12*3z;
0.001 = 0.144/140z;
z=1.
So, formula of X is Al₄C₃.