Question

A 39.90 gram sample of copper is heated in the presence of excess oxygen. A metal oxide is formed with a mass of44.92 g. Determine the empirical formula of the metal oxide.

Answer 1

m = 39.90 g of Cu

MW Cu = 63.5

m = 44.92 CuOx

determine empiricla formula

th eequation:

Cu + O2 --> CuO

identify mol of Cu

mol Cu = masS/MW = 39.90/63.5 = 0.6283464 mol of Cu

CuO could be either

CuO or Cu2O

MW of Cu2O = 143.09

MW of CuO = 79.545

then

find mol ratios:

if Cu2O then mol = mass/MW = 44.92/143.09 = 0.3139; wchich as 0.6278 mol of Cu

if CuO then mol = mass/MW = 44.92/79.545 = 0.56471, which has 0.56471 mol of Cu

since previously we got 0.6283464 mol of Cu

the right answer msut be Cu2O