Question

a 5.05 gram sample of a copper substance was heated in air and 6.32g of copper II oxide was formed. What was the formula of the original copper substance?

Answer 1

We're not sure if the copper is pure so we use the following:
\[2CuX+O_2 => 2CuO +2X\]
To determine the amount of O_2 added we subtract the weight of the copper substance from the weight of the Copper II Oxide.
\[6.32g-5.05g=1.27g O_2\]
Now we can determine the moles of O_2:
\[1.27gO_2\frac{1 mol O_2}{31.9988g O_2}=0.0397molO_2\]
Now that we have the moles of O_2 we can calculate the moles of Cu.
\[0.0794molCu\frac{63.546gCu}{1molCu}=5.05gCu\]
Not this is the value of our original substance so the original substance is pure copper.

Answer 2

*Note