When 19.0 g of copper reacted with nitrogen, 20.45 g of copper nitride were produced - Leaving Cert Chemistry - Question e - 2015

Next, we calculate the moles of nitrogen in copper nitride (Cu_xN_y). First, we find the mass of nitrogen in the compound:

Mass of nitrogen = Total mass of copper nitride - Mass of copper

$20.45 \text{ g} - 19.0 \text{ g} = 1.45 \text{ g}$

Now, we convert the mass of nitrogen to moles:

The molar mass of nitrogen (N) is approximately 14 g/mol. Thus,

$\text{Moles of N} = \frac{1.45 \text{ g}}{14 \text{ g/mol}} \approx 0.1036 \text{ moles} \approx 0.10 \text{ moles}$

Now, we have the moles for copper and nitrogen:

• Moles of Cu = 0.3
• Moles of N = 0.10

To find the simplest mole ratio, we divide each by the smallest number of moles:

$\frac{0.3 \text{ moles Cu}}{0.10} = 3$
$\frac{0.10 \text{ moles N}}{0.10} = 1$

Thus, the ratio of copper to nitrogen is 3:1. Therefore, the empirical formula for copper nitride is:

Cu₃N