Problem 1

The element gallium (Ga,

Z=31

) is recovered as a by-product of aluminium production. Gallium nitride is made by heating

\ce{Ga2O3}

with ammonia:

\ce{Ga2O3 + 2NH3 -> 2GaN + 3H2O}

. Calculate the mass of

\ce{Ga2O3}

needed to prepare 100 g of GaN. (

M(\ce{Ga2O3}) = 187.4

g mol

^{-1}

M(\ce{GaN}) = 83.7

g mol

^{-1}

)

Step 1 of 3: Moles of product

Intuition

Divide the target mass by the molar mass to get the amount in moles.

n(\ce{GaN}) = \dfrac{100}{83.7} = 1.195\ \text{mol}

Analysis

$n(\ce{GaN}) = m/M = 100\ \text{g}/83.7\ \text{g mol}^{-1} = 1.195$ mol.