Question

Tungsten occurs in nature as calcium tungstate which is converted, after mining it, to tungstic acid. Tungsten is then extracted from the tungstic acid by the following (unbalanced) reaction: H2 (g) + H2WO4 (aq) → W (s) + H2O (g). How many moles of hydrogen are needed to prepare 1 kg of tungsten?5.44 mol16.32 mol32.64 mol10.90 mol

Answer 1

$Balanced\text{ }chemical\text{ }equation:3H_{2(g)}+H_2WO_{4(aq)}\rightarrow W_{(s)}+4H_2O_{(g)}$

We will convert the mass of tungsten into moles:

$\begin{gathered} 1kg=1000g \\ _nW=\frac{mass}{molar\text{ }mass} \\ _nW=\frac{1000g}{183.84gmol^{-1}} \\ _nW=5.44mol \end{gathered}$

Based on the chemical equation 3 moles of hydrogen produces 1 mole tungsten. We will use this information to determine the moles of hydrogen needed to produce 5.44 moles of tungsten:

$5.44mol\text{ }W\times\frac{3mol\text{ }H_2}{1mol\text{ }W}=16.32mol\text{ }H_2$

Answer: 16.32mol H2 is needed to prepare 1kg tungsten.