Question

If 1.0 g of hydrogen reacts completely with 19.0 g of fluorine, what is the percent by mass of hydrogen in the compound that is formed?

Answer 1

Answer : The mass of hydrogen in the compound that is formed are, 5 %

Explanation : Given,

Mass of hydrogen = 1 g

Mass of fluorine = 19 g

Molar mass of hydrogen = 2 g/mole

Molar mass of fluorine = 38 g/mole

First we have to calculate the moles of hydrogen and fluorine.

$\text{Moles of }H_2=\frac{\text{Mass of }H_2}{\text{Molar mass of }H_2}=\frac{1g}{2g/mole}=0.5moles$

$\text{Moles of }F_2=\frac{\text{Mass of }F_2}{\text{Molar mass of }F_2}=\frac{19g}{38g/mole}=0.5moles$

Now we have to calculate the moles of HF.

The balanced chemical reaction is,

$H_2+F_2\rightarrow 2HF$

From the balanced reaction we conclude that

As, 1 mole of $H_2$ react to give 2 moles of $HF$

So, 0.5 mole of $H_2$ react to give $0.5\times 2=1$ moles of $HF$

Now we have to calculate the percent by mass of hydrogen in the compound.

$\text{Percent by mass of hydrogen}=\frac{\text{Mass of hydrogen}}{\text{Total mass of compound}}\times 100=\frac{1}{1+19}\times 100=5\%$

Therefore, the mass of hydrogen in the compound that is formed are, 5 %