Q3.26P - Chemistry: Molecular Nature Of Matter And Change

Question

Propane is widely used in liquid from as a fuel for barbecue grills and camp stoves. For 85.5g of propane, calculate

1. The moles of the compound;
2. The grams of carbon.

Step-by-Step Solution

Answer

1. The Moles of Propane is $\mathbf{1}\mathbf{.}\mathbf{94}\mathbf{mol}{\mathbf{C}}_{\mathbf{3}}{\mathbf{H}}_{\mathbf{8}}$.
2. The Mass of C is $\mathbf{69}\mathbf{.90}\mathbf{g}\mathbf{C}$.

Step 1: To Calculate the moles of propane.

The Mass of propane=85.5g

The molar mass of propane, ${\mathrm{C}}_3{\mathrm{H}}_8$, is calculated below.

$\begin{array}{c}{\mathrm{M}}_{\mathrm{\omega }}\mathrm{of}{\mathrm{C}}_3{\mathrm{H}}_8=3\times \left({\mathrm{M}}_{\mathrm{\omega }}\mathrm{of}\mathrm{C}\right)+8\times \left({\mathrm{M}}_{\mathrm{\omega }}\mathrm{of}\mathrm{H}\right)\\ =3\times \left(12.01\frac{\mathrm{g}}{\mathrm{mol}}\right)+8\times \left(1.01\frac{\mathrm{g}}{\mathrm{mol}}\right)\\ =44.11\frac{\mathrm{g}}{\mathrm{mol}}\end{array}$

Multiply the given mass of propane by the reciprocal of its molar mass to get the number of moles.

Moles of propane$=85.5\mathrm{g}{\mathrm{C}}_3{\mathrm{H}}_8\left(\frac{\mathrm{mol}{\mathrm{C}}_3{\mathrm{H}}_8}{44.11\mathrm{g}{\mathrm{C}}_3{\mathrm{H}}_8}\right)$

Therefore, The Moles of propane is $1.94\mathrm{mol}{\mathrm{C}}_3{\mathrm{H}}_8$.

Step 2: To Calculate the mass of C

There are 3 moles of C atoms in 1 moles of ${\mathrm{C}}_3{\mathrm{H}}_8$. The number of moles of C atoms in 85.5 g propane is 

Moles of C$=5.82\mathrm{mol}\mathrm{C}\left(\frac{3\mathrm{mol}\mathrm{C}}{1\mathrm{mol}{\mathrm{C}}_3{\mathrm{H}}_8}\right)$

Moles of C$=5.82\mathrm{mol}\mathrm{C}$

Therefore, Multiply the calculated number of moles of carbon, C, by its molar mass which is $12.01\frac{\mathrm{g}}{\mathrm{mol}}$.

Mass of C$=5.82\mathrm{mol}\mathrm{C}\left(12.01\frac{\mathrm{g}}{\mathrm{mol}}\right)$

Mass of C$=69.90\mathrm{g}\mathrm{C}.$

Therefore, The Mass of C is $69.90\mathrm{g}\mathrm{C}.$