Q21P - Chemistry: Molecular Nature Of Matter And Change

Question

Galena, a mineral of lead, is a compound of the metal with sulfur. Analysis shows that a 2.34-g sample of galena contains2.03 g of lead. Calculate the mass percent of lead and sulfur in galena.

Step-by-Step Solution

Answer

Galena = Pb + S

This means Galena has a composition containing Pb and S.

The mass percent of lead = 86.8%

And the mass percent of sulfur = 13.2%

Step1. Calculation of mass of sulfur and mass fraction of lead and sulfur.

According to the question, 

Mass of Galena is 2.34g and Mass of Lead is 2.03g

Now we have to calculate the mass of Sulfur = mass of Galena – a mass of Sulfur

                                                                   = 2.34 – 2.03

                                                                   = 0.31 g

So the mass of Sulfur is 0.31g 

Now calculating the mass fraction of lead and sulfur:

Mass fraction of lead = $\frac{\mathbf{2}\mathbf{.}\mathbf{3}\mathbf{ }\mathbf{g}}{\mathbf{2}\mathbf{.}\mathbf{34}\mathbf{ }\mathbf{g}}\mathbf{=}\mathbf{0}\mathbf{.}\mathbf{868}$

Mass fraction of Sulfur = $\frac{\mathbf{0}\mathbf{.}\mathbf{31}\mathbf{g}}{\mathbf{2}\mathbf{.}\mathbf{34}\mathbf{g}}\mathbf{=}\mathbf{0}\mathbf{.}\mathbf{132}$

Step2. Calculation of mass percent of lead and sulfur.

Mass % of Pb = $\frac{\mathbf{2}\mathbf{.}\mathbf{03}\mathbf{ }\mathbf{g}}{\mathbf{2}\mathbf{.}\mathbf{34}\mathbf{ }\mathbf{g}}\mathbf{=}\mathbf{0}\mathbf{.}\mathbf{868}\mathbf{\times }\mathbf{100}\mathbf{=}\mathbf{86}\mathbf{.}\mathbf{8}\mathbf{\%}$

Mass % of Sulfur = $\frac{\mathbf{0}\mathbf{.}\mathbf{31}\mathbf{ }\mathbf{g}}{\mathbf{2}\mathbf{.}\mathbf{34}\mathbf{ }\mathbf{g}}\mathbf{=}\mathbf{0}\mathbf{.}\mathbf{132}\mathbf{\times }\mathbf{100}\mathbf{=}\mathbf{13}\mathbf{.}\mathbf{2}\mathbf{\%}$

Therefore, the Mass percent of Lead is 86.8% and the Mass percent of Sulfur is 13.2%