AP Chemistry 1.4 A Explain the Quantitative Relationship Between the Elemental Composition By Mass and the Composition of Questions

Calculate the percent by mass of Fe in the original sample of powdered Fe(s) with the inert impurity.

$$\begin{gathered} 0.09431 \mathrm{~mol} \mathrm{Fe} \times \frac{55.85 \mathrm{~g} \mathrm{Fe}}{1 \mathrm{~mol}}=5.267 \mathrm{~g} \mathrm{Fe} \frac{5.267 \mathrm{~g} \mathrm{Fe}}{6.724 \mathrm{~g} \text { sample }} \times 100=78.33 \% \end{gathered}$$

1 point is earned for correct calculation of the
mass percent based on the answer to part (g).

The calculated mass percent of Fe would be lower than the actual mass percent of Fe.

A sample that contains any FeO (rather than $\mathrm{Fe}_{2} \mathrm{O}_{3}$ ) will have a higher actual mass percent of Fe than a completely oxidized sample would have. Therefore, when the moles of Fe are calculated (assuming all the mass of the sample is $\mathrm{Fe}_{2} \mathrm{O}_{3}$ ) the calculated number of moles of Fe, and hence the calculated mass percent of Fe, will be lower.

1 point is earned for the correct answer and a valid explanation.

Sulfur atom = Carbon atom = Oxygen atom =

Compound

Molecular Structure

Boiling Point at 1 atm
(K)

$\mathrm{CS}_{2}$

COS