AP Chemistry : Stoichiometry

Study concepts, example questions & explanations for AP Chemistry

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Example Questions

Example Question #1 : Unit Conversions

A \(\displaystyle 3453 g\) sample of an unknown substance occupies a volume of \(\displaystyle 250.0 cm^3\). Find the density in \(\displaystyle \frac{g}{cm^3}\).

Possible Answers:

\(\displaystyle 13.812 \frac{g}{cm^3}\)

\(\displaystyle .07240 \frac{g}{cm^3}\)

\(\displaystyle 13.81 \frac{g}{cm^3}\)

\(\displaystyle .0724 \frac{g}{cm^3}\)

\(\displaystyle 13.8 \frac{g}{cm^3}\)

Correct answer:

\(\displaystyle 13.81 \frac{g}{cm^3}\)

Explanation:

Remember: \(\displaystyle D = \frac{m}{V}\)

Therefore to find density we must divide the given mass by the given volume.

\(\displaystyle D = \frac{3453 g}{250.0 cm^3} = 13.812 \frac{g}{cm^3}\)

However, we must remember our significant figure rules. In this case both the given values have 4 significant figures. So, our answer can only have 4 significant figures. Therefore after rounding the correct answer is \(\displaystyle 13.81 \frac{g}{cm^3}\).

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