A particular compound in the chemistry laboratory is found to contain $7.2 \times 10^{24}$ atoms of oxygen, $56.0 \mathrm{~g}$ of nitrogen, and $4.0$ moles of hydrogen. What is its empirical formula?

A $0.7221$-g sample of a new compound has been analyzed and found to contain the following masses of elements: carbon, $0.2990 \mathrm{~g}$; hydrogen, $0.05849 \mathrm{~g}$; nitrogen, $0.2318 \mathrm{~g}$; oxygen, $0.1328 \mathrm{~g}$. Calculate the empirical formula of the compound.

Use the graph to match compounds $\mathrm{A}, \mathrm{B}, \mathrm{C}$, and $\mathrm{D}$ with the following choices: $\mathrm{NaCN}$, $\mathrm{HNO}_3, \mathrm{NH}_3, \mathrm{Ca}\left(\mathrm{NO}_3\right)_2$ A B C D

A single molecule of a particular compound has a mass of $4.65 \times 10^{-23} \mathrm{~g}$. Which of the following could be this compound?

A. $\mathrm{CO}$
B. $\mathrm{H}_2 \mathrm{O}$
C. $\mathrm{NO}_2$
D. $\mathrm{NH}_3$

A strikingly beautiful copper compound with the common name "blue vitriol" has the following elemental composition: $25.45 \% \mathrm{Cu}, 12.84 \% \mathrm{~S}, 4.036 \% \mathrm{H}$, $57.67 \% \mathrm{O}$. Determine the empirical formula of the compound.

When a $2.118-\mathrm{g}$ sample of copper is heated in an atmosphere in which the amount of oxygen present is restricted, the sample gains $0.2666 \mathrm{~g}$ of oxygen in forming a reddish-brown oxide. However, when $2.118 \mathrm{~g}$ of copper is heated in a stream of pure oxygen, the sample gains $0.5332 \mathrm{~g}$ of oxygen. Calculate the empirical formulas of the two oxides of copper.