Structure 1.4—Counting particles by mass: The mole: Practice Questions

What is the amount, in moles, of \(\text{CaCO}_3\) in a \(10.0\text{ g}\) sample?
(Relative atomic masses: \(\text{Ca} = 40.0, \text{C} = 12.0, \text{O} = 16.0\))

A sample of an unknown gas occupies a volume of \(4.48 \text{ L}\) at Standard Temperature and Pressure (STP). If the mass of this sample is \(8.0 \text{ g}\), what is the molar mass of the gas?

(Assume the molar volume of an ideal gas at STP is \(22.4 \text{ L mol}^{-1}\))

A sample of an unknown hydrocarbon contains 85.6% carbon and 14.4% hydrogen by mass. If the molar mass of the hydrocarbon is approximately 56.1 g/mol, what is its molecular formula?

(Molar masses: C = 12.01 g/mol, H = 1.01 g/mol)

How many oxygen atoms are present in 147 g of sulfuric acid ($$\text{H}_2\text{SO}_4$$)?

(Molar masses: H = 1.01 g/mol, S = 32.07 g/mol, O = 16.00 g/mol; Avogadro's constant = $$6.022 \times 10^{23} \text{ mol}^{-1}$$)

a) Calculate the number of moles in $$80.1 \text{ g}$$ of calcium carbonate ($$CaCO_3$$).

b) How many oxygen atoms are present in this sample?

A compound is found to contain 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen by mass. The molar mass of the compound is approximately $$180.0 \text{ g mol}^{-1}$$.

a) Determine the empirical formula of the compound.
b) Determine the molecular formula of the compound.

(Relative atomic masses: C = 12.01, H = 1.01, O = 16.00)