Molar mass Transitional Reasoning Practice

Questions

1. 1.

   A chemistry student heats a 7.35 g sample of hydrated calcium chloride, $\text{CaCl}_2 \cdot n\text{H}_2\text{O}$, until all water of crystallization is driven off, leaving 5.55 g of anhydrous $\text{CaCl}_2$. Given that the molar mass of anhydrous $\text{CaCl}_2$ is 111.0 g/mol and the molar mass of water is 18.0 g/mol, what is the molar mass of the hydrated salt?

   • A) 129.0 g/mol
   • B) 73.5 g/mol
   • C) 147.0 g/mol
   • D) 165.0 g/mol
2. 2.

   A materials scientist heats a 3.60 g sample of an unknown metal M in excess nitrogen gas until it is completely converted into 5.00 g of the pure nitride compound $\text{M}_3\text{N}_2$. Given that the molar mass of nitrogen atoms is $14.0\text{ g/mol}$, what is the molar mass of metal M?

   • A) 36.0 g/mol
   • B) 24.0 g/mol
   • C) 54.0 g/mol
   • D) 48.0 g/mol
3. 3.

   A biomedical researcher isolates a purified sample of an unknown antibody to determine its molar mass. A 2.40 g sample of this antibody is found to contain $3.01 \times 10^{19}$ individual molecules. Given that Avogadro's constant is $6.02 \times 10^{23}\text{ mol}^{-1}$, what is the molar mass of this antibody?

   • A) 12,000 g/mol
   • B) 24,000 g/mol
   • C) 36,000 g/mol
   • D) 48,000 g/mol
4. 4.

   A laboratory container holds an 8.00 g sample of pure methane gas ($\text{CH}_4$, molar mass = 16.0 g/mol). A second container holds a 100.0 g sample of an unknown noble gas that contains the exact same total number of atoms as the methane sample. Given that noble gases are monatomic, what is the molar mass of the unknown noble gas?

   • A) 200 g/mol
   • B) 80.0 g/mol
   • C) 50.0 g/mol
   • D) 40.0 g/mol
5. 5.

   A chemist synthesizes a pure gaseous compound containing only an unknown element X and oxygen. A 0.250 mol sample of this compound has a total mass of 11.00 g and is determined to contain 8.00 g of oxygen. Given that each molecule contains exactly one atom of element X and the molar mass of oxygen is 16.00 g/mol, what is the identity of element X?

   • A) Nitrogen
   • B) Boron
   • C) Beryllium
   • D) Carbon

Answers and step-by-step solutions appear after you finish the test.