Molar mass Transitional Reasoning Download PDF

Questions

1. 1.

   In an analytical laboratory, a student investigates a solid hydrate with the chemical formula $X \cdot 2\text{H}_2\text{O}$, where $X$ represents an unknown anhydrous compound. Heating a 7.80 g sample of this hydrate completely drives off all water of crystallization, leaving 6.00 g of dry compound $X$. Given that the molar mass of water ($\text{H}_2\text{O}$) is 18.0 g/mol, what is the molar mass of the anhydrous compound $X$?

   • A) 30.0 g/mol
   • B) 60.0 g/mol
   • C) 156 g/mol
   • D) 120 g/mol
2. 2.

   During the synthesis of a specialty reagent, a chemist isolates a pure liquid phosphorus halide with the molecular formula $\text{PX}_3$. Elemental analysis shows that a 40.65 g sample of this compound contains 4.65 g of phosphorus. Given that the molar mass of phosphorus is 31.0 g/mol, what is the molar mass of halogen X?

   • A) 240 g/mol
   • B) 80.0 g/mol
   • C) 90.3 g/mol
   • D) 271 g/mol
3. 3.

   A semiconductor laboratory analyzes a high-purity metal film deposited on a silicon wafer during microchip fabrication. Analytical instrumentation determines that a 0.539 g sample of this deposited metal contains exactly $3.01 \times 10^{21}$ atoms. Given that Avogadro's number is $6.02 \times 10^{23}$ atoms/mol, what is the molar mass of this metal?

   • A) 54.0 g/mol
   • B) 108 g/mol
   • C) 216 g/mol
   • D) 270 g/mol
4. 4.

   A chemist reacts a 5.40 g sample of an unknown pure metal $M$ completely with excess hydrochloric acid according to the balanced equation $2M(s) + 6\text{HCl}(aq) \rightarrow 2M\text{Cl}_3(aq) + 3\text{H}_2(g)$. The reaction proceeds to completion and produces exactly 0.300 mol of hydrogen gas. Based on this experimental outcome, what is the molar mass of metal $M$?

   • A) 18.0 g/mol
   • B) 27.0 g/mol
   • C) 12.0 g/mol
   • D) 54.0 g/mol
5. 5.

   In a laboratory investigation, a student fills two identical containers at the same temperature and pressure with equal numbers of gas molecules. Container 1 holds 4.40 g of carbon dioxide ($\text{CO}_2$, molar mass = 44.0 g/mol), while Container 2 holds 6.40 g of an unknown gaseous oxide with the molecular formula $\text{YO}_2$. Based on these experimental measurements and an atomic mass of 16.0 g/mol for oxygen, what is the molar mass of element Y?

   • A) 32.0 g/mol
   • B) 48.0 g/mol
   • C) 64.0 g/mol
   • D) 16.0 g/mol