Percent composition Transitional Reasoning Download PDF

Questions

1. 1.

   An analytical chemist conducts combustion analysis on a 4.608 g sample of an unknown liquid fuel composed solely of carbon, hydrogen, and oxygen. Complete combustion of the sample yields 8.802 g of carbon dioxide ($\text{CO}_2$) and 5.406 g of water ($\text{H}_2\text{O}$). Given the atomic molar masses of $\text{C} = 12.01\text{ g/mol}$, $\text{H} = 1.01\text{ g/mol}$, and $\text{O} = 16.00\text{ g/mol}$, what is the percent composition by mass of oxygen in the fuel sample?

   • A) 13.15%
   • B) 41.30%
   • C) 34.72%
   • D) 52.13%
2. 2.

   A metallurgical engineer evaluates pure samples of hematite ($\text{Fe}_2\text{O}_3$) and magnetite ($\text{Fe}_3\text{O}_4$) to determine which mineral provides a greater yield of iron per unit mass of pure ore. Using the atomic molar masses of $\text{Fe} = 55.85\text{ g/mol}$ and $\text{O} = 16.00\text{ g/mol}$, which mineral has the higher percent composition of iron by mass, and what are their respective theoretical values?

   • A) Hematite, because the iron content by mass is 34.97% in hematite and 24.12% in magnetite.
   • B) Magnetite, because the iron content by mass is 72.36% in magnetite and 69.94% in hematite.
   • C) Magnetite, because the iron content by mass is 42.86% in magnetite and 40.00% in hematite.
   • D) Hematite, because the iron content by mass is 72.36% in hematite and 69.94% in magnetite.
3. 3.

   A quality control chemist analyzes a dietary supplement formulated with ascorbic acid (vitamin C, $\text{C}_6\text{H}_8\text{O}_6$). Each manufactured tablet has a total mass of 500.0 mg and contains 88.0% ascorbic acid by mass, with the remainder consisting of inert binders that contain no oxygen. Given the atomic molar masses of $\text{H} = 1.01\text{ g/mol}$, $\text{C} = 12.01\text{ g/mol}$, and $\text{O} = 16.00\text{ g/mol}$, what is the theoretical percent composition by mass of oxygen in ascorbic acid, and what total mass of oxygen is present in one tablet?

   • A) 40.91% and 180.0 mg
   • B) 54.50% and 272.5 mg
   • C) 54.50% and 239.8 mg
   • D) 45.45% and 200.0 mg
4. 4.

   An agricultural testing laboratory analyzes a 50.00 g sample from a commercial fertilizer batch labeled as pure ammonium sulfate, $\text{(NH}_4\text{)}_2\text{SO}_4$. Elemental analysis reveals that this sample yields 12.00 g of elemental nitrogen. Given the molar masses $\text{N} = 14.01\text{ g/mol}$, $\text{H} = 1.01\text{ g/mol}$, $\text{S} = 32.07\text{ g/mol}$, and $\text{O} = 16.00\text{ g/mol}$, what is the relationship between the experimental nitrogen content and the theoretical percent composition of pure ammonium sulfate?

   • A) The experimental nitrogen content is 12.00%, which is less than the theoretical 21.20%, indicating that the batch is deficient in nitrogen.
   • B) The experimental nitrogen content is 24.00%, which equals the theoretical 24.00%, confirming that the sample is completely pure.
   • C) The experimental nitrogen content is 21.20%, which is less than the theoretical 28.02%, indicating that nitrogen was lost during extraction.
   • D) The experimental nitrogen content is 24.00%, which exceeds the theoretical 21.20%, indicating the presence of an impurity with a higher nitrogen mass fraction.
5. 5.

   A laboratory technician analyzes a 20.00 g sample of an unknown copper sulfide ore containing only copper and sulfur. Complete decomposition of the sample yields 15.96 g of copper and 4.04 g of sulfur. Based on the molar masses of copper (63.55 g/mol) and sulfur (32.06 g/mol), what is the mass percentage of copper in the sample, and which theoretical compound does it match?

   • A) 66.5% copper; it matches copper(II) sulfide ($\text{CuS}$).
   • B) 79.8% copper; it matches copper(I) sulfide ($\text{Cu}_2\text{S}$).
   • C) 79.8% copper; it matches copper(II) sulfide ($\text{CuS}$).
   • D) 66.5% copper; it matches copper(I) sulfide ($\text{Cu}_2\text{S}$).