Percent composition Transitional Reasoning Practice

Questions

1. 1.

   A biochemist evaluates two organic metabolites, lactic acid ($\text{C}_3\text{H}_6\text{O}_3$) and glucose ($\text{C}_6\text{H}_{12}\text{O}_6$), for their elemental composition during a cell-culture formulation study. Given atomic molar masses of $\text{C} = 12\text{ g/mol}$, $\text{H} = 1\text{ g/mol}$, and $\text{O} = 16\text{ g/mol}$, what is the theoretical percent by mass of carbon in glucose, and how does it compare to the percent by mass of carbon in lactic acid?

   • A) 33.3%, and it is lower than that of lactic acid
   • B) 40.0%, and it is greater than that of lactic acid
   • C) 40.0%, and it is equal to that of lactic acid
   • D) 50.0%, and it is equal to that of lactic acid
2. 2.

   A materials chemist analyzes a synthetic copper oxide catalyst to verify whether the product formed as copper(I) oxide ($\text{Cu}_2\text{O}$) or copper(II) oxide ($\text{CuO}$). In the laboratory, complete thermal reduction of a 20.0 g sample of the pure oxide produces exactly 16.0 g of elemental copper. Taking the atomic molar masses as $\text{Cu} = 64\text{ g/mol}$ and $\text{O} = 16\text{ g/mol}$, what is the percent by mass of copper in the analyzed sample, and which oxide does this confirm?

   • A) 88.9% copper, confirming that the catalyst is copper(I) oxide ($\text{Cu}_2\text{O}$)
   • B) 80.0% copper, confirming that the catalyst is copper(II) oxide ($\text{CuO}$)
   • C) 80.0% copper, confirming that the catalyst is copper(I) oxide ($\text{Cu}_2\text{O}$)
   • D) 20.0% copper, confirming that the catalyst is copper(II) oxide ($\text{CuO}$)
3. 3.

   An extraction metallurgist compares pure samples of rutile ($\text{TiO}_2$) and ilmenite ($\text{FeTiO}_3$) to select the more efficient mineral source for titanium production. Given atomic molar masses of $\text{Ti} = 48\text{ g/mol}$, $\text{Fe} = 56\text{ g/mol}$, and $\text{O} = 16\text{ g/mol}$, what is the theoretical percent by mass of titanium in rutile, and how does it compare to the titanium content in ilmenite?

   • A) 40.0% in rutile, which is lower than that in ilmenite
   • B) 48.0% in rutile, which is lower than that in ilmenite
   • C) 60.0% in rutile, which is higher than that in ilmenite
   • D) 75.0% in rutile, which is higher than that in ilmenite
4. 4.

   An agronomist evaluates a commercial fertilizer containing urea, $\text{CO(NH}_2)_2$, mixed with inert carriers. Taking the atomic molar masses as $\text{C} = 12\text{ g/mol}$, $\text{O} = 16\text{ g/mol}$, $\text{N} = 14\text{ g/mol}$, and $\text{H} = 1\text{ g/mol}$, the theoretical percent composition of nitrogen in pure urea must be determined. If a 75.0 kg bag contains 80.0% urea by mass, what is the theoretical percent by mass of nitrogen in pure urea and the total mass of elemental nitrogen supplied by the bag?

   • A) 23.3% and 14.0 kg
   • B) 23.3% and 17.5 kg
   • C) 46.7% and 35.0 kg
   • D) 46.7% and 28.0 kg
5. 5.

   An analyst in an industrial laboratory evaluates a high-purity iron(III) oxide, $\text{Fe}_2\text{O}_3$, sample to determine yield expectations before smelting. Taking the molar masses of iron and oxygen as 56 g/mol and 16 g/mol respectively, what is the percent composition by mass of iron in pure iron(III) oxide, and what mass of iron can be extracted from a 16.0 g sample of this compound?

   • A) 30% iron by mass and 4.8 g of iron
   • B) 35% iron by mass and 5.6 g of iron
   • C) 56% iron by mass and 8.96 g of iron
   • D) 70% iron by mass and 11.2 g of iron

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