3.3.7 Calculating Mass Percent

Question 1

Calculating Mass Percent

Answer 1

• The percentage of a given component in a compound is the mass percent of that component.
• The sum of the mass percentages of the components of a compound must equal 100%.
• Mass percent can be used to determine a compound’s empirical formula, but not its molecular formula.

Question 2

note

Answer 2

• To determine the mass percent of fluorine in C11H3F2N3, first find the molar mass of each of the components. The molar mass of each element is given in grams in the periodic table.
• Next, determine the mass of one mole of the compound by substituting the molar masses into the chemical formula and calculating the sum.
• Now that you have the value for the mass of one mole of C11H3F2N3, you can use that to determine the mass percent of each of the elements that comprise the compound. Simply divide the mass of that element in one mole by the total mass of one mole and multiply by 100 to get the mass percentage of that element. The same can be done for each component element.
• It is useful to double-check your calculations by summing the mass percents of all of the components. It should always be very close to 100%.

Question 3

note 2

Answer 3

• Note that the two compounds at left, ethylene and cyclobutane, have two distinct, molecular formulas. The formula for ethylene is C4H8, and the formula for cyclobutane is C4H8.
• If you determine the mass percent of carbon in each compound, you will find that it is the same in each one. For this reason, a molecular formula cannot be determined based purely on the mass percentages of its constituents. However, mass percentages can be used to determine a compound’s empirical formula.

Question 4

What is the percent by mass of sulfur in penicillin, C14H20N2SO4?

Answer 4

10.26%

Question 5

Aspartame is a compound used as an artificial sweetener. The mass percent of oxygen in aspartame is 27.18%. There are five atoms of oxygen in aspartame. What is the molar mass of aspartame?

Answer 5

294.3 g / mol

Question 6

A 2.654 g sample of coal contains 1.8546 g of carbon. Calculate the mass percentage of carbon in the sample of coal.

Answer 6

69.88%

Question 7

Retinol (C20H30O), the dietary form of vitamin A, is a yellow fat-soluble, antioxidant vitamin important in vision and bone growth. A molecule of retinol (vitamin A) is shown below. What is the mass percent of hydrogen in retinol?

Answer 7

10.56%

Question 8

What is the percent oxygen in carbon dioxide by mass?

Answer 8

72.73%

Question 9

Which of the following compounds has the greatest mass percent of carbon?

Answer 9

ethanol, C2H5OH

Question 10

What is the mass percent of nitrogen in a compound having a molecular formula of C11H3F2N3?

Answer 10

19.53%

Question 11

A fertilizer is advertised as containing 16.44% nitrogen (per mass). How many grams nitrogen are in 8.500 kg of the fertilizer?

Answer 11

1397 g

Question 12

Clonazepam, C15H10N3ClO3 is a drug in the benzodiazepine class of pharmaceuticals. It is a highly potent anticonvulsant, amnesiac and anxiolytic. Calculate the percent by mass of each of the elements in clonazepam. Carbon makes up the largest percent by mass to this compound. Which element contributes the second largest percent by mass to this compound?

Answer 12

oxygen

Question 13

Carvone is a compound that, depending on the arrangement of its constituent atoms, can be responsible for the flavor of caraway or provide the smell for spearmint. What is the mass percent of carbon in carvone, which has a molecular formula of C10H14O?

Answer 13

None of the above