Calculating Mass Percent (3.3.7)

Question 1

• The percentage of a given component in a compound is the mass percent of that component.

Answer 1

• The percentage of a given component in a compound is the mass percent of that component.

Question 2

• The sum of the mass percentages of the components of a compound must equal 100%.

Answer 2

• The sum of the mass percentages of the components of a compound must equal 100%.

Question 3

• Mass percent can be used to determine a compound’s empirical formula, but not its molecular formula.

Answer 3

• Mass percent can be used to determine a compound’s empirical formula, but not its molecular formula.

Question 4

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%.

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.

Answer 4

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%.

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.