Percent Composition and Molar Mass

This lecture introduces the concepts of formula mass and the mole in physical science. It explains how to calculate the formula mass for both covalent and ionic compounds, using examples like ibuprofen and aluminum sulfate. The mole concept is discussed, including Avogadro's number and its application in converting between moles and grams. The lecture also covers calculating percent composition of compounds, providing examples and emphasizing the importance of accuracy in these calculations.

What is the formula mass of a molecule?

• The sum of the average atomic masses of the atoms in a molecule

• The sum of the atomic numbers of the atoms in a molecule

• The difference between the atomic masses of the atoms in a molecule

• The product of the atomic masses of the atoms in a molecule

How is the formula mass of ionic substances different from covalent substances?

• There is no difference in calculating formula mass for ionic and covalent substances

• Covalent substances have a lattice structure, so their formula mass is not a molecular mass

• Ionic substances form a lattice structure, so their formula mass is not a molecular mass

• Ionic substances have a molecular mass, while covalent substances do not

What is Avogadro's number?

• 6.02 x 10^23

• 9.81 x 10^23

• 3.14 x 10^23

• 1.67 x 10^23

What does the molar mass of a substance represent?

• The mass in grams of one mole of the substance

• The density of one mole of the substance

• The number of atoms in one mole of the substance

• The volume of one mole of the substance

How many moles are in 4.7 grams of potassium if the molar mass is 39.10 grams per mole?

• 0.47 moles

• 1.23 moles

• 0.12 moles

• 4.70 moles

If a liter of air contains 9.2 x 10^-4 moles of argon, what is the mass of argon in grams?

• 0.400 grams

• 0.004 grams

• 0.037 grams

• 0.092 grams

What is the first step in finding the percent composition of a compound?

• Calculate the total mass of the compound

• Determine the number of moles of each element

• Find the atomic mass of each element

• Divide the mass of each element by the total mass of the compound

In a compound with 7.34 grams of carbon, 1.385 grams of hydrogen, and 2.85 grams of nitrogen, what is the percent composition of carbon?

• 100%

• 23.7%

• 15.4%

• 61%

Why is it important to ensure the total percent composition of a compound is close to 100%?

• To ensure the compound is stable

• To verify the accuracy of the calculations

• To check the purity of the compound

• To confirm the compound's molecular structure

What is the formula mass of aspirin (C9H8O4)?

• 160.154 grams per mole

• 200.154 grams per mole

• 150.134 grams per mole

• 180.154 grams per mole