Understanding Percent Composition by Mass

What is the primary reason we cannot say water is ⅓ oxygen and ⅔ hydrogen by mass?

• Because water is made of molecules.

• Because water is a liquid.

• Because water is a compound.

• Because hydrogen and oxygen atoms have different atomic masses.

How do you calculate the percent composition by mass of an element in a compound?

• Add the atomic masses of all elements and divide by the number of elements.

• Divide the number of atoms by the total number of atoms.

• Divide the mass of the element by the total molar mass and multiply by 100%.

• Multiply the atomic number by the total mass.

What is the percent composition by mass of hydrogen in water?

• 11.19%

• 50%

• 88.81%

• 33.33%

What is the molecular formula of glucose?

• C6H12O6

• C12H22O11

• C6H6

• H2O

How many types of atoms are present in a glucose molecule?

• Three

• Four

• Two

• Five

What is the molar mass of glucose?

• 100 g/mol

• 180.156 g/mol

• 18.015 g/mol

• 342.3 g/mol

How do you find the molar mass of a compound like glucose?

• By adding the atomic numbers of all atoms.

• By subtracting the mass of hydrogen from the total mass.

• By dividing the total mass by the number of atoms.

• By multiplying the number of atoms by their atomic masses and summing them up.

What is the percent composition by mass of carbon in glucose?

• 20.0%

• 53.3%

• 6.7%

• 40.0%

What is the percent composition by mass of hydrogen in glucose?

• 53.3%

• 10.0%

• 40.0%

• 6.7%

What is the percent composition by mass of oxygen in glucose?

• 40.0%

• 6.7%

• 30.0%

• 53.3%