Percent Composition and Molar Mass

The video tutorial explains how to determine the percent composition by mass of each element in magnesium oxide (MgO) using the periodic table and a specific formula. It covers the calculation of the molar mass of magnesium and oxygen, and how to use these values to find the percent composition of each element in the compound. The tutorial also notes that rounding differences may occur depending on the periodic table used, but the total should be close to 100%.

What is the first step in determining the percent composition by mass for elements in a compound?

• Use a chemical equation.

• Guess the percentage based on experience.

• Refer to the periodic table for molar masses.

• Use a calculator to find the percentage.

What is the molar mass of magnesium used in the calculation for MgO?

• 16.00 grams per mole

• 40.31 grams per mole

• 24.31 grams per mole

• 12.01 grams per mole

How do you calculate the percent composition of magnesium in MgO?

• Add the molar mass of Mg and O together.

• Subtract the molar mass of Mg from the molar mass of MgO.

• Multiply the molar mass of Mg by the molar mass of MgO.

• Divide the molar mass of Mg by the molar mass of MgO and multiply by 100.

What is the percent composition of magnesium in MgO?

• 60.31%

• 24.31%

• 39.69%

• 50.00%

What is the molar mass of oxygen used in the calculation for MgO?

• 24.31 grams per mole

• 40.31 grams per mole

• 16.00 grams per mole

• 12.01 grams per mole

How is the percent composition of oxygen in MgO calculated?

• Add the molar mass of O and Mg together.

• Subtract the molar mass of O from the molar mass of MgO.

• Multiply the molar mass of O by the molar mass of MgO.

• Divide the molar mass of O by the molar mass of MgO and multiply by 100.

What is the percent composition of oxygen in MgO?

• 60.31%

• 39.69%

• 50.00%

• 16.00%

Why might there be slight differences in the percent composition calculations?

• Different periodic tables may round atomic masses differently.

• The calculations are always exact.

• The molar mass of compounds changes over time.

• The periodic table is updated monthly.