Percent Composition and Atomic Counts

This video tutorial explains how to calculate the percent composition by mass of each element in ammonium sulfate (NH4)2SO4. It begins with nitrogen, detailing the use of atomic mass and molar mass to find its percent composition. The same method is applied to hydrogen and sulfur, emphasizing the multiplication of atomic mass by the number of atoms and dividing by the compound's molar mass. Finally, the video guides viewers through calculating the percent composition for oxygen, ensuring all elements' percentages sum to approximately 100%.

What is the first step in calculating the percent composition by mass for an element in a compound?

• Find the atomic number of the element.

• Determine the molar mass of the compound.

• Calculate the number of moles of the element.

• Identify the number of atoms of the element in the compound.

How many nitrogen atoms are present in ammonium sulfate?

• 4

• 2

• 1

• 3

What is the percent composition by mass of nitrogen in ammonium sulfate?

• 24.26%

• 6.11%

• 21.20%

• 18.04%

How many hydrogen atoms are present in ammonium sulfate?

• 8

• 10

• 6

• 4

What is the percent composition by mass of hydrogen in ammonium sulfate?

• 6.11%

• 21.20%

• 18.04%

• 24.26%

What is the percent composition by mass of sulfur in ammonium sulfate?

• 21.20%

• 6.11%

• 18.04%

• 24.26%

How many oxygen atoms are present in ammonium sulfate?

• 2

• 3

• 4

• 5

What is the final step in calculating the percent composition by mass of an element?

• Divide the atomic mass by the molar mass of the compound.

• Multiply the result by 100.

• Subtract the atomic mass from the molar mass.

• Add the atomic masses of all elements.

What should the sum of all percent compositions in a compound be close to?

• 150%

• 50%

• 100%

• 75%

Who is the presenter of the video tutorial?

• Dr. B

• Dr. A

• Dr. D

• Dr. C