Percent by Mass

Percent Composition by Mass

Multiple Choice

How many moles are in 75.46 g of sulfuric acid, H2SO4(aq)(gram formula mass = 98 g/mol)?

How many moles are present?

• 75.46 g

• 98 g/mol

• unknown

Multiple Choice

How many moles are in 75.46 g of sulfuric acid, H2SO4(aq)(gram formula mass = 98 g/mol)?

How much mass is present?

• 75.46 g

• 98 g/mol

• unknown

Multiple Choice

How many moles are in 75.46 g of sulfuric acid, H2SO4(aq)(gram formula mass = 98 g/mol)?

What is the gram formula mass?

• 75.46 g

• 98 g/mol

• unknown

Open Ended

How many moles are in 75.46 g of sulfuric acid, H2SO4(aq)(gram formula mass = 98 g/mol)?

Remember:

mol = mol

mass = 75.46

gfm = 98

mol = mass/gfm

Percent Composition

Percent composition is used to determine what percentage of a compound (the whole) is one specific type of element.

Percent Composition

Step 1: Determine the gram formula mass [either calculate it or list], this will be the mass of the whole.

Step 2: Determine the mass of the part, the part is the specific element that you are solving for.  Remember, it is the total mass of the element.

Step 3: Substitute the values into the formula listed on table T for % composition by mass.

Step 4: Solve.

Example 1:

What is the percent composition by mass of nitrogen in dinitrogen pentoxide, N2O5 (gram formula mass = 108 g/mol)

Multiple Choice

What is the percent composition by mass of nitrogen in the compound N2H4 (gram formula mass = 32 g/mol)?

What is the part?

• N2

• H4

Multiple Choice

What is the percent composition by mass of nitrogen in the compound N2H4 (gram formula mass = 32 g/mol)?

What is the mass of the part? Remember there are 2 nitrogen.

• 7 g

• 14 g

• 28 g

Multiple Choice

What is the percent composition by mass of nitrogen in the compound N2H4 (gram formula mass = 32 g/mol)?

What is the mass of the whole?

• 28 g

• 32 g/mol

• unknown

Example 2:

What is the percent composition by mass of nitrogen in the compound N2H4 (gram formula mass = 32 g/mol)?

Open Ended

What is the percent composition by mass of nitrogen in the compound N2H4 (gram formula mass = 32 g/mol)?

mass of part = 28

mass of the whole = 32

% comp = (mass of part/mass of whole) *100