9.1 Percent Composition & Empirical Formulas

Multiple Choice

The law of definite proportions states that a given chemical compound always contains the same _ in the exact same _ by mass.

• elements, compounds

• elements, molecules

• elements, proportions

• proportions, elements

Multiple Choice

When a 14.2-g sample of mercury(II) oxide is decomposed into its elements by heating, 13.2 g Hg is obtained. What is the percent composition of O?

• 7%

• 10%

• 12.4%

• 13.3%

Multiple Choice

What is the percent by mass of nitrogen in NH₃?

• 21.4%

• 82.4%

• 14.4%

• 2.4%

Multiple Choice

What is the percent by mass of nitrogen in NH₄NO₃?

• 21.4%

• 82.4%

• 35.0%

• 22.3%

Multiple Choice

Carbon monoxide, a deadly gas, has a chemical formula of CO (one carbon atom with one oxygen atom). If you look at the total atomic mass of CO, does carbon or oxygen make up more of the mass?

• carbon

• oxygen

• they are exactly the same

• it is impossible to tell

Multiple Choice

Lithium phosphide (three lithium atoms with one phosphorus atom) has a chemical formula of Li₃P. If you look at the total atomic mass of Li₃P, does lithium or phosphorus make up more of the mass?

• lithium

• phosphorus

• they are exactly the same

• it is impossible to tell

Multiple Choice

Calculate the grams of nitrogen in 125 g of NH₃

• 200 g

• 103 g

• 14.01 g

• 78 g

Multiple Choice

Calculate the grams of nitrogen in 125 g of NH₄NO₃

• 43.8 g

• 103 g

• 14.01 g

• 78.9 g

Multiple Choice

A compound consists of 72.2% magnesium(Mg) and 27.8% nitrogen(N) by mass. What is the empirical formula?

• Mg₄N₃

• MgN₂

• Mg₃N₂ 

• MgN

Multiple Choice

You are given the following percentages: 40.05% S and 59.95% O. Find the empirical formula for these elements.

• SO

• SO2

• SO3

• SO4

Multiple Choice

What is the molecular formula if the empirical formula is CH₂O and the molecular molar mass is 180.18?

• CH₂O

• C₂H₄O₂

• C₄H₈O₄

• C₆H₁₂O₆

Multiple Choice

What is the molecular formula for a compound with the empirical formula: K₂SO₄ and a molecular mass of 696g.

• K₂SO₄ 

• K₈SO₁₆

• K₈S₄O₈ 

• K₈S₄O₁₆