empirical and molecular formula

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

• Mg₄N₃
• MgN₂
• Mg₃N₂ 
• MgN

Empirical Formula = CF₂

Molecular formula mass = 192 g/mol

Molecular Formula = ?

• C₄F₈

• C₈F₄

• C₃F₆

• C₂F₄

The empirical formula of a substance is CH₂O. The molar mass is 180g/mol. What is the molecular formula?

• CH₂O

• C₃H₆O₃

• C₆H₁₂O₆

• C₁₂H₆O₁₂

What is the empirical formula if you have 81.82% carbon and 18.18% hydrogen?

• C3H8
• CH4
• C2H2
• C4H10

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

• SO
• SO2
• SO3
• SO4

Given the following: 42.07% Na, 18.89% P, and 39.04% O, determine the empirical formula.

•  NaPO2
• Na2PO3
• Na3PO4
• NaPO4

Glycerol has a molar mass of 92.09g/mol. Its percent composition is: 39.12% C, 8.75% H, and 51.12% O. What is the molecular formula for glycerol?

• C₂H₃O₂
• CH₂O
• C₂H₄O₂
• C₃H₈O₃

Whats the empirical formula of a molecule containing 18.7% of Lithium, 16.3% of Carbon and 65.0% of oxygen?

• CO₂Li₃
• Li₂CO₃
• Li₃CO₂
• LiCO₅

A sample contains 36.95 g of mercury (Hg) and 13.05 g of chlorine (Cl). What is the empirical formula for this compound?

• HgCl₂

• Hg₃Cl

• Hg₁₇Cl₃₆

• HgCl

Answer explanation

When you are given g and asked for the formula, you need moles!

1) use the molar masses from the Per. Tab. to convert grams -> moles.

2) if your moles are not whole numbers, you should either double all of the answers (if one of them ends in 0.5) OR divide all of the answers by the smallest answer.

** Remember, you are looking for whole number mole ratios to make a formula!

Phenyl magnesium bromide is used as a reagent in organic synthesis. Determine its molecular formula if its molar mass is 181.31 g/mol and it contains 39.75% C, 2.78% H, 13.41% Mg, and 44.07% Br (these are in the correct order).

• C₁₂H₁₀Mg₂Br₂

• CHMgBr

• C₆H₅MgBr

• C₃H_2.5MgBr