Ch-8 Practice Quiz

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

• Mg₄N₃
• MgN₂
• Mg₃N₂ 
• MgN

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

• CH₂O
• C₂H₄O₂
• C₄H₈O₄
• C₆H₁₂O₆

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

•  NaPO2
• Na2PO3
• Na3PO4
• NaPO4

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

• K₂SO₄ 
• K₈SO₁₆
• K₈S₄O₈ 
• K₈S₄O₁₆ 

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

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

• NaPO₂
• Na₂PO₃
• Na₃PO₄
• NaPO₄

Which one is an empirical formula?

• H₂O₂
• C₂H₆O₁₂
• CaCl₂
• N₂O₈

Answer explanation

An empirical formula is the lowest whole number ratio. Which one of the formula was the most reduced/ simplified version?

The Empirical Formula for a substance is CF₂. The Molecular formula mass is 200. g/mol. What is the Molecular formula?

• C₄F₈
• C₄F
• CF₈
• C₂F₄

Answer explanation

Here you are given 2 pieces of information:

1) the empirical formula.

2) the mass of the molecular formula.

To see if your empirical = molecular, you need to calculate the molar mass of the empirical formula!

If this mass is smaller than the mass the problem gives you, take the BIGGER MASS and divide by the smaller one! This tells you what you need to multiply your current formula by.

How many Carbons "C" are in C₁₈H₃₄O₃

• 18

• 34

• 3

• 37

which one defines percent composition?

• the percent by mass of each element in a compound

• when elements join together

• when water dries up

• elements split