Empirical & Molecular Formulas Practice Quiz

What is the percent composition of fluorine in CF₄?

• 20%

• 13.6%

• 16.8%

• 86.4%

Magnesium oxide can be prepared by heating magnesium metal so that it reacts with oxygen in air. If 3.16 g Mg produces 5.24 g MgO, what is the percent composition of the magnesium?

• 39.7%

• 60.3%

• 34.2%

• 65.7%

Tags

NGSS.HS-PS1-7

The formula for methanol is CH₃OH (molar mass = 32.05 g/mol). Calculate the percent composition of hydrogen in methanol.

• 67%

• 11%

• 13%

• 35%

What should be the first step in calculating the percent composition of a compound?

• Use the percent composition formula

• Identify if the compound is ionic or covalent

• Multiply the answer by 100

• Calculate the molar mass of the compound

Ashley is asked to determine the percent composition of hydrogen in methane (CH₄). She calculates the molar mass of methane and gets 16.05 g/mol. Then she divides the mass of hydrogen (1.01 g/mol) by the molar mass of methane and multiplies by 100. When she shows her answer to her teacher, he tells her that this answer is wrong. What has Ashley done wrong?

• She forgot to multiply the mass of hydrogen by the number of hydrogens in the formula

• She calculated the percent composition of carbon instead of the percent composition of hydrogen

• She calculated the molar mass wrong

• Her teacher was mistaken and Ashley was correct

To find the percent composition of hydrogen in C₃H₈ (molar mass = 44.11 g/mol), you would need to use which of the following formulas?

• (1.01/44.11) x 100

• (44.11/1.01) x 100

• (8x 1.01/44.11) x 100

• There is not enough information

A compound is formed when 9.03 g sodium (Na) combines completely with 3.48 g chlorine (Cl). To find the percent composition of chlorine, you would need to which of the following first?

• Divide the mass of chlorine by the molar mass of the compound

• Find the total mass of the compound by adding the mass of sodium and mass of chlorine

• Multiply the mass of chlorine by 100

• Subtract the mass of chlorine from the mass of sodium

When a 10.0 g sample of MgO is decomposed into its element by heating, 9.3 g Mg is obtained. What is the percent composition of Mg?

• 7%

• 108%

• 93%

• 6.6%

Tags

NGSS.HS-PS1-7

The percent composition of a compound is

• The molar mass of the compound

• The molar mass of the compound divided by the mass of each element in the compound

• The mass of each element in the compound divided by the molar mass of the compound

• More than one of these is correct

To find the percent composition of iron in FeCl₂ (molar mass = 126.75 g/mol), which of the following would you use?

• (2 x 35.45/126.75) x 100

• (55.85/126.75) x 100

• (126.75/55.85) x 100

• (2 x 55.85/126.75) x 100