Empirical/Molecular Formulas and Percent Composition

An empirical formula shows the...

• lowest whole number ratio of elements in a compound

• actual number of each element in a compound

• number of valence electrons in a compound

• number of protons in a compound

Which of the following is an empirical formula?

• H₂O₂

• C₆H₁₂O₆

• NO₂

• P₂O₄

For what type of compound is the molecular formula usually equal to the empirical formula?

• ionic

• covalent

What is the molecular formula of a compound with an empirical formula of CH₂ and a molar mass of 70.15 g/mol?

• C₃H₆

• C₅H₁₀

• C₂H₄

• CH₄

How many of each element are in Al₂(CO₃)₃?

• Al = 2; C = 1; O = 3

• Al = 2; C = 3; O = 9

• Al = 2; C = 1; O = 9

• Al = 2; C = 4; O = 6

Tags

NGSS.MS-PS1-1

What is the molar mass of CH₄?

• 10.0 g/mol

• 13.02 g/mol

• 16.05 g/mol

• 5.0 g/mol

What is the percent of carbon in CH₄ by mass? (HINT: use the molar mass from the last question)

• 74.8%

• 37.4%

• 25.2%

• 20.0%

What do chemists call an ionic compound that has water attached to it?

• hydronium

• hydroxide

• hydrophobic

• hydrate

Which of the following would give you the molar mass of AlCl₃ * 6 H₂O?

• 26.98 + (3 x 35.45) - (6 x 18.02)

• 26.98 + (3 x 35.45) + (6 x 18.02)

• 26.98 + 35.45 + 18.02

• 26.98 + (3 x 35.45) x (6 x 18.02)

The molar mass of CoCl₂ * 6 H₂O is 237.95 g/mol. Which of the following would give you the percent water by mass?

• [(6 x 18.02) / 237.95] x 100

• [(6 + 18.02) / 237.95] x 100

• (237.95 / 18.02) x 100

• (18.02 / 237.95) x 100