Empirical & Molecular Formulas Practice Quiz

The smallest whole-number ratio of atoms of each element, combined in the simplest unit of a chemical compound is known as a(n)

• Formula unit

• Empirical formula

• Molecule

• Molecular formula

Salicylic acid is a medication used most commonly to help remove the outer layer of the skin. If the compound contains 60.86% C, 4.39% H and 34.75% O, what is the empirical formula?

• C₇H₆O₃

• C₂H₂O

• C₆H₆O

• C₃H₂O₂

The empirical formula for a compound is CO₂. The molecular weight is 132.0 g/mol. What is the molecular formula?

• C₃O₆

• CO₂

• C₂O₆

• C₃O₄

What is the molecular formula for the compound with an empirical formula of OH (molar mass = 17.01 g/mol) and a molar mass of 85.05 g/mol?

• O₅H₅

• O₄H₄

• OH₅

• OH₄

Dwayne is asked to find the empirical formula of a compound that contains 30.4% nitrogen and 69.6% oxygen. What is the first step he should do?

• Multiply each number by 2

• Convert the moles into number of atoms of each element

• Round the number of each moles to either a half or whole number

• Change the percentages into grams of mass by assuming 100 grams of the compound

Which of the following would be considered a molecular formula?

• NO₃

• NO₂

• N₂O₃

• N₂O₄

Tags

NGSS.MS-PS1-1

What is the empirical formula for ethane C₂H₆?

• CH₃

• C₂H₂

• C₃H₃

• C₂H₆

The molecular formula for a compound shows the symbols of the elements with subscripts indicating the

• Actual numbers of atoms in a molecule

• Number of moles of the compound in 100 g

• Smallest whole-number ratio of the atoms

• Atomic masses of each element

Maria is asked to find the empirical formula for a compound that contains 35.98% aluminum and 64.02% sulfur by mass. She converts these percentages into mass by assuming 100 grams of compound. Then she converts the masses to moles by dividing by the atomic mass of each element. Then she rounds to the nearest half or whole number. When she shows her teacher, Maria is told she has the incorrect answer. What has Maria done wrong?

• She didn’t need to multiply by 2.

• She forgot to divide by the smallest number of moles before rounding.

• She needed to multiply by the atomic mass of each element, instead of dividing.

• She did too much work; she just needed to use the percentages to get a formula of Al₃₆S₆₄.

What information is needed to determine the molecular formula of a compound?

• Empirical formula only

• Molar mass of the compound only

• Empirical formula and molar mass of the compound

• None of these answers is correct