Empirical and Molecular Formulas

What is a molecular formula?

• A molecular formula shows the actual number of atoms of each element in a molecule of a compound.

• A molecular formula represents the ratio of different elements in a compound.

• A molecular formula indicates the physical state of a compound at room temperature.

• A molecular formula is a graphical representation of the molecular structure.

What is the empirical formula for a compound with 72.2% magnesium and 27.8% nitrogen?

• Mg2N3

• Mg3N2

• MgN

• Mg4N

What is the empirical formula for Si2F6?

• SiF2

• SiF3

• Si2F3

• SiF4

If a compound has a molecular formula of C4F8, what is its empirical formula?

• C2F4

• CF2

• C4F8

• C3F6

If the empirical formula is NH2 and the molecular mass is 32 g/mol, what is the molecular formula?

• N2H4

• NH3

• N2H2

• NH4

How do you determine the empirical formula from percent composition?

• Convert the percentages to grams, then to moles, and find the simplest whole-number ratio.

• Add the percentages together to get a total mass and divide by the number of elements.

• Multiply the percentages by the molar mass of each element to find the empirical formula.

• Use the percent composition to directly write the empirical formula without any calculations.

What is the empirical formula of a compound with 40% carbon and 60% oxygen by mass?

• CO

• C2O2

• C3O3

• C4O4

What is the relationship between empirical and molecular formulas?

• The empirical formula is a simplified version of the molecular formula, showing the ratio of elements.

• The empirical formula is always identical to the molecular formula.

• The empirical formula represents the actual number of atoms in a molecule.

• The empirical formula is used only for ionic compounds.

How many hydrogen atoms are in C18H34O3?

• 30

• 32

• 34

• 36

Given the molecular formula C6H12O6, what is the empirical formula?

• C6H12O6

• C3H6O3

• CH2O

• C2H4O2