Molecular and Empirical Formulas

The video tutorial explains the difference between empirical and molecular formulas. It provides a step-by-step guide to calculating empirical formulas, including finding percent composition, converting to moles, and adjusting to whole numbers. An example is given using nitrogen and oxygen. The tutorial also covers how to find molecular formulas by using the empirical formula and molecular mass, with a detailed example using a compound with an empirical formula of CH2.

What is the primary difference between an empirical formula and a molecular formula?

• Empirical formula shows the smallest whole number ratio of atoms.

• Empirical formula shows the actual number of atoms in a compound.

• Molecular formula is always simpler than the empirical formula.

• Molecular formula shows the smallest whole number ratio of atoms.

Which of the following is the first step in determining an empirical formula?

• Find the molecular formula mass.

• Find the percent composition of each element.

• Convert moles to grams.

• Multiply by a number to get whole numbers.

When converting percent composition to moles, what sample size is typically assumed?

• 10 grams

• 1 gram

• 50 grams

• 100 grams

In the example problem, what is the empirical formula for a compound with 25.9% nitrogen and 74.1% oxygen?

• NO

• N2O

• NO2.5

• N2O5

What is the purpose of dividing the moles of each element by the smallest number of moles?

• To simplify the ratio to the smallest whole numbers.

• To find the molecular formula.

• To calculate the molar mass.

• To convert moles to grams.

What is the first step in finding the molecular formula?

• Calculate the molecular formula mass.

• Multiply the subscripts by a number.

• Find the empirical formula.

• Divide the molecular formula mass by the empirical formula mass.

How do you find the empirical formula mass?

• By adding the atomic masses of all atoms in the empirical formula.

• By dividing the molecular formula mass by the empirical formula mass.

• By multiplying the subscripts by the atomic masses.

• By adding the atomic masses of all atoms in the molecular formula.

In the example problem, what is the molecular formula if the empirical formula is CH2 and the molecular formula mass is 42.10 g/mol?

• C2H4

• C6H12

• CH2

• C3H6

What is the final step in determining the molecular formula?

• Find the empirical formula.

• Calculate the empirical formula mass.

• Multiply the subscripts of the empirical formula by a number.

• Divide the molecular formula mass by the empirical formula mass.

What does the number 'N' represent in the molecular formula calculation?

• The number of atoms in the molecular formula.

• The ratio of molecular formula mass to empirical formula mass.

• The atomic number of the element.

• The number of moles of the compound.