5.1.1 Empirical and Molecular Formulae

• What is the empirical formula of a compound?

  Simplest whole number ratio
• The empirical formula indicates the total number of atoms in a molecule.

  False
• Match the features with their correct formula type:

  Simplest whole number ratio of atoms ↔️ Empirical formula

  Actual number and arrangement of atoms ↔️ Molecular formula
• What does the molecular formula represent?

  Actual number of atoms
• The molecular formula shows the total count and arrangement of atoms in a molecule.
• Steps to determine the empirical formula from percentage composition

  1️⃣ Convert percentages to grams

  2️⃣ Convert grams to moles

  3️⃣ Calculate mole ratio

  4️⃣ Simplify to whole numbers

  5️⃣ Write the empirical formula
• What assumption is made when converting percentages to grams in the empirical formula calculation?

  100g of the compound
• To convert grams to moles, use the formula: $Moles =$$\frac{Mass \ \in \ grams}{Molar \ mass}$, where the denominator is the molar mass.
• If the mole ratios are already whole numbers, no simplification is needed.
• What is the empirical formula of a compound containing 40% carbon, 6.67% hydrogen, and 53.33% oxygen?

  $CH_{2}O$
• To calculate the mole ratio, you divide each mole value by the smallest
• If the mole ratios are not whole numbers, they must be multiplied by a common factor to simplify them.
• How are the whole number mole ratios used in the empirical formula?

  As subscripts
• Steps to determine the empirical formula from percentage composition

  1️⃣ Convert percentages to grams

  2️⃣ Convert grams to moles

  3️⃣ Calculate mole ratio

  4️⃣ Simplify to whole numbers

  5️⃣ Write the empirical formula
• What does the empirical formula of a compound represent?

  Simplest whole number ratio
• The molecular formula shows the actual number and arrangement of atoms
• The empirical formula is used to understand molecular structure and properties.

  False
• What does the molecular formula of a compound represent?

  Actual number of atoms
• The molecular formula provides information about both composition and structure
• Steps to determine the empirical formula from percentage composition

  1️⃣ Convert percentages to grams

  2️⃣ Convert grams to moles

  3️⃣ Calculate mole ratio

  4️⃣ Simplify to whole numbers

  5️⃣ Write the empirical formula
• What are the steps to determine the molecular formula from the empirical formula and molar mass?

  Calculate empirical formula molar mass ||| Find the multiplication factor ||| Multiply empirical formula subscripts
• The molecular formula shows the actual number of atoms of each element
• The empirical formula shows the simplest whole number ratio of atoms in a molecule.
• Steps to determine the molecular formula from the empirical formula and molar mass

  1️⃣ Calculate empirical formula molar mass

  2️⃣ Find the multiplication factor

  3️⃣ Multiply empirical formula subscripts by the factor
• Match the steps with their corresponding action:

  Convert percentages to moles ↔️ Empirical Formula

  Calculate molar mass of empirical formula ↔️ Molecular Formula
• For glucose, the empirical formula is CH_{2}O
• The molar mass of CH_{2}O is approximately 30 g/mol.
• Steps to calculate the empirical formula from percentage composition

  1️⃣ Assume 100g of compound

  2️⃣ Convert mass to moles

  3️⃣ Find the mole ratio

  4️⃣ Simplify ratios to whole numbers

  5️⃣ Write the empirical formula
• To find the multiplication factor, divide the molar mass of the molecular formula by the molar mass of the empirical formula.
• The molar mass of a compound is the sum of the atomic masses of its elements multiplied by their subscripts.
• What is the mole ratio of carbon to hydrogen to oxygen in the example compound?

  1:2:1
• Match the step with the correct formula:

  Mass to moles ↔️ $Moles =$$\frac{Mass}{Molar \ mass}$

  Determine multiplication factor ↔️ $Factor =$$\frac{Molar \ mass \ of \ molecular \ formula}{Molar \ mass \ of \ empirical \ formula}$
• What is the multiplication factor for the example compound to determine its molecular formula?

  6
• The molecular formula for the example compound is C_{6}H_{12}O_{6}