2.2.2 Empirical and molecular formulas

• What does the empirical formula of a compound represent?

  Simplest whole number ratio
• The molecular formula of a compound represents the actual number of atoms
• Match the characteristic with the correct type of formula:

  Molecular Formula ↔️ Actual number of atoms

  Empirical Formula ↔️ Simplest whole number ratio
• The molecular formula often is a whole number multiple of the empirical formula
• What does the molecular formula of a compound represent?

  Actual number of atoms
• How does the empirical formula relate to the molecular formula?

  Simplest whole number ratio
• Steps to identify the percentage composition of a compound

  1️⃣ Determine the molecular or empirical formula

  2️⃣ Calculate the molar mass of the compound

  3️⃣ Calculate the mass of each element

  4️⃣ Determine the percentage composition
• To identify the percentage composition of a compound, you first need to determine its molecular or empirical formula
• The percentage of each element in a compound is calculated by dividing its mass by the total molar mass and multiplying by 100.
• Calculate the percentage composition of carbon in glucose (C₆H₁₂O₆)

  1️⃣ (6 × 12.01 g/mol)

  2️⃣ (180.16 g/mol)

  3️⃣ (6 × 12.01 g/mol) / (180.16 g/mol)

  4️⃣ (6 × 12.01 g/mol) / (180.16 g/mol) × 100%
• The percentage of oxygen in glucose is calculated as (6 × 16.00 g/mol) / (180.16 g/mol) × 100%.
• Match the characteristic with the correct type of composition:

  Definition ↔️ Percentage of each element

  Calculation ↔️ Multiply percentage by total mass

  Purpose ↔️ Gives the actual mass
• The empirical formula represents the simplest whole number ratio of atoms in a compound.
• What is the empirical formula of glucose (C₆H₁₂O₆)?

  CH₂O
• The molecular formula of glucose is C₆H₁₂O₆.


  True
• The empirical formula shows the simplest whole number ratio of atoms in a compound.
• What is the molecular formula of glucose?

  C₆H₁₂O₆
• The empirical formula of glucose is CH₂O


  True
• What does the molecular formula represent?

  Actual number of atoms
• Match the formula type with its relationship:

  Empirical Formula ↔️ May be the same as or a multiple of the molecular formula

  Molecular Formula ↔️ Often a whole number multiple of the empirical formula
• The empirical formula represents the actual number of atoms in a molecule.

  False
• Steps to identify the percentage composition of a compound:

  1️⃣ Determine the molecular or empirical formula

  2️⃣ Calculate the molar mass of the compound

  3️⃣ Calculate the mass of each element

  4️⃣ Calculate the percentage of each element
• To calculate the percentage of an element in a compound, you divide its mass by the molar mass and multiply by 100.


  True
• What is the percentage of carbon in glucose (C₆H₁₂O₆)?

  40.00%
• The percentage of oxygen in glucose is 53.33%.
• Mass composition refers to the mass of each element in a compound.


  True
• What is the first step to calculate the moles of each element in a compound?

  Determine the formula
• What is the mass of carbon in 100 g of glucose (C₆H₁₂O₆)?

  72.06 g
• The moles of oxygen in 100 g of glucose are 6.00 mol.
• The moles of each element are calculated by dividing the mass of the element by its atomic mass
• How many moles of carbon are present in 100 g of glucose (C₆H₁₂O₆)?

  6.00 mol
• The mole ratio for a compound with 0.25 mol C, 0.5 mol H, and 0.25 mol O is 1:2:1


  True
• The empirical formula of glucose (C₆H₁₂O₆) is CH₂O
• What does the molecular formula of a compound represent?

  Actual number of atoms
• The molecular formula of glucose is C₆H₁₂O₆, while its empirical formula is CH₂O


  True
• What is the third step in identifying the percentage composition of a compound?

  Calculate the mass of each element
• Steps to identify the percentage composition of a compound

  1️⃣ Determine the molecular or empirical formula

  2️⃣ Calculate the molar mass

  3️⃣ Calculate the mass of each element

  4️⃣ Calculate the percentage of each element
• To convert from percentage composition to mass composition, first calculate the total mass of the compound.
• The mass composition provides the absolute amounts of each element in a compound.


  True
• The atomic mass of oxygen is 16.00 g/mol.