Molecular and Empirical Formulas

• What are molecular and empirical formulas used to represent?

  Molecular and empirical formulas represent the number and type of atoms in a substance.
• What does a displayed formula show?

  A displayed formula shows the number and type of atoms in a molecule as a picture.
• How many hydrogen atoms are in methane?

  Methane contains 4 hydrogen atoms.
• How can you derive a molecular formula from a displayed formula?

  You can derive a molecular formula by matching each carbon atom in the displayed formula to the molecular formula.
• What does the number after a bracket in a molecular formula indicate?

  The number after a bracket indicates how many times the group of atoms in the bracket is present in the molecule.
• What is the empirical formula of a compound?

  The empirical formula tells you the smallest whole number ratio of atoms in the compound.
• What is the empirical formula of ethane, given its molecular formula C₂H₆?

  The empirical formula of ethane is CH₃.
• How do you simplify the ratio of atoms in a molecular formula?

  You simplify the ratio by dividing by the largest number that goes into all the atom counts exactly.
• What is the empirical formula of glucose, given its molecular formula C₆H₁₂O₆?

  The empirical formula of glucose is CH₂O.
• How can you find the molecular formula from the empirical formula and molar mass?

  You can find the molecular formula by dividing the molar mass of the compound by the molar mass of the empirical formula.
• How do you calculate the molar mass of the empirical formula C₃H₇N?

  The molar mass is calculated as \( (3 \times 12.0) + (7 \times 1.0) + (1 \times 14.0) = 36.0 + 7.0 + 14.0 = 57.0 \) g/mol.
• If the empirical formula of a compound is C₃H₇N and its molar mass is 114 g/mol, what is its molecular formula?

  The molecular formula is C₆H₁₄N₂.
• What is the molar mass of the empirical formula C₃H₇N?

  The molar mass of C₃H₇N is 57.0 g/mol.
• What is the process to find the molecular formula from the empirical formula and molar mass?

  1. Calculate the molar mass of the empirical formula.
  2. Divide the molar mass of the compound by the molar mass of the empirical formula.
  3. Multiply each element in the empirical formula by the result from step 2.
• What are the steps to find the empirical formula from a molecular formula?

  1. Identify the number of each type of atom in the molecular formula.
  2. Divide each atom count by the largest common factor.
  3. Write the simplest whole number ratio as the empirical formula.