What is the accepted molecular weight of the substance benzoic acid (C6H5COOH)? Use the molecular formula to calculate the mass.
The Correct Answer and Explanation is:
Correct Answer:
The accepted molecular weight (molar mass) of benzoic acid (C₆H₅COOH) is 122.12 g/mol.
Explanation:
To calculate the molecular weight of benzoic acid, we use its molecular formula: C₆H₅COOH, which can also be written as C₇H₆O₂. This formula tells us that benzoic acid contains:
- 7 carbon (C) atoms
- 6 hydrogen (H) atoms
- 2 oxygen (O) atoms
Now, we calculate the molecular weight using the atomic masses of each element:
- Carbon (C): 12.01 g/mol
- Hydrogen (H): 1.008 g/mol
- Oxygen (O): 16.00 g/mol
Step-by-step calculation:
- 7 carbon atoms × 12.01 g/mol = 84.07 g/mol
- 6 hydrogen atoms × 1.008 g/mol = 6.048 g/mol
- 2 oxygen atoms × 16.00 g/mol = 32.00 g/mol
Now, add all the contributions together:
84.07 + 6.048 + 32.00 = 122.118 g/mol
When rounded to two decimal places, the molecular weight is 122.12 g/mol.
Importance of Molecular Weight:
Molecular weight is crucial in chemistry for converting between grams and moles, which is essential for stoichiometric calculations. In experiments involving freezing point depression, boiling point elevation, or determining colligative properties, accurate molar masses are needed for correct interpretations.
Benzoic acid is often used in physical chemistry experiments due to its well-defined molecular mass and stability. Its accurate molecular weight helps predict behaviors like solubility, reaction stoichiometry, and thermodynamic properties in various solvents.
Thus, using the molecular formula and atomic masses from the periodic table, the accepted molecular weight of benzoic acid is calculated to be 122.12 g/mol.
