If the empirical formula of a compound is CH2 and its molar mass is 70.0, then what is its molecular formula?
empirical mass is ... C + 2 H = 14
70 / 14 = 5 ... this is the multiplier for empirical to molar
5 (CH2) ---> C5H10
To determine the molecular formula of a compound given its empirical formula and molar mass, follow these steps:
1. Calculate the empirical formula mass:
- The empirical formula CH2 consists of 1 carbon atom (12.01 g/mol) and 2 hydrogen atoms (1.01 g/mol each).
- Empirical formula mass = (1 × molar mass of carbon) + (2 × molar mass of hydrogen)
- Empirical formula mass = (1 × 12.01 g/mol) + (2 × 1.01 g/mol) = 14.03 g/mol
2. Calculate the number of empirical formula units in one mole of the compound (molar mass / empirical formula mass):
- Number of empirical formula units = molar mass of the compound / empirical formula mass
- Number of empirical formula units = 70.0 g/mol / 14.03 g/mol ≈ 4.99
3. Round the number of empirical formula units to get a whole number:
- Rounding 4.99 to the nearest whole number gives 5.
4. Multiply the subscripts of the empirical formula by the whole number calculated in step 3 to determine the molecular formula:
- Molecular formula = (subscript of carbon) × 5 + (subscript of hydrogen) × 5
- Molecular formula = C5H10
Therefore, the molecular formula of the compound is C5H10.