i asked this question earlier and thanks to dr bob i got the empirical formula. which is C6H3O2. I need help finding the molar mass to get the molecular formula.
Terephthalic acid is an important chemical used in the manufacture of polyesters and plasticizers. It contains only C, H, and O. Combustion of 19.81 mg terephthalic acid produces 41.98 mg CO2 and 6.45 mg H2O. If 0.262 mol of terephthalic acid has a mass of 43.5 g, determine the molecular formula for terphthalic acid.
What is 43.5g/.262 ?
To find the molecular formula of terephthalic acid, we need to determine its molar mass.
The given empirical formula for terephthalic acid is C6H3O2, which tells us the ratio of carbon, hydrogen, and oxygen atoms in the compound.
To find the molar mass, we need to calculate the sum of the atomic masses of all the atoms in the empirical formula. We can look up the atomic masses from the periodic table:
- Atomic mass of carbon (C) = 12.01 g/mol
- Atomic mass of hydrogen (H) = 1.01 g/mol
- Atomic mass of oxygen (O) = 16.00 g/mol
Now, let's calculate the molar mass:
Molar mass of terephthalic acid = (6 * atomic mass of carbon) + (3 * atomic mass of hydrogen) + (2 * atomic mass of oxygen)
Molar mass of C6H3O2 = (6 * 12.01 g/mol) + (3 * 1.01 g/mol) + (2 * 16.00 g/mol)
Molar mass of C6H3O2 = 72.06 g/mol + 3.03 g/mol + 32.00 g/mol
Molar mass of C6H3O2 = 107.09 g/mol
So, the molar mass of terephthalic acid is 107.09 g/mol.
To determine the molecular formula, we need to compare the molar mass of the empirical formula (C6H3O2) to the experimental molar mass given in the question.
Experimental molar mass = 43.5 g/mol
Since the experimental molar mass is less than the molar mass of the empirical formula, it means that the empirical formula is a sub-multiple of the molecular formula.
To find the molecular formula, we need to divide the experimental molar mass by the molar mass of the empirical formula:
Molecular formula ratio = Experimental molar mass / Empirical molar mass
Molecular formula ratio = 43.5 g/mol / 107.09 g/mol
Molecular formula ratio ≈ 0.406
Since we want whole numbers for the molecular formula, we need to multiply the empirical formula by a factor so that the ratio becomes close to a whole number.
In this case, we can multiply the empirical formula by 2:
2 * C6H3O2 = C12H6O4
Now, let's calculate the molar mass of the molecular formula C12H6O4:
Molar mass of C12H6O4 = (12 * atomic mass of carbon) + (6 * atomic mass of hydrogen) + (4 * atomic mass of oxygen)
Molar mass of C12H6O4 = (12 * 12.01 g/mol) + (6 * 1.01 g/mol) + (4 * 16.00 g/mol)
Molar mass of C12H6O4 = 144.12 g/mol + 6.06 g/mol + 64.00 g/mol
Molar mass of C12H6O4 = 214.18 g/mol
Therefore, the molecular formula of terephthalic acid is C12H6O4.