Calculate the molar mass of octane.
The Correct Answer and Explanation is:
114.2 g/mol
To calculate the molar mass of octane, we first need to determine its molecular formula from the given condensed structural formula, CH₃(CH₂)₆CH₃, and then sum the atomic masses of all the atoms in the molecule.
First, let’s find the total number of carbon (C) and hydrogen (H) atoms. The formula shows one initial methyl group (CH₃), six repeating methylene groups (CH₂), and one final methyl group (CH₃).
- Carbon (C) atoms: There is 1 carbon in the first CH₃, 6 carbons in the (CH₂)₆ part, and 1 carbon in the last CH₃. The total number of carbon atoms is 1 + 6 + 1 = 8.
- Hydrogen (H) atoms: There are 3 hydrogens in the first CH₃, 12 hydrogens in the (CH₂)₆ part (6 groups × 2 hydrogens each), and 3 hydrogens in the last CH₃. The total number of hydrogen atoms is 3 + 12 + 3 = 18.
So, the molecular formula for octane is C₈H₁₈.
Next, we use the standard atomic masses for carbon and hydrogen, which can be found on the periodic table.
- The atomic mass of Carbon (C) is approximately 12.011 g/mol .
- The atomic mass of Hydrogen (H) is approximately 1.008 g/mol .
Now, we calculate the molar mass by multiplying the count of each atom by its respective atomic mass and adding the results together.
- Mass from Carbon = 8 atoms × 12.011 g/mol = 96.088 g/mol
- Mass from Hydrogen = 18 atoms × 1.008 g/mol = 18.144 g/mol
The total molar mass of octane is the sum of these values:
Molar Mass = 96.088 g/mol + 18.144 g/mol = 114.232 g/mol .
Finally, the question requires the answer to be rounded to one decimal place. The calculated value is 114.232. Since the second decimal digit (3) is less than 5, we round down, keeping the first decimal digit as it is.
