A sample of toluene, C7H8 has a mass of 74.5 g. How many moles of benzene does it contain? How many molecules does the sample contain? How many carbon atoms does it contain?
Look at your post under Sam. These are worked almost the same way but if you don't understand please show what you know and tell me exactly what you don't understand about the question. As for mols of benzene, the answer is none although your teacher may count that wrong. It's a poorly worded question in my opinion.
I don't understand.. under Sam
I answered under Sam. Re-post with a follow up if the "mole" isn't clear.
To determine the number of moles of benzene in the sample, we first need to find the molar mass of toluene. The molar mass is the sum of the atomic masses of all the atoms in a molecule.
The molar mass of carbon (C) is approximately 12.01 g/mol, and the molar mass of hydrogen (H) is approximately 1.01 g/mol.
To calculate the molar mass of toluene (C7H8), we multiply the molar mass of carbon by 7 and add it to the molar mass of hydrogen multiplied by 8:
(12.01 g/mol x 7) + (1.01 g/mol x 8) = 91.14 g/mol
Now we can calculate the number of moles of toluene:
Number of moles = Mass of sample / Molar mass
= 74.5 g / 91.14 g/mol
≈ 0.82 moles
Since the molecular formula of toluene is C7H8, which means it has one benzene ring, there are 0.82 moles of benzene in the sample.
To determine the number of molecules in the sample, we can use Avogadro's number, which is approximately 6.022 x 10^23 molecules/mol.
Number of molecules = Number of moles x Avogadro's number
≈ 0.82 moles x 6.022 x 10^23 molecules/mol
≈ 4.95 x 10^23 molecules
Therefore, the sample contains approximately 4.95 x 10^23 molecules.
Each benzene molecule contains 6 carbon atoms. Since we have 0.82 moles of benzene, we can calculate the number of carbon atoms in the sample:
Number of carbon atoms = Number of moles x Number of carbon atoms per molecule
= 0.82 moles x 6 carbon atoms/molecule
= 4.92 carbon atoms
However, it is not possible to have a fraction of a carbon atom. Therefore, the sample contains 5 carbon atoms.