Hexane is a hydrocarbon (a molecule containing only carbon and hydrogen) with a molecular weight of 86.18 g/mol,
a density of 0.660 g/mL, and a boiling point of 69C.
Pentanol is an alcohol (a hydrocarbon with a "OH" group attached to one of its carbons) with a molecular weight of
88.15 g/mol, a density of 0.814 g/mL, and a boiling point of 137C.
Calculate the volumes if 4.00 moles of each chemical is present.
Hexane: mL
Pentanol: mL
Think about this for the experiment you will perform in lab this week: You calculated the above volumes from the same number of molecules (moles). Why did you end up with two different volumes? The answer goes beyond the differences in the formula weights and densities.
mass = volume x density
mols = grams/molar mass. You know mols and molar mass; calculate grams, then substitute grams (for mass) in volume x density. You know density. Calculate volume.
I will leave the thought part to you. Think about it.
To calculate the volumes of 4.00 moles of hexane and pentanol, you need to use their respective densities. Here's how you can do it:
1. Calculate the volume of hexane:
To calculate the volume of hexane, you can use the formula:
Volume = Mass / Density
Given:
Molecular weight of hexane = 86.18 g/mol
Density of hexane = 0.660 g/mL
First, calculate the mass of hexane:
Mass of hexane = Number of moles × Molecular weight
Mass of hexane = 4.00 moles × 86.18 g/mol
Next, calculate the volume of hexane:
Volume of hexane = Mass of hexane / Density
Volume of hexane = (4.00 moles × 86.18 g/mol) / 0.660 g/mL
This will give you the volume of 4.00 moles of hexane in milliliters (mL).
2. Calculate the volume of pentanol:
To calculate the volume of pentanol, use the same formula:
Volume = Mass / Density
Given:
Molecular weight of pentanol = 88.15 g/mol
Density of pentanol = 0.814 g/mL
Calculate the mass of pentanol:
Mass of pentanol = Number of moles × Molecular weight
Mass of pentanol = 4.00 moles × 88.15 g/mol
Next, calculate the volume of pentanol:
Volume of pentanol = Mass of pentanol / Density
Volume of pentanol = (4.00 moles × 88.15 g/mol) / 0.814 g/mL
This will give you the volume of 4.00 moles of pentanol in milliliters (mL).
Now, let's address the question of why you ended up with two different volumes for the same number of moles. The difference in volume is not solely due to the differences in molecular weights and densities.
One key factor that affects the volume of a substance is the intermolecular forces between its molecules. Hexane is a hydrocarbon, meaning its molecules primarily have only weak Van der Waals forces between them. As a result, the molecules can more easily move past one another, leading to a higher volume for the same number of moles.
On the other hand, pentanol is an alcohol, which means it has a polar "OH" group attached to one of its carbons. This polar group leads to stronger intermolecular hydrogen bonding between the molecules. These hydrogen bonds restrict the movement of molecules and make pentanol more compact, resulting in a lower volume for the same number of moles compared to hexane.
Therefore, the differences in intermolecular forces, specifically the hydrogen bonding in pentanol, contribute to the different volumes observed.