What is the vapor pressure (in mmHg) of a solution containing 16.0 g of (3 marks) glucose (C6H12O6) in 80.0 g of methanol (CH3OH)? The vapor pressure of pure methanol at 27 °C is 140 mm Hg. If the experimentally determined vapor pressure is 128 mm Hg, account for the difference between the two values. (3 significant figures).

Question

What is the vapor pressure (in mmHg) of a solution containing 16.0 g of (3 marks) glucose (C6H12O6) in 80.0 g of methanol (CH3OH)? The vapor pressure of pure methanol at 27 °C is 140 mm Hg. If the experimentally determined vapor pressure is 128 mm Hg, account for the difference between the two values. (3 significant figures).

Answer 1

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mols glucose = grams/molar mass
mols methanol = grams/molar mass
Total mols = mols glucose + mols methanol

mole fraction methanol = nmethanol/total mols.

psoln = X_methanol*P^o_methanol

For the difference, what about interactions between solvent molecules. What about interactions between solvent and solute?

Answer 2

To calculate the vapor pressure of the solution, we need to use Raoult's law, which states that the vapor pressure of a solution is proportional to the mole fraction of the solvent in the solution.

First, calculate the moles of glucose and methanol in the solution:

Moles of glucose = mass of glucose / molar mass of glucose
Moles of glucose = 16.0 g / 180.16 g/mol (molar mass of glucose)

Moles of methanol = mass of methanol / molar mass of methanol
Moles of methanol = 80.0 g / 32.04 g/mol (molar mass of methanol)

Next, calculate the mole fractions of glucose and methanol:

Mole fraction of glucose = moles of glucose / (moles of glucose + moles of methanol)
Mole fraction of methanol = moles of methanol / (moles of glucose + moles of methanol)

Now, use Raoult's law to find the vapor pressure of the solution:

Vapor pressure of solution = mole fraction of methanol x vapor pressure of pure methanol

Finally, calculate the difference between the experimental vapor pressure and the calculated vapor pressure:

Difference = experimental vapor pressure - calculated vapor pressure

Let's plug in the values and calculate the vapor pressure and the difference:

Moles of glucose = 16.0 g / 180.16 g/mol = 0.08883 mol
Moles of methanol = 80.0 g / 32.04 g/mol = 2.494 mol

Mole fraction of glucose = 0.08883 mol / (0.08883 mol + 2.494 mol) = 0.0346
Mole fraction of methanol = 2.494 mol / (0.08883 mol + 2.494 mol) = 0.9654

Vapor pressure of solution = 0.9654 x 140 mmHg = 135.396 mmHg

Difference = 128 mmHg - 135.396 mmHg = -7.396 mmHg (rounded to 3 significant figures)

The difference between the two values is -7.396 mmHg. A negative difference indicates that the experimentally determined vapor pressure is lower than the calculated vapor pressure. Possible reasons for this difference could include impurities in the solute or solvent, non-ideal behavior of the components, or experimental error.