Answer to Question #201293 in Chemistry for maryam

Question

A student dissolves 18. g of resveratrol ( C H ,,,) in 250 mL of a solvent with a density of 0.87 g/mL. The student notices that the volume of the solvent does not change when the resveratrol dissolves in it. Calculate the molarity and molality of the student's solution. Be sure each of your answer entries has the correct number of significant digits. molarity = 0 molality = 0

Answer 1

Solution:

resveratrol = C₁₄H₁₂O₃

The molar mass of resveratrol is 228.25 g/mol.

Thus: (18. g C₁₄H₁₂O₃ ) × (1 mol C₁₄H₁₂O₃ / 228.25 g C₁₄H₁₂O₃) = 0.07886 mol C₁₄H₁₂O₃

Density is the ratio of mass to volume.

Therefore,

Mass of 250 mL of solvent = (250 mL × 0.87 g/mL) = 217.5 g = 0.2175 kg

Molarity is defined as number of moles of solute dissolved in 1 L of solution.

Therefore,

Molarity = (0.07886 mol / 0.25 L) = 0.315 M = 0.32 M

Molarity = 0.32 M

Molality is defined as number of moles of solute dissolved in 1 kg of solvent.

Therefore,

Molality = (0.07886 mol / 0.2175 kg) = 0.3626 m = 0.36 m

Molality = 0.36 m

Answer:

Molarity = 0.32 M

Molality = 0.36 m