Barbiturates are synthetic drugs used as sedatives and hypnotics. Barbital (184.2 g/mol) is one of the simplest of these drugs. What is the boiling point of a solution prepared by dissolving 42.5 g of barbital in 825 g of acetic acid? (For pure acetic acid, K_b = 3.07°C/m; boiling point of pure acetic acid = 117.9°C) A) 117.0°C B) 117.7°C C) 118.1°C D) 118.8°C E) 120.4°C

Question

Quizplus · Accepted Answer

First, we need to calculate how many moles of barbital are in the solution:
n(barbital) = mass/molar mass = 42.5 g / 184.2 g/mol = 0.2307 mol
Next, we need to calculate the molality of the solution:
molality = moles of solute / mass of solvent in kg
mass of solvent = 825 g = 0.825 kg
molality = 0.2307 mol / 0.825 kg = 0.280 mol/kg
Now we can use the boiling point elevation equation:
ΔTb = Kb * molality
Kb for acetic acid = 3.07°C/m
ΔTb = 3.07°C/m * 0.280 mol/kg = 0.8616°C
The boiling point of the solution is:
boiling point = boiling point of pure solvent + ΔTb
boiling point = 117.9°C + 0.8616°C = 118.8°C
Therefore, the best choice is D, with the correct boiling point of the solution.

Barbiturates Are Synthetic Drugs Used as Sedatives and Hypnotics