Question

A solution is made by dissolving 58.125 g of sample of an unknown, nonelectrolyte compound in water. The mass of the solution is exactly 750.0 g. The boiling point of this solution is 100.220 ∘ C . What is the molecular weight of the unknown compound?

Answer 1

To determine the molecular weight of the unknown compound, one would need to calculate the boiling point elevation, then the molality of the solution, and finally rearrange the formula to solve for the molar mass based on the given masses of solute and solvent.

Step-by-step explanation:

The student's question pertains to the calculation of the molecular weight of an unknown compound using the boiling point elevation method in Chemistry. To find the molecular weight of the unknown compound, the boiling point elevation (ΔTb) first needs to be determined, using the observed boiling point and the normal boiling point of water (100°C). Then, using the boiling point elevation constant (Kb for water), and the mass of the solute and solvent, the molality (m) of the solution can be calculated. The molar mass (M) of the unknown compound is then found by rearranging the formula ΔTb = i ⋅ Kb ⋅ m, where i is the van't Hoff factor (which is 1 for a nonelectrolyte compound) and solving for M.

Since we know the mass of the solute and solvent and the boiling point elevation, the molality can be calculated with m = (moles of solute) / (kilograms of solvent). The moles of solute is molar mass dependent, so when we rearrange to solve for molar mass, we get M = (mass of solute in grams) / (molality ⋅ kg of solvent).

To solve the problem, the steps are as follows:

• Determine the boiling point elevation (ΔTb) by subtracting the normal boiling point of water from the given boiling point of the solution.
• Calculate molality (m) using the boiling point elevation constant for water (Kb) and the determined ΔTb.
• Find the molar mass (M) by rearranging the formula to solve for M based on the mass of solute and the calculated molality.

Answer 2

195.52 g/mol

Step-by-step explanation:

Answer:

195.52 g/mol

Step-by-step explanation:

1.) ΔT = Kb * molality

2.) (100.22-100) = 0.512 * molality

3.) 0.22 = 0.512 * molality

4.) 0.22/0.512 =( 0.512 * molality)/ 0.512

5.) 0.4297 = molality

6.) molality = mol of solute/ kg of solvent

7.) 0.4297 = mol of solute / (0.750- 0.058125)

8.) 0.4297 = mol of solute / 0.69175

9.) (0.4297 = mol of solute / 0.69175) * 0.69175

10.) mol of solute = 0.29729

11.) mol = mass / mw therefore mw = mass/ mol

12.) mw = 58.125g / 0.29729mol

13.) mw = 195.125 g/mol

Please be mindful I did not consistently write conversions or write out units to show cancellations.