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

Answer:

molecular weight (Mb) = 0.42 g/mol

Explanation:

mass sample (solute) (wb) = 58.125 g

mass sln = 750.0 g = mass solute + mass solvent

∴ solute (b) unknown nonelectrolyte compound

∴ solvent (a): water

⇒ mb = mol solute/Kg solvent (nb/wa)

boiling point:

• ΔT = K*mb = 100.220°C ≅ 373.22 K

∴ K water = 1.86 K.Kg/mol

⇒ Mb = ? (molecular weight) (wb/nb)

⇒ mb = ΔT / K

⇒ mb = (373.22 K) / (1.86 K.Kg/mol)

⇒ mb = 200.656 mol/Kg

∴ mass solvent = 750.0 g - 58.125 g = 691.875 g = 0.692 Kg

moles solute:

⇒ nb = (200.656 mol/Kg)*(0.692 Kg) = 138.83 mol solute

molecular weight:

⇒ Mb = (58.125 g)/(138.83 mol) = 0.42 g/mol

Answer 2

Answer:

195.52 g/mol

Explanation:

Answer:

195.52 g/mol

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.