Question

When a 1.06 g sample of Compound Q, a nonelectrolyte, is dissolved in 11.6 g of water, the boiling point of the resulting solution is 100.47 ˚C. The boiling point of pure water is 100.00 ˚C, and the Kb for water is 0.512 ˚C/m. Determine the molar mass of Compound Q.

Answer 1

Answer:

The molar mass of compound Q is 100 g/mol

Explanation:

Step 1: Data given

Mass of compound Q = 1.06 grams

Mass of water = 11.6 grams

Boiling point of the solution = 100.47 °C

Boiling point of water = 100.00 °C

Kb for water = 0.512 °C/m

Step 2: Calculate molality

ΔT = i*kb*m

⇒ with ΔT = the boiling point elevation = 0.47 °C

⇒ with i = the van't Hoff factor = 1

⇒ with kb = the boiling point elevation constant = 0.512 °C/m

⇒ with m = the molality = moles compound Q / mass water

m = ΔT / (i*Kb)

m = 0.47 / 0.512

m = 0.918 molal

Step 3: Calculate moles of Q

Molality = moles Q / mass H2O

moles Q = 0.918 molal * 0.0116 kg

moles Q = 0.0106 moles

Step 4: Calculate molar mass

Molar mass Q = mass Q / moles Q

Molar mass Q = 1.06 grams / 0.0106 moles

Molar mass Q = 100 g/mol

The molar mass of compound Q is 100 g/mol