Pure Cyclohexane, C₆H₁₂, Has a Molar Mass of 84

Short Answer

Pure cyclohexane, C₆H₁₂, has a molar mass of 84.161 g mol⁻¹, a density of 0.7785 g mL⁻¹, a freezing point of 6.53°C, and a boiling point of 80.72°C. Its freezing point depression and boiling point elevation constants are: K_f = 20.0 °C m⁻¹; K_b = 2.69 °C m⁻¹. A solution was made by taking 9.50 g of an unknown nonelectrolyte and dissolving it in 125.0 g of cyclohexane. The measured freezing point of the solution was -0.78^°C. Calculate the molar mass of the unknown substance.Hint: Find molality, then moles, then molar mass, being sure to keep track of units.