Menthol is a crystalline substance with a peppermint taste and odor. when 1.48 g of menthol is dissolved in 25.0 g of cyclohexane, the freezing point of the solution is lowered by 7.90 °c. the freezing point and kf constant for cyclohexane can be found here. calculate the molar mass of menthol.

Molar mass of menthol is 155.86 g/mol

Explanation:

Let's apply the colligative property of freezing point depression:

ΔT = Kf . m . i

As menthol is an organic compound we assume the i (Van't Hoff factor as non electrolytic, so i = 1)

m = mol /kg (molality)

Kf = Cryoscopic constant, in this case, for cyclohexane

ΔT = T° freezing of pure solvent - T° freezing solution

7.90°C = 20.8°C / m . m . 1

7.90°C / 20.8 m/°C = m

0.380 m = molality

0.380 moles are the moles of solute (menthol) dissolved in 1kg of solvent, but our mass of solvent is 25 g.

Let's convert the g of solvent to kg to work with molality

25 g = 0.025 kg

molal . solvent mass = moles of solute

0.380 mol /kg . 0.025kg = 9.49×10⁻³ moles

Now, we have the moles and the mass of solute. Let's determine the molar mass of menthol (grams / moles)

1.48 g / 9.49×10⁻³ m = 155.86 g/m

the density(ratio between mass and volume as m/v) decreases from top to bottom in periodic table group as the size increases and nuclear charge decreases. but in periods density increases from left to right as atom size decreases and nuclear charge increases.

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