When 177. g of alanine (C3H7NO2) are dissolved in 800.0 g of a certain mystery liquid X, the freezing point of the solution is 5.9 °C lower than the freezing point of pure X. On the other hand, when 177.0 g of potassium bromide are dissolved in the same mass of X, the freezing point of the solution is 7.2 °C lower than the freezing point of pure X. Calculate the van't Hoff factor for potassium bromide in X. Be sure your answer has a unit symbol, if necessary, and is rounded to the correct number of significant digits.

Van't Hoff factor of KBr is 1.63

Explanation:

Freezing point depression due the addition of a solute follows the formula:

ΔT = Kf×m×i

Where ΔT is change in freezing point, Kf is freezing point depression constant of the solvent X, m is molality of the solution (mol / kg) and i is Van't Hoff factor.

Moles of 177g of alanine (Molar mass: 89.09g/mol) are:

177g × (1mol / 89.09g) = 1.99 moles. In 0.800kg:

1.99mol / 0.800kg = 2.49m

Replacing in freezing point depression formula:

5.9°C = Kf×2.49m×1

Alinine has a Van't Hoff factor of 1

The Kf of the solvent is:

2.37 °C/m

Molality of the 177.0g of KBr solution (Molar mass: 119g/mol) is:

177.0g × (1mol / 119g) = 1.487 moles / 0.800kg = 1.859m

And the freezing point depression formula is:

7.2°C = 2.37°C/m×1.859m×i

1.63 = i

Van't Hoff factor of KBr is 1.63

vanderwaal's forces of attraction are the electrostatic intermolecular forces that exist in a molecule due to the temporary or permanent dipoles that are developed in a molecule. in , the major intermolecular forces are dipole-dipole interactions as the molecule is polar (bent structure). so the vanderwaal's forces of interaction in between molecules are the permanent dipole-dipole interactions that develop due to the dipole that exists in between the polar h - s bond. the positively charged hydrogen atom is attracted towards the negative end of the dipole that is sulfur of the adjacent molecule. therefore, these forces of attraction are relatively stronger than that of london dispersion forces that exist in non polar molecules.