Yes, molality does affect vapor pressure. The vapor pressure of a solvent is lowered when a solute is dissolved in it, and the extent of this lowering is influenced by the molality (moles of solute per kilogram of solvent).
According to Raoult's law, which applies to ideal solutions, the vapor pressure of a solvent above a solution is directly proportional to the mole fraction of the solvent present. The mole fraction of the solvent is determined by the molality of the solution. Therefore, as the molality of the solute increases, the mole fraction of the solvent decreases, resulting in a lower vapor pressure.
This phenomenon can be explained by the fact that the solute particles occupy space on the surface of the solvent, making it more difficult for the solvent molecules to escape and enter the vapor phase. As a result, the vapor pressure of the solution decreases compared to the pure solvent.
It's important to note that Raoult's law assumes ideal behavior of both the solvent and solute, and it is most accurate for dilute solutions. In reality, deviations from Raoult's law can occur, particularly for concentrated or non-ideal solutions, where interactions between solute and solvent particles become significant. In such cases, other factors such as solute-solvent interactions, association or dissociation of solute species, and non-ideal behavior of components may affect the vapor pressure.