the following questions are about colligative properties:
a)How much would the freezing point change in a 2.5 solution of phenol in benzene?
b)how much would the boiling point change in a 1.m solution of magnesium chloride in ethanol?
c)Does adding sugar to water raise or lower the vapor pressure of water? why?
a) delta T = Kf*m
b) delta T = *Kb*m
c) The vapor pressure is ALWAYS less (for ideal solution) when a non-volatile solute is added to a volatile solvent. Why? Think about the sugar molecules getting in the way of the water molecules and they (the water molecules) can't escape as easily.
To answer these questions about colligative properties, we need to know the respective formulas that relate these properties to the concentration of solute in the solvent.
a) The formula to calculate freezing point depression due to a nonvolatile solute is given by ΔTf = Kf·m, where ΔTf is the change in freezing point, Kf is the cryoscopic constant, and m is the molality (moles of solute per kilogram of solvent). We would need to know the value of the cryoscopic constant for benzene and the molality of the phenol solution to calculate the freezing point change.
b) The formula to calculate boiling point elevation due to a nonvolatile solute is given by ΔTb = Kb·m, where ΔTb is the change in boiling point, Kb is the ebullioscopic constant, and m is the molality. Similar to the previous question, we would need to know the value of the ebullioscopic constant for ethanol and the molality of the magnesium chloride solution to calculate the boiling point change.
c) Adding sugar to water lowers the vapor pressure of water. This phenomenon is explained by Raoult's law, which states that the vapor pressure of a solvent above a solution is directly proportional to the mole fraction of the solvent in the solution. When sugar is added to water, it creates an obstruction to the escape of water molecules into the gas phase, resulting in fewer water molecules being able to evaporate. Consequently, the vapor pressure of water is reduced.