what is boiling point elevation and freezing point depression? does anyone know how to calculate these things and where to find them in the text? Its on chem ILT 3 although I have never heard of it b4...
Thanks,
So boiling point elevation is the phenomenon where the presence of solute particles in water increases the boiling point of solution. It also turns out that the presence of solute particles decreases the freezing point of the solution. These are colligative properties.
Turns out that both these properties are dependent on the total amount of solute present per amount of solvent (this is measured in molality - mol of solute/kg of solvent). So for instance, the presence of 1 mol of glucose in 1 kg of water will have the same effect as 0.5 mol of NaCl (which has 1 mol of solute particles as NaCl dissociates into Na+ and Cl-) on the boiling point elevation and freezing point depression.
Also turns out that the change in temperature is proportional to the amount of SOLUTE PARTICLES (mol) per mass of water (kg).
boiling point elevation:
temperature increase = molality (amount in moles of SOLUTE per kilogram of SOLVENT) x constant x van 't Hoff factor
= amount of solute particles per kilogram of solvent x constant
boiling point elevation:
temperature increase = molality (amount in moles of SOLUTE per kilogram of SOLVENT) x constant x van 't Hoff factor
= amount of solute particles per kilogram of solvent x constant
Van 't Hoff factor is simply to take into account that dissolving say 1 mol of NaCl in 1 kg of water produces a solution with 2 moles of solute particles per kg of water. The molality NaCl in solution is 1 mol/kg, but the amount of solute particles per kg of water is 2 mol/kg. The van 't Hoff factor in this case is 2. If you dissolve FeCl3 in solution the Van 't Hoff factor is 4. If MgCl2, Van 't Hoff factor = 3. And so on.
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