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Colligative Properties - Concept

Teacher/Instructor Kendal Orenstein
Kendal Orenstein

Rutger's University
M.Ed., Columbia Teachers College

Kendal founded an academic coaching company in Washington D.C. and teaches in local area schools. In her spare time she loves to explore new places.

Colligative properties are the properties of a solution as a whole and depend on the concentration. The colligative properties include freezing point depression, boiling point elevation, vapor pressure lowering and osmotic pressure.

Alright. Let's talk about colligative properties solutions and colligative properties are a collection of physical properties of the solution that are affected by the number of solute particles. So properties of solutions are going to be different from the properties of the actual solvent by itself. And the things that, there are four things that are going to be affected by this. One's going to be vapor pressure, and actual vapor pressure of the solution versus its solvent will lower, the other one, another one is boiling point and the boiling point of the solution will be higher than the boiling point of the solvent alone. The freezing point of the solution will be lower than the actual solvent by itself and the osmotic pressure is going to increase, compared to a solvent by itself. And this will depend on the molality, molality not molarity, molality of the solution. And molality is moles of solute over kilograms of solvent, and don't forget the density of water is one gram per millilitre. So we can just change number of litres to kilograms, they'll be the sa-, it should be the same conversion because the density of water is one. And don't forget that the unit for that the symbol for molality is a small m.

So thi- this will depend, this molality is what's going to show how much all these guys are affected. So let's talk about different types of things that should be in a solution. So you have electrolytes and as you should remember electrolytes are things that conduct electricity in solution or ionic compounds and ionic compounds as you know will break up in solutions. So for example we have sodium chloride. When you put sodium chloride in water, it will actually break up into sodium ion and a chloride ion. So if you put one molal of sodium chloride in solution, you'll actually get two molals of product, of particle in your so- in your solution. So it will actually break up and you know that your solute is going to be an electrolyte.

Also if it's an electolyte that has like calcium chloride that has more than you know just two particles those will break up and actually three particles of every one. So if it's one molal of calcium chloride you actually need three molals of particles which will affect this more than sodium chloride will affect it even if they were the same amount. Also, non-electrolytes, non-electrolytes do not break up in solutions so however amount you put in solution is the amount that you actually, the amount of particles will actually be in the solution.

So, for example here is table sugar which we know is a molecular compound. If we put one molal of a non-electrolyte, it will just be the same. These are not going to break up into its atoms. So it will stick together. It will break up from each other but it'll stick together in terms of the compound. So given one molal of a non-electrolyte, you are going to end up with one molal of particles of non of the non-electrolyte. So this is actually going to play a big part in dealing with the co- colligative properties, the solutions, boiling point, freezing point and vapor pressure and osmotic pressure. And we'll talk about others in each separate video.