Colligative Properties

[aclementine]

Which of the following is NOT a colligative property?
a) freezing point depression
b) osmotic pressure
c) melting point depression
d) boiling point elevation
e) vapor pressure lowering

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[ZzZzSleepyhead]

Which of the following is NOT a colligative property?
a) freezing point depression
b) osmotic pressure
c) melting point depression
d) boiling point elevation
e) vapor pressure lowering

Melting point depression.

 

[aclementine]

the right answer is "c) melting point depression"... but how come? I have always thought that freezing point depression was the same as melting point depression, right?

 

[Blarelli]

Melting point depression has to do with size of the particles being melted, while colligative properties have to do with amount of solute in a solution.

 

[aclementine]

but isn't melting point by definition the same as freezing point?

therefore, freezing point depression (due to addition of solute) should be the same as melting point depression, right? Both decreases are related to the amount of solute added, and nothing to do with the size of particles, right?

 

[Blarelli]

but isn't melting point by definition the same as freezing point?

therefore, freezing point depression (due to addition of solute) should be the same as melting point depression, right? Both decreases are related to the amount of solute added, and nothing to do with the size of particles, right?

You're missing the point. Melting point depression is its own idea. Yes, melting point and freezing point can be looked at as the same, but melting point depression refers to a depression in melting point as the material comes in smaller quantities.

 

[wantVCUdental]

You're missing the point. Melting point depression is its own idea. Yes, melting point and freezing point can be looked at as the same, but melting point depression refers to a depression in melting point as the material comes in smaller quantities.

I don't know the answer, but whenever i see quantity i relate it to colligative property, so i too don't understand this...

 

[Blarelli]

I don't know the answer, but whenever i see quantity i relate it to colligative property, so i too don't understand this...

In this case, all I can think to tell you is this is one of those principles that you have to memorize the definition to know it doesn't belong with the colligative properties.
A simple example of melting point depression is that a nano-gram of a certain crystal will melt at a lower temperature than a gram sized crystal.

 

[minotaur9]

good question...I'm still confused too, guess we'll just have to memorize it