digdig

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If you make a .5L solution containing .5 mol of KCL, what is the molarity of the solution?

A. 0.1 M
B. 0.2 M
C. 1 M
D. 2 M
E. 10M

Answer is 1 M. but i picked 2 M because of the dissociation of KCL. Can anyone tell me when we consider this. I know we take into account in boiling point and freezing point depression. but i thought it should apply here also. 0.5 mol of KCL would mean .5 mole K and .5 mole Cl. so total of 1 mole. so 1mole/.5L = 2M !!!!
this is frustrating. any help would be greatly appreciated.
 

KTDMD

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digdig said:
If you make a .5L solution containing .5 mol of KCL, what is the molarity of the solution?

A. 0.1 M
B. 0.2 M
C. 1 M
D. 2 M
E. 10M

Answer is 1 M. but i picked 2 M because of the dissociation of KCL. Can anyone tell me when we consider this. I know we take into account in boiling point and freezing point depression. but i thought it should apply here also. 0.5 mol of KCL would mean .5 mole K and .5 mole Cl. so total of 1 mole. so 1mole/.5L = 2M !!!!
this is frustrating. any help would be greatly appreciated.
I guess you're confused here with molarity vs molality. Try revert to your basic understanding on these two and you should find out the answer for yourself easily.
 

bluesdeluxe

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Here is how I thought of it initially and got it right

Molarity is defined as moles of solute over 1 L solution. Since you have .5 L or solution you simply multiply .5/.5 by 2 and get 1/1 = 1 M. Can't ask for an easier question on the dat
 
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digdig

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so we do not consider dissociation of KCl to give a total of 1 mol of solutes??
 

KTDMD

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digdig said:
so we do not consider dissociation of KCl to give a total of 1 mol of solutes??
Definitely not. This belongs to colligative properties of molality, where as the question here deals with concentration (molarity). They are practically two different chemistry terms/concepts.