Stupid molality question

[spyderracing32]

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Ok so when calculating molality I am confused about electrolyte solute species. Say I have 1mol of NaI in 1kg Water. Is this going to be 1m or 2m because the NaI solvates into the two ions? And for whatever choice you give, is this always the case?

 

[rocuronium]

Molality is defined as the number of moles of solute per kilogram of solvent.

In your example, since you are using one mol of solvent in one kilogram of solvent, the solution would be 1.0 molal.

Even when the solute is solvated, the solution is still one molal with respect to each ion.

 

[riceman04]

I think what may be confusing is that in some instances you do have to consider the formula i times m (or M) in certain instances

 

[rocuronium]

I think what may be confusing is that in some instances you do have to consider the formula i times m (or M) in certain instances

That comes into account when you are dealing with colligative properties such as freezing point depression.

 

[spyderracing32]

I think what may be confusing is that in some instances you do have to consider the formula i times m (or M) in certain instances

Yea that's what was getting me, thanks for the responses guys. TPR does not do a good job about elucidating that distinction (Van 't Hoff factor).

 

[Vihsadas]

I think what may be confusing is that in some instances you do have to consider the formula i times m (or M) in certain instances

yeah, if they say 'molarity/molality of ions', rather than 'solute'. semantics really...