[Mani]

Hi,
There is a solution of calcium chloride (CaCl2) in water that I need to know its percent composition.
These are the information on the label of this vial:

20mL
25mmol
CaCl2

I wonder if by these information one can calculate its percent composition.

Thanks,
Mani

[Borek]

Yes, it is possible, but you need to explain more precisely what you are looking for. Mass percentage of elements, or will it be enough to find the mass percentage of CaCl₂ and water?

In both cases you have to start with the definition of mass percentage (I am assuming you want it to be mass percentage - am I correct?). Calculate amount of the element (or compound), calculate its mass, use mass percentage definition. You will need solution mass - and you can calculate it assuming its density is that of pure water, 1.00 g/mL (for 25 mM CaCl₂ solution exact density is 1.0006 g/mL, so this assumption is quite good).

[Mani]

Yes, it is possible, but you need to explain more precisely what you are looking for. Mass percentage of elements, or will it be enough to find the mass percentage of CaCl₂ and water?

In both cases you have to start with the definition of mass percentage (I am assuming you want it to be mass percentage - am I correct?). Calculate amount of the element (or compound), calculate its mass, use mass percentage definition. You will need solution mass - and you can calculate it assuming its density is that of pure water, 1.00 g/mL (for 25 mM CaCl₂ solution exact density is 1.0006 g/mL, so this assumption is quite good).

Hi,
Thanks for your reply. Basically I'm asked to make a %10 solution of CaCl2 out of mentioned solution. So I think I just need to know mass percentage of CaCl2 of this solution.
As I'm not a chemistry geek, I would need more explanation as to how should I calculate it.

Thanks again,
Mani

[Borek]

Basically I'm asked to make a %10 solution of CaCl2 out of mentioned solution. So I think I just need to know mass percentage of CaCl2 of this solution.

Strange. If it is 25 mM you have to get rid of most of the water to concentrate the solution - that means evaporating almost everything. Are you sure you are not missing something?

Finding mass percentage in this case doesn't make much sense. Find mass of the dissolved CaCl₂, then find mass of the 10%w/w solution that will contain this amount of calcium chloride. Dry the solution you have to obtain the solid. Knowing mass of CaCl₂ and final mass of the solution you can easily calculate how much water you have to add. You will need a tiny pipette for that.

[Mani]

Basically I'm asked to make a %10 solution of CaCl2 out of mentioned solution. So I think I just need to know mass percentage of CaCl2 of this solution.

Strange. If it is 25 mM you have to get rid of most of the water to concentrate the solution - that means evaporating almost everything. Are you sure you are not missing something?

Finding mass percentage in this case doesn't make much sense. Find mass of the dissolved CaCl₂, then find mass of the 10%w/w solution that will contain this amount of calcium chloride. Dry the solution you have to obtain the solid. Knowing mass of CaCl₂ and final mass of the solution you can easily calculate how much water you have to add. You will need a tiny pipette for that.

It seems much more complicated than what I thought before!:(
Thanks a lot,
M.