[Evaldas]

Exercise: What volume of 3 mol/l NaCl solution (density 1.12g/cm³) is needed to add to 200 g of water in order to get a 10% solution?

If I understand correctly
200+x - 100%
x - 10%
to 200g of water we would need to add x=22.22g of NaCl to get 10% solution, but in this case we need to use a 3mol/l solution so I'm confused, how to calculate this....

[Arkcon]

OK, can you use the definition of mol to convert mol/L into g per L?  Then you'll be able to calculate the volume needed.

[Evaldas]

Then 3 mol/l NaCl solution is 3x58.5g/1l=175,5g/l solution

[Evaldas]

I still don't understand?

[Arkcon]

So if there are 175,5g/l, what volume do you need to equal the grams you calculated before?

[Evaldas]

175.5 g - 1l
22.22 g - x l
x=22.22/175.5=0.126l?
But the thing is that now we have 200g of water plus 22.22g of NaCl and also y grams of water that is in the 0.126l 3 mol/l solution, so the solution is less than 20%. It would be 20% if we added 22.22g of pure NaCl to 200g of water.