How much water must be added to 1500 mL of a 6.0 mol/L #CaCl_2# solution to make the concentration of the resulting solution 2.0 mol/L?

1 Answer
Jan 26, 2017

Answer:

You need to add another #"3 litres"# of water........

Explanation:

The defining relationship for #"concentration"# is,

#"Concentration"# #=# #"Moles of stuff"/"Volume of solution"#, now typically the solvent is water, but it could be other materials, even a gas.

Here we have a molar quantity of #6.0*mol*L^-1#, and a #1500*mL# volume. We wish to dilute this concentration by a THIRD to #2.0*mol*L^-1#.

Now clearly, we cannot get the calcium salt out of solution, but we can add more solvent, more water to dilute it.

And here we can use the old relationship,

#C_1V_1=C_2V_2# where #C="concentration"#, and #V="volume"#.

So we solve for #V_2=(C_1V_1)/C_2=(1500*mLxx6.0*mol*L^-1)/(2.0*mol*L^-1)=4500*mL#.

And since we began with #1500*mL#, another #3000*mL# are required.