posted by shanta .
calculate the value of water that is needed to dissolve 1.11 g of CaCl2 in order to prepare a 0.0250 M CaCl2 solution?
Remember the definitions.
Molarity = # mols/L.
and # mols = g/molar mass.
How many moles CaCl2 do you have in 11.1 g CaCl2. That will be 11.1 g CaCl2/molar mass CaCl2.
Then #mols = M x L.
You have M and you have mols, calculate L.
The procedure suggested by DrBob 222 will give the correct answer to the question. However, the wording of the question itself could be improved. It might be:
"Calculate the total volume of solution (water + CaCl2) when a 0.0250 M CaCl2 solution is prepared by dissolving 1.11 g of CaCl2 in a small volume of water and diluting to the calculated volume.".
The amount of water added cannot be calculated with complete precision since the volume of the solution includes both, water and calcium chloride.
GK is correct; the problem could have been worded more correctly. I assumed you were asking for the solution. Also, I note that I made an error in typing. It isn't 11.1 g CaCl2 but 1.11 g CaCl2.