# Dilutions question

## Homework Statement

To what volume shuould you dilute 125 mL of an 8.00 mL CuCl2 solution so that 50.0 mL of the diluted solution contains 5.9 g CuCl2?

## Homework Equations

M= mol solute / vol solution (L)
m = mol solute / mass solvent (kg)
mole percent = mol solute / mol solute + solvent

## The Attempt at a Solution

8.00 M = mol CuCl2 / .125 L
1 mol CuCl2 x (65.55 + 2(35.45)g / 1 mol CuCl2 = 134.45 g CuCl2
5.9 g CuCl2 (final) x (1 mol CuCl2) / (65.55 +2(35.45)g = .4388 mol CuCl2
8.00 M = .44 mol CuCl2 --> .055 L solution???????????
I don't know how to use these formulas to find the diluted amount using the old amount? Do I subtract the grams CuCl2 to the new Molarity and find the tot vol? The answer is not the same as the back of the book.
THANKS SO MUCH!

Borek
Mentor
How many moles of CuCl2 do you have?

What molarity do you need?

C=n/V

Vapor Pressure Problem

An aq CaCl2 colution has a vapor pressure of 81.6 mmHg at 50 degrees C. The vapor pressure of pure water at this temperature is 92.6 mmHg. What is the concentration of CaCl2 in mass percent?

I don't even know where to start, if I can use Raoult's Law or not . . .

Borek
Mentor
You can. Just assume that whatever is dissolved has a vapor pressure of zero.

The question doesnt even make any sense.

you have 0.125dm3 of 8 molar CuCl2 and you want to turn it into 0.050dm3 of CuCl2?