Diluting of Solutions

Purpose: To be able to make solutions less concentrated from a more concentrated solution.

Equation

M1L1 = M2L2    , where M1 represents molarity and L1 represents volume before the solute is diluted into less concentrated. The moles of solute must be the same. Only the less concentrated solution contains more water.

Example:

Concentrated NaCl is 10.2 mole/L. How would you make up 300 mL of 0.620 mole/L HCL ?

We know that L2 = 300 mL    M1 = 10.2 mole/L   M2 = 0.620 mole/L
L1 is unknown. So we rearrange the equation above. You get:
L1 = M2 X L2 / M1  = 0.620 mole/L X 300 mL / 10.2 mole/L
                                 = 18.23529 L
* note the sig fig.
Answer = 20 L

Then, convert 300 mL into L, which is 0.300 L. To calculate how much water is added to the solute,
20 - 0.300 = 19.7 L

To get more practice, here is a worksheet with answers to the questions!
Hope this helps~!