(NR) DILUTIONS - March 3rd, 2011

Diluting solutions

- When two solutions are mixed the concentration changes.

-  Dilution is the process of decreasing the concentration by adding a solvent (usually water)

- the amount of solute doesn’t change.  n1 = n2

- because concentration is mol/L 

   We can write…

                  

        C=n/V          AND          n= CV          AND          V=n/C

So… 

C1V1 = C2V2

(initial) = (final)

EXAMPLES

A 12.0 mL of 38 M of hydrochloric acid is diluted to a final volume of 380 mL. What is the concentration of the new solution?

*REMEMBER TO CONVERT mL to L!

C1V1   =   C2V2

(38M)(0.012L)   =   C2(0.380L)

0.456mol   =   C2(0.380L)

1.2M   =   C2

Therefore new solution has a concentration of 1.2M

Mr. Doktor the ALMIGHTY chemist is given a solution of 3.8M NaOH. After diluting the solution to a final volume of 0.12L the concentration is 0.83M. What volume of NaOH was Mr. Doktor the ALMIGHTY chemist initially given?

C1V1   =   C2V2

(3.8M)V1   =   (0.83M)(0.12L)

(3.8M)V1   =   0.0996mol

V1   =   0.026L