Sunday 11 March 2012

Dilutions

Dilutions - when 2 solutions are mixed the concentration changes
                - the process of decreasing the concentration by adding a solvent(usually water)
                - the amount of solute does not change, only the volume
                - because concentration is mol/L we use the following equations: 
                                       C=n/v and n=Cv  so that    C1V1=C2V2
*always remember to convert mL into L

EX.
How much water must be added to 10.0mL of 10.0M Na2SO4 to give a solution with a concentration of 0.50M?

V1=100mL-->.10L               C1V1=C2V2
C1=0.10M                            
C2=400mL                           C1V1 = V2    ---->  (10.0)(10) = 200mL         changeV=200-10=190mL
                                               C2                             (0.50)

EX.
If a 75.0mL sample of 0.500M KCl is added to 100mL of 0.250M KCl what will the resulting solutions concentrations be?

0.075L x 0.500M = 0. 0375mol               
                   L

0.100L x 0.250M = 0.025mol
                   L
Then add both mols together,
0.0375+0.025= 0.0625mol

After divide the mols by adding both amounts of litres together,
0.0625M = 0.357M
0.175L


Janine R


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