c1v1=c2v2 demo

Worried about how to calculate concentrations or volumes when you do dilutions? You might appreciate a little demo of C1V1 = C2V2 in action....

First some definitions:

C1 = The concentration of your stock solution

C2 = The final concentration after performing the dilution

V1 = The volume of your stock solution your need to take

V2 = The final volume your diluted sample will have

Ok, so lets say we have a stock solution of 1M of NaCl.

We want to have 500mM NaCl AND we want our diluted sample to be 2mls total volume.

How much of our stock solution will we need?

Lets look at this again, but this time I have written in where the C1 V1 C2 and V2 are:

We have a stock solution of 1M of NaCl (C1) .

We want to have 500mM NaCl (C2) AND we want our diluted sample to be 2mls total volume (V2).

How much of our stock solution will we need (V1)?

So, now you just need to slot all this in to the wonderful C1V1 = C2V2:

C1 x V1 = C2 x V2 

1M x V1 = 500mM x 2mls  

--> Be careful, the concentrations are in two different units - they need to be the same for this to work...

1000mM x V1 = 500mM x 2mls  or   1M x V1 = 0.5M x 2mls  would both be fine

then rearrange and solve for V1:

V1 = 500 x 2 / 1000           or      V1 = 0.5 x 2 / 1

Both will give you V1 = 1ml

This means that you will have to take 1ml of the 1M NaCl stock solution and add it to 1ml of water (so that your final volume is 2mls) to make the diluted sample of 500mM NaCl.

So long as you know three things from the C1V1 = C2V2 equation, you can rearrange it to find the fourth.

This was an easy example that you might have been able to see the answer to without doing the calculation, but things won't always be this simple!

Does that make sense to you all?