Serial dilution problem

[bio_chem]

I'm a little stuck on a problem that requires me to explain how I would use the process of serial dilution to create solutions of 0.05mM, 0.10mM, 0.25mM, 0.5mM, and 1.5mM from a stock solution of 10mM. Normally, I see problems where the ratio between the solutions is equal, so you would basically take, for ex. 1mL from the stock, and mix it with 9mL of water, and repeat this process for the following dilutions. In this case, however, the ratios between the solutions are not equal (0.10mM is twice that of 0.05mM, while 0.25mM is 2.5 that of 0.10mM). If the ratios aren't equal between the solutions to prepare, then how should one go about using serial dilution?

 

Any help would be much appreciated!

[ewmon]

the ratios between the solutions are not equal ... how should one go about using serial dilution?

The word "serial" in "serial dilutions" only means that the next dilution is made from the previous dilution, and not that the dilution factors are the same. However, it is true that many or most serial dilutions that you will be asked to perform will have the same dilution factor (at least that's been my experience). So, line up the dilutions in decreasing order of concentration, and perform the-next-from-the-previous dilutions individually.

 

10mM →1.5mM → 0.5mM → 0.25mM → 0.10mM → 0.05mM

 

Alternately, in the situation you describe, a non-serial method could be where you make all the dilutions straight from the stock solution, but they would not be serial dilutions.

 

10mM →1.5mM

10mM → 0.5mM

10mM → 0.25mM

10mM → 0.10mM

10mM → 0.05mM