When you're thinking about dilution, it helps to simplify your actions into dilution factors. When we said the diluted coffee was
'1/10th as strong as the original'
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that was a dilution factor. We could also have said
'the dilution factor was 1/10', or
'the dilution factor was 0.1'.
Here are a few more for you to try:
- 1 mL coffee + 4 mL water =
- 1 mL coffee + 9mL water =
- 1 mL + 99mL water =
As you've probably guessed, this works exactly the same whether you're talking about caffeine or meningicocci. Here's what a dilution factor of 0.01 looks like on the lab bench:
Notice that it really doesn't matter how much of the original stock you started with, as long as you had enough to put 1 mL into the new container. What matters is how much you transfer and how much water you add.
Serial Dilution Experiment
It's possible to write an algebraic expression for the dilution factor, but it's almost more trouble than it's worth, because it sounds so complex. But for what it's worth, the dilution factor for 1 mL stock + 99 mL water is:
amount transferred / total amount =
amount transferred / (amount transferred + amount water added) =
1 / (1+99) = 1/100 = 0.01.
Below is an applet to practice finding dilution factors, and also to determine how much water to add to achieve a given dilution. You should practice this until it is second nature!!
1 mL stock + mL water
Can you do it in your sleep? OK, then go on to the next page...
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Copyright University of Maryland, 2007
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Serial Dilution Practice Problems
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How To Serial Dilution
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