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The concept of dilutions, including how to calculate dilution factors and undiluted concentrations from diluted concentrations. It also covers the process of performing multiple dilutions and using different solvents for dilution.
Typology: Lecture notes
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Let’s say we had a test tube with a sample (Green) that was at a 3.0 M concentration. And we had a test tube with some water.
Sample Water
If we took 1 mL of Sample and place it in a new tube, and then added 4 mL of water. Then Mix.
1 mL or 1 volume
4 mL or 4 volumes mix->
We have just made a dilution. The total volume is 5 mL ( or 5 total volumes). To calculate the dilution factor (df) we divide the total volumes by the volumes of sample.
Now you may hear different terms to express this dilution, like:
“The dilution factor is 5" “It was a 5 fold dilution” “It was diluted 1/5"
These all mean the same thing, that there is 1 volume part of sample and 4 volume parts of whatever liquid is being used to dilute the sample for a total of 5 volume parts.
To calculate the concentration of our diluted sample we multiply by the inverse of our dilution factor.
Often we wish to work backwards. Let’s say we had a sample that had been diluted 1/5 that has a concentration 0f 0.60 M. What was its undiluted concentration?
Therefore we take our concentration and multiply by our dilution factor.
In other words by doing two 1/5 dilutions. Our final dilution ends up being a 1/25 dilution. In other words our sample has been diluted 25 fold. (d.f. = 25)
This means that in this, there is 1 volume part sample to 24 volume parts of water for a total of 25 parts.
If we wanted to work backwards. If our diluted sample was 0.12 M and it had been diluted 25 fold - what was its undiluted concentration?
Remember: We don’t always dilute samples with water ... we may instead use a buffer solution to dilute or perhaps some other solvent.
Though the terms used are different, ... this concept isn’t new. Remember C V =C V? 1 1 2 2
