If you're working in a chemistry lab, it's essential to know how to calculate a dilution.
- Dilutions: Explanations and Examples of Common Methods. There are many ways of expressing concentrations and dilution. The following is a brief explanation of some ways of calculating dilutions that are common in biological science and often used at Quansys Biosciences.
- WORKING DILUTION PROBLEMS It is a common practice to determine microbial counts for both liquid and solid specimens-suspensions of E. Coli in nutrient broth all the way to soil samples and hamburger meat.
Review of Dilution, Concentration, and Stock Solutions
Serial dilution examples Serial dilutions are a common practice in the natural sciences. Due to the period decrease in concentration, this method is very useful when performing many types of experiments, from chemistry to biology to medicine. To calculate CFU from bacterial dilution, you need to know the size of your sample and the size of dilution. Count only individual colonies (which look like distinct, separate dots) and aim for more than 30 colonies but less than 300 colonies. Jun 17, 2014 In serial dilutions, you multiply the dilution factors for each step. The dilution factor or the dilution is the initial volume divided by the final volume. For example, if you add a 1 mL sample to 9 mL of diluent to get 10 mL of solution, #DF = Vi/Vf# = #(1'mL')/(10'mL') = 1/10#.
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A dilution is a solution made by adding more solvent to a more concentrated solution (stock solution), which reduces the concentration of the solute. An example of a dilute solution is tap water, which is mostly water (solvent), with a small amount of dissolved minerals and gasses (solutes).
An example of a concentrated solution is 98 percent sulfuric acid (~18 M). The primary reason you start with a concentrated solution and then dilute it to make a dilution is that it's very difficult—and sometimes impossible—to accurately measure solute to prepare a dilute solution, so there would be a large degree of error in the concentration value.
Use the law of conservation of mass to perform the calculation for the dilution:
MdilutionVdilution = MstockVstock
Dilution Example
As an example, say you need to prepare 50 milliliters of a 1.0 M solution from a 2.0 M stock solution. Your first step is to calculate the volume of stock solution that is required.
MdilutionVdilution = MstockVstock
(1.0 M)(50 ml) = (2.0 M)(x ml)
x = [(1.0 M)(50 ml)]/2.0 M
x = 25 ml of stock solution
To make your solution, pour 25 ml of stock solution into a 50 ml volumetric flask. Dilute it with solvent to the 50 ml line.
Avoid This Common Dilution Mistake
![Serial Dilution Calculation Examples Serial Dilution Calculation Examples](https://bio.libretexts.org/@api/deki/files/4778/dilution4.png?size=bestfit&width=562&height=386&revision=1)
Microbiology Serial Dilution Examples
It's a common mistake to add too much solvent when making the dilution. Make sure you pour the concentrated solution into the flask and then dilute it to the volume mark. Do not, for example, mix 250 ml of concentrated solution with 1 liter of solvent to make a 1-liter solution.