# How do you calculate serial dilutions?

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Hint: As we know that serial dilution is basically a series of dilutions done sequentially. These are performed to convert a dense solution into a more usable concentration.

- It is found that dilution method is used to estimate the concentration of an unknown sample.
- Basically serial dilution involves the process of taking a sample diluting it by a series of volumes (standard) of sterile diluent, that can be 0.9% saline or can be distilled water.
- Further, a series of spread plates is made by a small measured volume of each dilution. It is found that serial ten-fold or serial ten-fold dilutions are commonly used to prepare the diluted analytes in laboratory.
- We can calculate the dilution factor in a serial dilution. The dilution factor of each tube in a set can be calculated by using the formula:
$\dfrac{volume\text{ }of\text{ }sample}{volume\text{ }of\text{ }sample+volume\text{ }of\text{ }diluent}$
- It is found that for a ten-fold dilution, generally one ml of sample is added to nine ml of the diluent. Then, in this case dilution factor of that test tube can be calculated by using the formula:
$dilution\text{ }factor=\dfrac{1ml}{1ml+9ml}=\dfrac{1}{10}={{10}^{-1}}$
- Now, for the total dilution factor, the total dilution factor for the second tube is equal to the dilution of the first tube multiplied by the dilution of the second tube.
- Hence, in this way we can calculate the serial dilutions.

Note:
- It is found that serial dilution method is mainly performed to avoid having to pipette very small volumes to make dilution of a solution.
- Let’s see an example to calculate the dilute factor:
If for the first tube the dilution factor is =${{10}^{-1}}$and for the second tube the dilution factor is =${{10}^{-1}}$. Then, the total dilution factor will be= ${{10}^{-1}}\times {{10}^{-1}}={{10}^{-2}}$