Chemistry serial dilution

Question

When diluting your samples, you plan to have the following dilutions of blood to water: 1:10, 1:100, 1:1,000, 1:2,000, and 1:10,000. You need 100μL of each dilution. Provide the volume of blood and water for each of the dilutions you will have to prepare.

how would you use serial dilution to prepare the same dilutions described: 1:10, 1:100, 1:1,000, 1:2,000, and 1:10,000?

question with help needed in bold

Answer 1

Dilution factor = volume of solute / (volume solute + volume solvent)

So let's start with the 1:10 dilution. Let's take 1 ml of blood and combine it with 9 ml of water.

1 ml blood / (1 ml blood + 9 ml water) = 1:10 dilution factor

From this starting 1:10 solution, you can pipette out 100 μL to store for further use.

After that let's also pipette out 1 ml of this 1:10 solution and begin the serial dilution.

Total dilution factor for serial dilutions = previous dilution factor x next dilution factor

A 1:10 dilution factor x another 1:10 dilution factor gives us 1:100

another way of seeing this is 10^-1 x 10^-1 = 10^-2

So if we add this 1ml of the 1:10 solution to 9ml of water then we get a tube of 1:100 total dilution factor. We can pipette off 100 μL of this 1:100 solution for storage. We can then also pipette out 1 ml of the 1:100 solution to dilute again.

1:100 x 1:10 = 1:1,000

So add your 1 ml of 1:100 solution to 9 ml of water to get your 1:1,000 solution.

Store 100 μL. Pipette out 1 ml of 1:1,000 solution for further dilution.

1:1,000 x 1:10 = 1:10,000

Add 1 ml of 1:1,000 solution to 9 ml of water to make 1:10,000 solution.

Store 100 μL.

Almost done, we just need the 1:2,000 sample now. So go back to your tube of 1:1,000 solution and pipette out 1 ml.

1:1,000 x 1:2 = 1:2,000

So add this 1 ml of 1:1,000 solution to 1 ml of water to make the 1:2,000 solution.

Remember 1:2 dilution factor = 1 ml previous sample / (1 ml previous sample + 1 ml water)

Store 100 μL.

All done!

Alternatively you could make the 1:2,000 solution first, then further dilute this to get your 1:10,000 solution.

1:2,000 x 1:5 = 1:10,000

To make 1:5 solution need 1 ml previous sample / (1 ml previous sample + 4 ml water)