The type of question is:
You have been asked to dilute a 10 mg/ml solution to give 5 ml of a 1.5 mg/ml solution.
How many ml of water would you use?
How many ml of the stock protein solution would you use?
The way I would work this out is by saying that 5 ml of 1.5 mg/ml contains 5 x 1.5 mg = 7.5 mg.
If the stock is 10 mg/ml then I need to take a volume that would give 7.5 mg. So, the number of ml of the stock I need is 7.5 / 10 = 0.75 ml (that is, 0.75 ml of a 10 mg/ml solution contains 7.5 mg).
Therefore, I have 0.75 ml of the stock, and the final volume is 5 ml, so we need to add 5 - 0.75 = 4.25 ml of water.
How many ml of water would you use? 4.25 ml
How many ml of the stock protein solution would you use? 0.75 ml
Although I prefer to work it out as above you can use a formula:
|M1||=||Concentration 1||=||10 mg/ml|
|V1||=||Volume 1||=||Unknown X|
|M2||=||Concentration 2||=||1.5 mg/ml|
|V2||=||Volume 2||=||5 ml|
Rearranging to solve for Unknown X:
Using the formula is the same as the first solution, but in the first solution I don't have to remember the formula....
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