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.
The answer:
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:
Where: |
||
M_{1} | = | Concentration 1 |
V_{1} | = | Volume 1 |
M_{2} | = | Concentration 2 |
V_{2} | = | Volume 2 |
M_{1} | = | Concentration 1 | = | 10 mg/ml |
V_{1} | = | Volume 1 | = | Unknown X |
M_{2} | = | Concentration 2 | = | 1.5 mg/ml |
V_{2} | = | Volume 2 | = | 5 ml |
or:
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....
If you struggle with 'Science Maths' then you may like to look at Maths4Biosciences.
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