Calculation help - (May/05/2018 )

Hi,

I have to make a solution and add it to the complete growth media (CGM) at 10 µM concentration.

The manufacturer says, to make the solution at 50 mg/ml working concentration. How can I calculate to get a concentration of 10 µM?

The final volume of the CGM with 10 µM concentration is 8 ml.

I think I can use C1V1 = C2V2, but I am confused with the units.

Thanks.

-Mad Researcher-

To wok out the molarity you need to know the molecular mass of the solute. If you know this you can substitute this into the equation N = mass/molar mass to give you number of mol per volume. (hint - you know there are 50 mg in 1 ml.., just make sure you convert this to g or convert the g/mol unit for your chemical to keep the units consistent!)

Now, as you know C*V also equals N, so you can use this to your advantage...

N = C * V

N= 10 uM * 8

N= 80 uM  - this is the amount you want finally. From this you can also work

V= N/C

V= 80/ conc in uM of your solution.

-bob1-

bob1 on Sun May 6 02:15:30 2018 said:

To wok out the molarity you need to know the molecular mass of the solute. If you know this you can substitute this into the equation N = mass/molar mass to give you number of mol per volume. (hint - you know there are 50 mg in 1 ml.., just make sure you convert this to g or convert the g/mol unit for your chemical to keep the units consistent!)

Now, as you know C*V also equals N, so you can use this to your advantage...

N = C * V

N= 10 uM * 8

N= 80 uM  - this is the amount you want finally. From this you can also work

V= N/C

V= 80/ conc in uM of your solution.

Thanks for the explanation Bob. The Mol weight of the chemical is 234 g/mol

When you say N = mass/molar mass, do you mean 234/50?

-Mad Researcher-

Other way around: 50/234 (or rather 0.05g/234 g/mol)...

-bob1-

bob1 on Sun May 6 02:41:18 2018 said:

Other way around: 50/234 (or rather 0.05g/234 g/mol)...

So, I calculated like this -

0.05 g/ 234 g/mol = 0.0002 mol (is the unit correct).

N = C x V = 80 µM

V = N/C = 80/0.0002 = 400,000 (What would be the unit here?)

Is the overall calculation correct now?

-Mad Researcher-

One more unit conversion - you have the top correctly in mol, but remember this is for a 50 mg/ml solution so that 0.0002 is actually 0.0002 mol/ml,  The bottom is in micromol. Convert one or the other to get them to the same prefix - note that the 0.0002 is 0.2 mmol/ml and 80 umol is 0.08 mmol - if that helps keep it in some numbers that make sense. The final unit will be ml!

so V=N/C...

-bob1-

bob1 on Mon May 7 02:43:40 2018 said:

One more unit conversion - you have the top correctly in mol, but remember this is for a 50 mg/ml solution so that 0.0002 is actually 0.0002 mol/ml,  The bottom is in micromol. Convert one or the other to get them to the same prefix - note that the 0.0002 is 0.2 mmol/ml and 80 umol is 0.08 mmol - if that helps keep it in some numbers that make sense. The final unit will be ml!

so V=N/C...

Thanks, now it makes sense. The final answer is 0.4 ml or 400 µl.

-Mad Researcher-