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# Make up dilutions (mg/cm3) watch

1. I have been given a stock solution at concentration 4 mg/cm3.

From this solution I have to prepare dilutions, containing 3, 2, 1 and 0.5 mg/cm3 in a 5cm3 volumetric flask.

Does anyone know how to work out how much volume I am to use for each one?

Thanks.
2. may I ask what the solution is? and how much you have?

You could probably use conc.=(moles*mr)/(vol.) in g/cm3 and add something to increase the volume. cant remember what you should add... (if it comes to mind I will say.)
3. solution is 2-methly-2-nitrosopropane in heptane.
I have not been given any amount.

thanks
4. (Original post by lbc1809)
solution is 2-methly-2-nitrosopropane in heptane.
I have not been given any amount.

thanks
Just thinking...

get a set amount... then you have the original c=m/v so you can get moles of solution. (you have conc and volume) and then find the Mr of 2-methly-2-nitrosopropane and heptane.. and then you can use

conc = moles * mr / vol.

and insert your conc you want ie 3, and as you have moles*mr from before you can find out what the volume needs to be and add something to increase the volume (distilled water maybe) ??

just my 2 pence... hopefully a chemist will come along and confirm this, or reject it

but hmm you don't have the 2methyl.... and heptane ratio.... so I dont know if that would work...

================================ ================================ ================

thinking more basic... starting from 2 cm^3 of the 4mg/cm^3 solution and

add 2.67cm^3 distilled water to get 3mg/cm^3 (2:2.67) (2.14:2.86)

add 2cm^3 to get 2mg/cm^3 (1:1) (2.5:2.5)

adding 4cm^3 to get 1mg/cm^3 (1:2) (1.67:3.34)

adding 8cm^3 to get 0.5mg/cm^3 (1:3) (1.25:3.75)

in those ratios (oringinal solution : distilled water) [[[(amount of original in cm^3 : amount of water in cm^3)- to get it into 5cm^3]]]

Maybe?
5. It's the same as if you were working with units of mol dm-3. It's just that you're using a weight/volume concentration instead.

For the 2 mg/cm3 you need to halve the original concentration. Therefore in a 5 cm3 volumetric flask you'll use 2.5 cm3 of stock solution and then make it up to the mark with your solvent.

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