4 replies to this topic

[rajah]

Hi you all!

Could you help me, please. What is the correct formula to make a molar solution of another solution which is not 100%. For example, how to make a 2M solution of ethanol 99%, Molecular weight 46,07g/mol?

Thanks alot for your help!

[rhombus]

rajah, on 23 November 2011 - 05:11 AM, said:

Hi you all!

Could you help me, please. What is the correct formula to make a molar solution of another solution which is not 100%. For example, how to make a 2M solution of ethanol 99%, Molecular weight 46,07g/mol?

Thanks alot for your help!

Dear Rajah,

A 99% ethanol solution is equivalent to 99g of ethanol in 100ml

Thus do the calculation:-

MW Ethanol =46.07

46.07g/L = 1M

99g/L = 2.07M

99g/100ml = 20.07M


To get a 2M solution dilute the stock (99%) by a factor of 1: 10.035 i.e. 1ml stock to 9.035 ml of water.

Esay really

Kindest regards

Uncle Rhombus

[ickypimp]

you assume ethanol has a density of 1g/ml, it does not... ethanol has a density of  0.789g/ml

[RajahII]

Hi again!

I find the first reply strange, I don´t understand it.

Could it be as simple as this:

calculate the mass (g) --> m=C*V*M
and the volume needed from this --> V=m/density 0,789

[doxorubicin]

The ethanol bottle will indicate whether 99% refers to w/w (weight/weight), w/v (weight/volume), or v/v (volume/volume).