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Basic general formula for making solutions?

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#1 rajah

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Posted 23 November 2011 - 05:11 AM

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!

#2 rhombus

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Posted 01 December 2011 - 04:14 AM

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

#3 ickypimp

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Posted 02 February 2012 - 06:23 PM

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

#4 RajahII

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Posted 06 February 2012 - 05:45 AM

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

#5 doxorubicin

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Posted 07 February 2012 - 10:34 PM

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