You have 10 ml of ethanol and want to use it all to make a 10-fold dilution with water. how would you do this, including the final volume? show your calculations and give complete instructions.

You should add water to the 10 ml ethanol until you have a 100-ml solution. For this, pour the 10 ml ethanol in a 100-ml volumetric flask and add water until the mark that indicates that you have a volume of 100 ml. Don´t forget to mix before you reach the mark.

Explanation:

You can assume that your ethanol has a concentration of 1X.

if you have to dilute it ten times, the final concentration will be 1X / 10 = 0.1X

The number of moles of ethanol present in the solution will remain the same after the dilution because you are not adding nor substracting ethanol, that means:

mol ethanol before dilution = mol ethanol after dilution

The number of moles can be expressed in this form:

mol ethanol = volume of the solution * concentration of ethanol

then, to find how much water you have to add you have  to solve the final volume (Vf) from this equation:

mol ethanol before dilution = mol ethanol after dilution

               Vi * Ci                 =             Vf * Cf

where:

Vi = volume of the solution before dilution.

Ci = concentration of the solution before dilution

Vf = volume of the final solution

Cf = concentration of the final solution

Replacing with the data:

10 ml * 1X = Vf * 0.1X

10 ml *1X / 0.1X = Vf

100 ml = Vf

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