How to prepare 70% Ethanol?

2 Replies

To prepare 70% Ethanol from a 95% Ethanol,

Calculate using dilution equation M1V1 = M2V2

Stock solution= Diluted solution

M1= molarity of the stock solution

M2= molarity of the diluted solution

V1= volume of stock solution

V2= volume of diluted solution

For 100ml of 70% Ethanol,

0.95 x V1 = 0.7 x 100ml

V1 = 73.68ml

 

Trick 1:

Take 70 ml of 95% Ethanol and add water to 95 ml.

(0.95 x 70ml = 0.7 x 95ml)

Take 350ml of 95% Ethanol and add water to 475ml.

(70ml x 5)

Trick 2:

Take 300ml of 95% Ethanol and add 100ml of water, which give you 400ml of 70% Ethanol (71.25%) (in 3:1 ratio)

Take 295ml of 95% Ethanol and add 105ml of water, which give you 400ml of 70% Ethanol (70.06%)

2 thoughts on “How to prepare 70% Ethanol?”

  1. Doug

    Trick 2 does not work, since adding 300mL 95% ethanol to 100mL water does not equal 400mL. The final volume is actually less than 400mL, as the water and ethanol molecules fit tighter and he

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