abv query

[CW101]

Hi there,

I could do with a little help please.

I have a litre of liquid at 40% abv

If I add 1 litre of water in theory the abv should drop to 20% or there abouts

My calculation for this is 40/(1 + 1) = 20

However if I have 2 litres of liquid at 40% abv and I apply the same calculation I get an abv of 13.33% which has to be wrong as I have more liquid at 40%.

There must be an error in my 1st calculation.

Can anyone advise me please?

CW

 

[bucketnative]

You need to account for volumetric fraction of each solution in your calculation.

You have two concentrations:

C1 = 40% ABV
C2 = 0% ABV

You have two volumes

V1 = 2 Liter
V2 = 1 Liter

Find the volumetric fraction of each solution:

X1 = V1/(V1+V2) = 2/3 = 0.67
X2 = V2/(V1+V2) = 1/3 = 0.33

Then, find the final concentration, Cf, after mixing:

Cf = X1*C1 + X2*C2 = (0.67*40%) + (0.33*0%) = 26.7% ABV

 

[madscientist451]

Just use the dilution calculator, to determine how much water to add:

http://homedistiller.org/distill/dilute/calc

note the above calculator is from a home distillation page, and discussion of distillation is a violation of HBT rules. Apologies in advance are given to anyone who feels copying and pasting a dilution calculator here is in bad taste, offensive, illegal or otherwise violates sensibilities.

 

[KeyWestBrewing]

I believe this is what your looking for its for calculating the ABV of cocktails/mixed drinks.

(volume of liquor x alcohol by volume/total cocktail volume) x 100

 

[GuldTuborg]

Bucketnative has the right of it. Your original math did not represent the alcohol concentration of each respective liquid. It just happened to give the right result in the first instance, even though the method was wrong.

 

[CW101]

Many thanks - I see where I was going wrong

CW