50/50 IPA calculation

[sqeekykleen]

I picked up a bottle of 91% Isopropyl alcohol, (that was the only alcohol that they had), and want to make a mixture of 50/50. With this being higher % alcohol would I need to dilute with more water? What is the calculation? Thanks for the help.

[flyfishindawg]

I am pretty sure that this is the correct % to use for the 50/50 mix. This is what I use with good results.

[TOGWT]

With 70% strength isopropyl alcohol in order to obtain a 1:1 ratio (50/50 % mixture) use 2 parts alcohol to 1 part distilled water (See relevant sections for usage and dilution used.) Mix solution in a spray bottle, spray onto clean paint surface, and wipe off with a micro fibre towel.

[Blade]

Strictly speaking, just working out the math behind it...

With a 70% alcohol, you need a 2.5:1 mix ratio to achieve a 50/50 mix.
With a 91% alcohol, you need a 5:4 mix ratio to achieve a 50/50 mix.

[SweetJazz]

Hopefully this does not confuse anyone but the correct formula is as follows:

(70% IPA)( X amount of 70% IPA) = (50% IPA)(Total Volume of 50% Solution You Want To Make)

To make 1L of 50% IPA (Isopropyl Alcohol) using 70% IPA

(70% IPA) x ( X ) = (50% IPA) x (1L)

( X ) = (50% IPA) x (1L)
(70% IPA)

( X ) = 0.71L = 710mL = 710cc

So, to make 1L of 50% IPA you need 710mL of 70% IPA and 290mL of water. To make 0.5L just cut the volumes in half.

I purchased a cheap plastic 1L graduated cylinder from EBAY which makes this super easy to perform.

[67Customs]

I generally just use 91% straight. Works better and evaporates quicker.

[Blade]

So, to make 1L of 50% IPA you need 710mL of 70% IPA and 290mL of water. To make 0.5L just cut the volumes in half.
710ml:290ml ~ 2.45:1. I just rounded it to 2.5:1.