# How to make 25% acid from 85%

Expecting my order from dudadiesel (thanks to someone here who posted link) of food grade 85% phosphoric acid. Although I do have a nice pipette and pump for measuring minute quantities of acid I would prefer diluting the acid so the measurements are more forgiving. Seemed like an easy thing to do at first, but how the heck do I dilute the 85% concentration to get a 25% solution or something close with some level of accuracy? Thanks in advance!

This sounds like too much math for me but I’m just curious as to what you’re planning on doing with phosphoric acid.

The numbers don’t work out very pretty, but I believe you need 12 parts water to 5 parts of your 85% solution.

(5 parts x 85% / 17 parts = 25 %)

I’d let someone else confirm this before your proceed.

I would just go one part acid to three parts water and get something around a 25% solution.

Mpls, it is used to acidify your mash or sparge.
I have always chosen phosphoric over lactic. It has been long discussed in the same vein as lactic. As a matter of fact De Clerk advocates its use because it is more neutral and safe to handle as opposed to lactic, hydrochloric, citric etc…which all have some type of negative aspect. Whereas phosphoric has no detriment at all. Some say at low dose lactic, sauermalt or sauergut imparts no flavor impacts but I find it simple to avoid lactic altogether for an assured promise of clean/ neutral impacts throughout my process.

The formula for dilutions is: C1 x V1 = C2 x V2

C1 is 85
C2 is 25
Assume that you want 1 liter of final 25% solution (V2)

Solving that equation gives V1 = (C2xV2)/C1

So V1 is 0.294 liters.

Add 0.294 liters of 85% phosphoric to 0.706 liters of distilled water to create 1 Liter of 25% solution

The volumes above can be adjusted as to whatever units, gallons, pints, mL, etc.

If you don’t have an accurate way to measure volume, you can use a good scale to measure out the 85% phosphoric. Its density is 1685 grams per liter.

Thanks guys.

Itspossible, thought I was the only one that was “sensitive” to lactic acid. Couldn’t agree more. When I see guys say they can’t taste 3ml in 5G, I think that’s crazy. Lactic acid/sauergut have their place in german styles but a little goes a long way. I am beginning to wonder if german brewers even use sauergut/malt in hefes/weissbier? I don’t detect a hint of it in commercial examples…

Martin, thanks for the calculations. Exactly what I needed. On another note, I finally took the time to use Bru’n water and it was well worth it. Nice spreadsheet there. pH meter electrode broke so I am going to use it for next batch until replacement is here… Also, If you would be kind enough to comment, I read some posts I believe you wrote relating to nano filtration. Are brewers you consult with interested in completely removing bicarbs or just removing enough to make pH adjustments easier?

[quote=“mabrungard”]The formula for dilutions is: C1 x V1 = C2 x V2[/quote]Don’t you need to take into account the weight of the acid in solution?

Density of 85% phos = 1.69 g/mL
Density of 25% phos = 1.15 g/mL
Density of water = 1.0 g/mL

Assuming 100mL of 85%, and with “X” as the volume of water to add, you set up the equation: [(100 * 1.69) + (X * 1.0)] = [(100+X)*(1.15)] and solve for X, which gives you X = 360mL.

So for one liter of 25% phos, you would need [1000/(360+100)]*360 = 782 mL of water to which you will add (1000-782) = 218 ml of 85% phos.

No, the weight or specific gravity of the solution does not enter in to this calculation. Read here: http://water.me.vccs.edu/courses/env211/lesson8_4.htm

There are plenty of dilution calculators on the web. Google it.

[quote=“mabrungard”]There are plenty of dilution calculators on the web. Google it.[/quote]That’s too easy! It’s more fun to try to dredge up classwork from 20 years ago and make it more complicated. And get the wrong answer, too. Of course, the PE I asked to look over my work didn’t have a clue, so that shows you what happens when you don’t use the info for a couple of decades.