Help with Citric Acid Math! Please!

[pmartin]

I have horrible hard water and want to add citric acid to my shave soap. Im terrible at math. I've read and re read DeAnna's Classic Bells tutorial and think I have it right.

Would someone be kind enough to check my figures pretty please?

I want to use 2% Citric Acid.

Total oil weight - 425 grams
2% of total oil weight is 8.5 grams

Dual lye solution is KOH 62 grams and NaOH 11 grams. So I need to figure the extra NaOH to add back in.

8.5 x 6.24 / 10 = 5.34 grams of added NaOH?

Is this correct? I think I've messed up somewhere since according to my calculations I'm adding almost half the total extra NaOH the recipe calls for.

Also to clarify, since its dual lye I only need to calculate for the NaOH portion and not the KOH, correct?

 

[DeeAnna]

That looks right. And yes I suggest just adding enough extra NaOH to neutralize the citric acid for a dual lye recipe. There's no need to fiddle with adding extra KOH.

 

[pmartin]

Thank you So much DeeAnna!

 

[penelopejane]

I don't think your KOH and NaOH numbers look right. Are you using 95% NaOH and 5% KOH? Your KOH is higher. Or have you just transposed them?

I use 1% and it makes a noticeable difference. Maybe you could test both percentages. If you use too much you get crystals on your soap.

 

[DeeAnna]

Penelopejane -- The OP is making shave soap, so the OP might not be using the usual 95% NaOH and 5% KOH that's typical for bar soap. It's fine to use this method on any dual lye soap recipe.

 

[SudsanSoaps]

Should be 5.304 grams instead of 5.34 but doesn't make any real difference.

 

[Skatergirl46]

There is a lye calculator called Soapee that can calculate dual lye soaps. It’s free too.

 

[DeeAnna]

Can you use Soapee to calculate the extra NaOH needed for citric acid?

 

[Chispa]

Can you use Soapee to calculate the extra NaOH needed for citric acid?

No, you still need to calculate additional lye for CA manually. It's probably better that way, so that adding additional lye is a deliberate action, and difficult to arrive at a lye heavy soap by accident.

I've noticed a huge difference between 1% and 2% CA additions to my soap. My 2% CA soap with no coconut oil vastly outperforms my 1% CA soap with 15% CO in terms of lather. The other ingredients are 5% Castor oil and the balance lard.

The joys of having hard water!

 

[DeeAnna]

"...No, you still need to calculate additional lye for CA manually...."

Thank you! I don't use the online soap recipe calcs to create my recipes, but I was thinking Soapee wasn't any better than the others on this point. I get your point about doing the calculation manually, but not everyone is comfortable with the math required. We get a lot of questions, such as this one. It sure would be nice for a calc to offer an "add an acid" option for the math challenged.

 

[neonstudy]

Calculation looks right. I've only tried 0.5% citric before, let me know how the 2% goes.

 

[DeeAnna]

Many people use citric acid in the 2% range. There aren't any "here be dragons" problems to worry about. I think Carolyn (cmzaha) has used it at 3%, but if I recall correctly she says it can crystallize out on the surface of the soap at that dosage. But anything less than that is fine.

At 0.5% the sodium citrate is protecting your soap against rancidity (DOS, dreaded orange spots) caused by metal ions, but that probably isn't enough to prevent soap scum unless your water is very very soft. A dose of 2% to 3% will be more effective against soap scum as well as rancidity.