100% KOH Sap value chart

[Dave D]

Hello folks.
First time poster here.
I have a question so I figured I come to the experts.

I'm interested in finding a Sap chart that uses 100% pure KOH in it's listed values. Not one that is corrected for impurities that are commonly found in KOH. Does anyone know where one can be found online?

 

[Hertzyscowicz]

Some of the lye calculators let you choose to use KOH instead of NaOH.

Also, KOH weighs 56.1056 g/mol, and NaOH 39.99711 g/mol, so multiplying the NaOH weight by 1.4 gives you the right weight of pure KOH to use.

 

[Dave D]

Thanks for the speedy reply Hertzy.

I have found a few Sap charts online at soap making sites but the charts don't indicate if the quantities given have been changed to reflect less pure caustic since that's what we end up with.

I recall reading that some of the charts available have the Sap value elevated to reflect say 90% purity KOH.
Is this the case? Perhaps that's why there is a difference is Sap between some charts?
Does anyone know?

Just hoping to understand. Thanks for the input.

 

[agriffin]

I read that the impurity of KOH is anywhere from 7-15% or some range like that. So there is not a definitive value and therefore you'll find variations across different online calculators and references. I think most go with around 10%.

 

[Dave D]

I read that the impurity of KOH is anywhere from 7-15% or some range like that. So there is not a definitive value and therefore you'll find variations across different online calculators and references. I think most go with around 10%.

That makes sense.
When I'm performing a Sap value test I typically come out with around a 5-10% lower Sap value than the charts indicate (after accounting for impurities in the caustic).

Does anyone here titrate their caustic with an acid solution of known concentration to determine the purity?

 

[donniej]

I titrate with my oils. I'll hot process some oil and add caustic until no amount of cooking will bring the PH low enough to not trip phenolpthalien.

I keep meaning to pick up some muriatic acid from the hardware store as it's reliably 1/3 pure HCL. So by dilluting 1 part caustic with 2 parts water, it should be easy to titrate.

 

[Dave D]

I titrate with my oils. I'll hot process some oil and add caustic until no amount of cooking will bring the PH low enough to not trip phenolpthalien.

I keep meaning to pick up some muriatic acid from the hardware store as it's reliably 1/3 pure HCL. So by dilluting 1 part caustic with 2 parts water, it should be easy to titrate.

I'm not sure I'm following you on what that will tell you. Can you explain further?
I have a rather fair knowledge of analytical chemistry, (as I'm sure others here do as well) perhaps I can help work out something if you're interested.

 

[donniej]

Cook up some of your oil, slowly adding your caustic..... cooking.......cooking..........cooking........ when it stops reacting, swab the batch with a Q-tip and test with phenolpthalien (hereafter called phenol). It shouldn't trigger the phenol, if it does then you didn't cook it enough. Add a small measured amount more of caustic and keep cooking. Check again with phenol. When you can't get it to a ph low enough that it doesn't trigger the phenol then you've achieved full sap.

This is a titration but you need to cook it over a longer period because of the rate at which the oils react. It's just a titration, nothing more.

PS. if you try this be sure to keep adding water. If you run low or out of water, the process stops. It's easy to do when cooking it for hours.

 

[Dave D]

Cook up some of your oil, slowly adding your caustic..... cooking.......cooking..........cooking........ when it stops reacting, swab the batch with a Q-tip and test with phenolpthalien (hereafter called phenol). It shouldn't trigger the phenol, if it does then you didn't cook it enough. Add a small measured amount more of caustic and keep cooking. Check again with phenol. When you can't get it to a ph low enough that it doesn't trigger the phenol then you've achieved full sap.

This is a titration but you need to cook it over a longer period because of the rate at which the oils react. It's just a titration, nothing more.

PS. if you try this be sure to keep adding water. If you run low or out of water, the process stops. It's easy to do when cooking it for hours.

I see what you mean in regards to determining how much caustic to use based on utilizing phenolpthalein indicator.

The part I was unsure of was the 1/3 HCl and 1:3 caustic to water ratio.

When I'm performing a sap test I use Isopropol alcohol instead of water, combined with about 50g of fat sample, and add about 5-10% more caustic than it's estimated to take. After cooking for an hour draw out a sample of 1-5g of saponified sample and titrate it using a .1N HCl solution with phenolpthalein indicator. The amount of .1N solution is in direct relation to the amount of residual caustic left over following saponification.

 

[donniej]

The muriatic acid sold at hardware stores is 33% HCL in water. It's cheap, easy to get and is of a reliable purity. I was suggesting using this to titrate your caustic because of the fore-mentioned reasons. You know the deal, just dillute 1 part NaOH or KOH with 2 parts water. Equal parts of each solution should nuetralize both.

This is much nicer than trying it with 98% H2SO4 and lye flakes. My kitchen counter will never be the same (just kidding)

 

[Dave D]

The muriatic acid sold at hardware stores is 33% HCL in water. It's cheap, easy to get and is of a reliable purity. I was suggesting using this to titrate your caustic because of the fore-mentioned reasons. You know the deal, just dillute 1 part NaOH or KOH with 2 parts water. Equal parts of each solution should nuetralize both.

That's not quite how it works.
1g of 100% KOH = 2.07g of 31.45% muriatic acid.
I used 31.45% as opposed to 33% since that's what we commonly get around here in VA.

1g KOH contains .0178mol OH
1g of 31.45% muriatic contains .3145g HCl
.3145g HCl contains .0086mol H
.0178mol,g / .0086mol,g = 2.07g

 

[donniej]

I see you've done this before

I wrote that down and will try it next time I can get some more muriatic acid. I never though about the need to convert to moles but I completely agree with your numbers.

What do you do that you use that level of chemistry?

Thank you!

 

[Dave D]

I see you've done this before

First time here

What do you do that you use that level of chemistry?

chemistry

Thank you!

No problem.
I'm here to learn about soaping as an art and aid in what ever way I can. I know alot about the chemistry side of tall oils but the artsy side of soaping is what I would like to know more about.
Hopefully you guys and gals can educate me and I can donate what information I can.