water to lye ratio

[Soapman Ryan]

What is the minimum water to lye ratio to melt NaOH or KOH?
Some where I read water to NaOH is 1:1, is this correct and what is the min. for KOH?
Thanks

 

[MorpheusPA]

http://en.wikipedia.org/wiki/Potassium_hydroxide#Solubility_and_desiccating_properties

The same 1:1 ratio is fine; KOH is slightly less soluble in water than NaOH counting by number of molecules, but more grams of KOH dissolve in the same grams of water than NaOH due to the lighter molecular weight.

Please note that a 1:1 solution of either will be very strong, so exercise all due caution when handling it.

 

[Soapman Ryan]

http://en.wikipedia.org/wiki/Potassium_hydroxide#Solubility_and_desiccating_properties

The same 1:1 ratio is fine; KOH is slightly less soluble in water than NaOH counting by number of molecules, but more grams of KOH dissolve in the same grams of water than NaOH due to the lighter molecular weight.

Please note that a 1:1 solution of either will be very strong, so exercise all due caution when handling it.

Thanks, for the wikipedia page you suggested.
I see KOH would be 1.21:1 KOH:WATER ratio.

"Approximately 121 g of KOH will dissolve in 100 mL of water at room temperature"

 

[MorpheusPA]

Thanks, for the wikipedia page you suggested.
I see KOH would be 1.21:1 KOH:WATER ratio.

"Approximately 121 g of KOH will dissolve in 100 mL of water at room temperature"

1 g to 1 ml would be far safer. Depending on the temperature of the water, you'd risk not having all of the KOH dissolve, or risk some precipitating out if water temperatures fall under seventy.

I've never agreed with 1:1 for NaOH for exactly that reason and wouldn't dream of going under about 1.2:1 water/NaOH.

 

[Soapman Ryan]

1 g to 1 ml would be far safer. Depending on the temperature of the water, you'd risk not having all of the KOH dissolve, or risk some precipitating out if water temperatures fall under seventy.

I've never agreed with 1:1 for NaOH for exactly that reason and wouldn't dream of going under about 1.2:1 water/NaOH.

I'm working on calculations at 1.5:1, would that be safe to say all the KOH would dissolve?

 

[MorpheusPA]

I'm working on calculations at 1.5:1, would that be safe to say all the KOH would dissolve?

1.5 water: 1 KOH lye? Yes, all the lye should dissolve unless the water is just a whisper above freezing. Since the water warms as the lye dissolves, that will also help.

I suppose one question others will ask (I tend to evaluate on the chemistry alone without consideration) is why the sharp discount?

 

[Soapman Ryan]

1.5 water: 1 KOH lye? Yes, all the lye should dissolve unless the water is just a whisper above freezing. Since the water warms as the lye dissolves, that will also help.

I suppose one question others will ask (I tend to evaluate on the chemistry alone without consideration) is why the sharp discount?

I'm working on a new shave soap (hot process) and was hoping with the lesser amount of water I won't have to let it "cook" in the crockpot for an hour. Is this true would, would it be done faster @ 20-30min instead of 1 hour?

 

[DeeAnna]

HP usually has more water than CP simply for processing -- it has to be fluid enough so you can stir it for best results.

The rate of saponification is partly related to the concentration of the lye, yes, but the overall temperature of the batter, the type of fatty acids in the recipe, the degree of mixing, and other issues affect the reaction rate too. I honestly doubt you're going to cut the saponification time in half just by reducing the lye concentration.

Honestly my shave soap doesn't need an hour long cook even at a relatively low 25% lye concentration ... 15 minutes is all it really needs ... and I can mix it if I use a sturdy spatula and some elbow grease. I'd hate to see what the batter would be like to mix if I used a 50% lye concentration so the batter had only one third the water!

 

[Soapman Ryan]

HP usually has more water than CP simply for processing -- it has to be fluid enough so you can stir it for best results.

The rate of saponification is partly related to the concentration of the lye, yes, but the overall temperature of the batter, the type of fatty acids in the recipe, the degree of mixing, and other issues affect the reaction rate too. I honestly doubt you're going to cut the saponification time in half just by reducing the lye concentration.

Honestly my shave soap doesn't need an hour long cook even at a relatively low 25% lye concentration ... 15 minutes is all it really needs ... and I can mix it if I use a sturdy spatula and some elbow grease. I'd hate to see what the batter would be like to mix if I used a 50% lye concentration so the batter had only one third the water!

That's good to know. Currently I've been using the 25% lye concentration as you mentioned in another post. Maybe I'll stay with that and give it a shorter cook. I was thinking if it didn't get completely saponified, like when emulsifying CP soap, during its 5 month cure time it would finish curing.