Another master-batching question

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sudsy_kiwi

Well-Known Member
Does anyone know how much volume dissolved lye adds to water?

Ie, I know that putting a kilo of NaOH into a kilo of H2O will give me 2 kilos of solution...but how much space will that occupy?

I ask because I've just bought 5kg of lye and want to master-batch it. I have a 5L (safe) plastic bottle to store it in. My first thought was 2.5L (ie 2.5kg) of water with 2.5kg of lye, but quickly realised that that will not fill the bottle. I want to make up as much as I can fit into the bottle, without wasting any solution, or space.

Hope that makes sense

cmzaha

Supporting Member
If you are planning on masterbatching the entire 11 lbs of lye you need a container that can withstand the heat. 11 lbs of 50/50 lye solution is going to produce a lot of heat. Also put your container in an ice batch. I master batch approx 8 lbs at a time and my hdpe buckets hold up but I can feel them soften. I also mix in the since in an ice bath

topofmurrayhill

It should be a little over 1.5 times the density of water.

The 5 l bottle will hold 7.5 kg lye.

That would be 3.75 kg water and 3.75 kg NaOH.

However, the volume will be greater when the lye is hot. This calculation has a little wiggle room in it, but probably wouldn't work when the lye is freshly mixed. It should be good if it's around 100 F or 40 C or cooler, but you probably couldn't mix it in the bottle without overflowing.

If you want to mix in the bottle it's more like 3.675 kg caustic. Let's say 3.5 to be safe.

Last edited:

DeeAnna

Well-Known Member
A 50% NaOH solution has a specific gravity (SpGr) of 1.53 at 16 C (60 F). The specific gravity will change with concentration and with temperature.

I'm just going to leap over some background info and simply say for this to work properly, you must use milliliters (mL) and grams (g). If you want the reasoning, I'll be happy to explain, but let's leave it for later.

The math relationship between weight, specific gravity, and volume is this:
Volume NaOH solution = (Weight NaOH solution) / SpGr

You can turn this relationship around to find the weight, given the volume:
Weight NaOH solution = (Volume NaOH solution) X SpGr

Examples:

How much does 1000 mL of 50% lye solution weigh?
Wt = Vol X SpGr = 1000 mL X 1.53 = 1530 grams
What this is telling you is a given volume of 50% NaOH solution weighs a LOT more than the same volume of water.

How much volume does a mixture of 2000 g NaOH and 2000 g water have?
Total weight = 2000 g NaOH + 2000 g water = 4000 g
Vol = Wt / SpGr = 4000 g / 1.53 = 2614.4 mL

Other specific gravity numbers for NaOH and water mixtures at 60 F:

25% NaOH => 1.278
30% NaOH => 1.332
33% NaOH => 1.363
40% NaOH => 1.434
45% NaOH => 1.483
50% NaOH => 1.530

sudsy_kiwi

Well-Known Member
Thank you for your help. DeeAnna, that is perfect, thanks.

I was aware the density would change and therefore the relationship between volume & weight, but not by how much. I'll be printing that post out and adding it to my knowledge bank

Also, yes I will be mixing it in a different (also safe) bucket, then transferring it to the bottle for storage. Th ebottle will then be stored in another, securely lidded' bucket. I've felt the heat that comes from mixing ~200g of lye...don't want to subject my bucket to the results of 10x that amount of lye lol

DeeAnna

Well-Known Member
I think you're confusing temperature with energy. 200 g of 50% NaOH solution will initially heat up to about the same temp as 2000 grams or 20,000 grams of the same solution at the time of initial mixing.

What's different is that cooling a larger amount of lye solution takes a lot more work and time than cooling a smaller amount, all other things being equal, so that's where a sturdy container and a water bath with lots of ice come in handy.

dixiedragon

Well-Known Member
What Deanna said. Keep in mind that surface area increases by square inches (or centimeters) but volume increases cubically. So if you use the same pitcher to make 1 cup or 10 cups of lye water, the 10 cup batch has significantly less surface area (proportionally) for the heat to escape from.

cmzaha

Supporting Member
I think you're confusing temperature with energy. 200 g of 50% NaOH solution will initially heat up to about the same temp as 2000 grams or 20,000 grams of the same solution at the time of initial mixing.

What's different is that cooling a larger amount of lye solution takes a lot more work and time than cooling a smaller amount, all other things being equal, so that's where a sturdy container and a water bath with lots of ice come in handy.
I definitely stated it wrong. It just takes so long to cool down such a large batch even in an ice batch that hdpe bucket will soften, and an ice bath is imperative in my opinion. Thankyou for the correction DeeAnna. Scientific I am not, Hands on I am

houseofwool

Well-Known Member
I frequently make a 50:50 solution in a 5 gallon bucket that my coconut oil came in. In the winter I set in a snow drift to cool. The other day it melted through 8" of snow down to the ground!

cmzaha

Supporting Member
I frequently make a 50:50 solution in a 5 gallon bucket that my coconut oil came in. In the winter I set in a snow drift to cool. The other day it melted through 8" of snow down to the ground!
Wow, what a neat way to cool it down.

The Efficacious Gentleman

And a great way to clear the driveway of snow!

houseofwool

Well-Known Member
I am lazy and the snow is free!