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Ammonium hydroxide in soap

Sodium hydroxide (NaOH) and potassium hydroxide (KOH) are the two most common alkalies for making soap, but they are not the only options. Ammonium hydroxide solution (ammonia solution) is another alkali that can be used to make soap.


Why would a person want to use ammonia solution in soap?

Soap made with ammonium hydroxide (NH4OH) solution is slightly more water soluble than soap made with potassium hydroxide. It is even more soluble compared with soap made with sodium hydroxide.

Household ammonia solution (5% NH4OH in water) is used in some older soap recipes, especially ones for lard-based household cleaning and laundry soaps. Lard makes a fairly insoluble soap, so adding some ammonia solution will help this type of soap dissolve faster and lather more easily.


What are the pros and cons of ammonia solution versus KOH?

Both alkalis offer the same benefits of helping soap to dissolve faster and lather more easily. They will be especially useful for soaps high in palmitic and stearic acid to increase the solubility and when making soaps high in oleic acid to reduce the castile "slime."

KOH is seldom sold locally; it usually has to be special ordered and shipped. For high volume use, KOH may be more cost effective since it can be purchased in bulk.

Household ammonia solution is readily available in local grocery and hardware stores, at least in the US. Ammonia solution can be purchased in small quantities and may be more convenient for hobby/home soap making.

KOH can be used as the sole alkali to make shave soap or liquid soap. It can be blended with NaOH to make a "dual lye" solution for making cream, shave, or bar soap.

Ammonia solution is not concentrated enough to be the only alkali in a soap; it must always be combined with KOH or NaOH.

After a KOH (or NaOH) solution has cooled to room temperature, the gas above the solution is only air and water vapor. There will essentially be no alkali in this air, so there is no need for extra ventilation or respiratory protection.

Even at room temperature, the gas above an ammonia solution will always contain some ammonia gas, a strong respiratory and eye irritant.


What is ammonium hydroxide solution?

Ammonium hydroxide (NH4OH) solution is ammonia gas dissolved in water. Pure ammonia (NH3) is an extremely hazardous gas and cannot be safely handled without proper training and equipment. Ammonium hydroxide solution is the only reasonably safe ammonia product that soapers should use.

The easiest kind of ammonium hydroxide solution to find is "household ammonia," a cleaning product sold in many grocery and hardware stores (at least in the US.) It typically contains about 5% ammonium hydroxide by weight. Stronger ammonia solutions are sold for commercial cleaning and laboratory work, but these products are not covered in this article.

Some household ammonia solutions contain added soap (cloudy, sudsy, or soapy ammonia solution) and some are plain (clear ammonia solution). Either version may contain fragrance. I recommend using plain, not-fragranced ammonia solution for making soap.


What are the safety concerns about 5% ammonia solution?

Even though 5% ammonia solution is sold to consumers as a cleaning product, it is normally not used full strength for regular household cleaning. You will be working with the full-strength solution, so use extra care when working with this product.

Ammonium hydroxide has a pungent, irritating odor. It will irritate and burn the eyes, nose, lungs, and skin. Use good ventilation when working with ammonia solution, and wear the same safety gear you normally use when working with NaOH and KOH.

The hazards are lower after the soap is safely saponifying in the mold, but I recommend putting the mold in a well ventilated area away from spaces where people are present, especially children, pets, or people with respiratory problems.

After ammonia is fully converted into soap, there should be no lingering ammonia odor.


How much 5% ammonia solution should I use in soap?

Because household ammonia solution is mostly (95%) water, use it as a partial to full replacement for the water-based liquid in your soap recipe.

You must also reduce the NaOH (or KOH) in your recipe to compensate for the added NH4OH. If you do not make this adjustment, your soap will contain less superfat than you want, and it may even be lye heavy.

1 gram of 5% household ammonia solution is equivalent to 0.044 grams of NaOH

1 gram of NaOH is equivalent to 22.829 grams of 5% household ammonia solution


How should I adjust my soap recipe?

1. Prepare your soap recipe using the soap calculator you like best. Choose NaOH as the alkali (lye) for the recipe. If you have not yet used a soap recipe calculator, Soapee is a good calc to use.

2. Decide how much 5% ammonia solution you want to use. Always measure in grams or ounces (that is ounces by weight, not volume). You can choose any amount of ammonia solution up to a full replacement of the water calculated for the recipe.

To replace all of the water in your soap recipe with 5% ammonia solution, you should use a bit more ammonia solution because it is only 95% water --

Total ammonia solution = Calculated total water X 100 / 95

To use less ammonia solution than a full water replacement, just decide on the weight you want and skip this calculation.

3. Calculate how much water is in the 5% ammonia solution --

Water in ammonia solution = Total ammonia solution X 95 / 100

4. Subtract this water from the total water amount calculated for the recipe. The answer how much extra water you will need to add --

Extra water to add = Calculated total water - Water in ammonia solution

If you are doing a full water replacement, this answer should be zero (see Example 1.)

5. Recalculate the total NaOH weight to allow for the NH4OH added by the 5% ammonia solution --

NaOH to add = Calculated NaOH - (Total ammonia solution / 22.829)

Math tip: Do the division problem FIRST (Total ammonia solution / 22.829) and then subtract that answer from the Calculated NaOH weight.


Example 1.

My soap recipe calls for 254 grams of water and 225 grams of NaOH without any added ammonia solution.

I want to adapt this recipe to use 5% ammonia solution as a full replacement for the water.

Total ammonia solution = 254 X 100 / 95 = 267.4 grams

Water in ammonia solution = 267.4 X 95 / 100 = 254 g

Extra water to add = 254 - 254 = 0 g

NaOH to add = 225 - (267.4 / 22.829) = 225 - 11.713 = 213.3 g


Example 2.

My soap recipe calls for 254 grams of water and 225 grams of NaOH without any added ammonia solution.

I want to adapt this recipe to use 175 grams of 5% ammonia solution.

Total ammonia solution = 175 grams

Water in ammonia solution = 175 X 95 / 100 = 166.3 g

Extra water to add = 254 - 166.3 = 87.7 g

NaOH to add = 225 - (175 / 22.829) = 225 - 7.666 = 217.3 g


How should I add ammonia solution to my soap?

Measure the weight of 5% ammonia solution needed for your recipe and mix it with any additional water needed. Stir the other alkali (NaOH and/or KOH) slowly into this mixture as you would normally do to make a lye solution. Proceed to make soap as usual.


More discussion about ammonia solution



Extra credit: How do you convert an NaOH weight into the correct weight of pure NH4OH (or KOH)?

Ammonia (more correctly: ammonium hydroxide) is NH4OH. Sodium hydroxide is NaOH. One molecule of ammonium hydroxide will make one molecule of soap. Ditto for sodium hydroxide.

Here are the basic "stochiometric" equations for these two soap-making chemical reactions:

1 molecule of fat + 3 molecules of NaOH => 3 molecules sodium soap + 1 molecule glycerin

1 molecule of fat + 3 molecules of NH4OH => 3 molecules ammonium soap + 1 molecule glycerin

1 molecule of fat + 3 molecules of KOH => 3 molecules potassium soap + 1 molecule glycerin

Notice the numbers are the same in each equation -- ONE molecule fat, THREE molecules of lye, etc.? That means 1 molecule of any of these alkalis will do the same job when making soap.

A little more chemistry information is needed --

NaOH molecular weight = 40 grams per 1 mole

NH4OH mol wt = 35 grams per 1 mole

KOH mol wt = 56.1056 grams per 1 mole

Why did I jump from talking about individual molecules to talking about "moles"? What's a mole?

In this context, a mole isn't a furry underground animal. It is a name chemists use to mean a specific number of molecules. A "dozen" means 12 doughnuts, a "gross" means 12 dozen (144) pastries, and a "mole" means 624,000,000,000,000,000,000,000 molecules.

To substitute pure NH4OH for NaOH, we would convert the NaOH weight like this --

Weight NH4OH = Grams NaOH x Mol wt NH4OH / Mol wt NaOH

Let's assume a soap recipe needs 100 g of NaOH to saponify some fat.

Weight NH4OH = 100 grams NaOH x 35 g NH4OH/mole / 40 g NaOH/mole

= 87.5 g of NH4OH would be needed to do the same job

We need less WEIGHT of NH4OH, but that weight still gives us the correct number of NH4OH MOLECULES to convert that fat into soap.

This same method can be used to find the weight conversion between NaOH and KOH. Just substitute the molecular weight of KOH in place of the NH4OH molecular weight.

Here are the conversion factors for the alkalis most often used in soap making --

1 gram of NaOH is equivalent to 35/40 = 0.875 grams of pure NH4OH

1 gram of NaOH is equivalent to 56.1056/40 = 1.403 grams of KOH

The other thing to remember is we can't use pure, concentrated NH4OH to make soap. We have to use a diluted ammonia solution. To get information that is practical for soap making, you have to convert the weight of pure NH4OH into a weight of diluted ammonia solution. Household ammonia solution is usually about 5% pure NH4OH by weight. The weight of household ammonia solution can be calculated from the amount of pure NH4OH in this way --

Weight 5% NH4OH solution = Weight pure NH4OH / 5 X 100 = 20 X Weight pure NH4OH

In other words, if you want to use household 5% ammonia solution, you have to use a LOT more ammonia solution (20 times more!) than the amount of pure NH4OH.