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A study of saponification reactions

A study of saponification reactions

Introduction: (Initial Observation)

Soap has played an important part in human history and has long been part of civilization. Even though it has been around for thousands of years it has only been within the past 200 years that it has been widely used to clean the human body.
Saponification is the process of making soap by reacting a strong base and a fat.

Soaps also include products that are not generally known as soaps. Shaving creams, greases and many industrial lubricants for example are made using the same process of saponification.

Based on the reports of US census bureau in 1997, about 60000 workers have been employed by about 2000 soaps and detergents manufacturing companies in United States.

This project is in two parts:

In part 1 you make soaps using simple traditional methods in order to make yourself familiar with soap making techniques and related chemical processes.

In part 2 you will study the effects of one specific factor in the soap quality. Following is a list of some sample questions that you may choose from.

  1. Can soap be made from stearic acid (or other fatty acids) instead of animal fat? (Exp. 1)
  2. How does the choice of fat affect the properties of the soap? (Exp. 2)
  3. pH of the soap affect the foaming ability of the soap?
  4. How does the type of fat affect the cleaning ability of the soap?
  5. How does the type of base affect the hardness/ softness of the soap?


This project guide contains information that you need in order to start your project. If you have any questions or need more support about this project, click on the “Ask Question” button on the top of this page to send me a message.

If you are new in doing science project, click on “How to Start” in the main page. There you will find helpful links that describe different types of science projects, scientific method, variables, hypothesis, graph, abstract and all other general basics that you need to know.  

Project advisor

Information Gathering:

Find out about soaps and their applications. Read books, magazines or ask professionals who might know in order to learn about the process of making soap.

Learn about sodium soaps, potassium soaps and soaps of other metals such as zinc and calcium.

Also learn about soaps that are made with different fats.

Keep track of where you got your information from.

Following are samples of information that you may find.

Fatty Acids

Some organic acids such as pulmitic, stearic and oleic acid are known as fatty acids. Fatty acids have a general formula of CnH2n+1COOH.

Some saturated fatty acids are:

Butyric: CH3(CH2)2COOH

Lauric(dodecanoic acid): CH3(CH2)10COOH

Myristic(tetradecanoic acid): CH3(CH2)12COOH

Palmitic(hexadecanoic acid): CH3(CH2)14COOH

Stearic(octadecanoic acid): CH3(CH2)16COOH

Arachidic(eicosanoic acid): CH3(CH2)18COOH

Fatty acids can be extracted from animal fats and vegetable fats. The process of extraction is known as hydrolysis, in which the molecules of fat will break down to the molecules of acids and molecules of alcohols. So fats are really a compounds of acids and alcohols. In organic chemistry compounds made by reaction of acid and alcohol are known as esters.

R-COOH + R’-OH ==> R-CO-R’

Acid + Alcohol ==> Ester

R and R’ have a general formula of CH3-(CH2)n –

Esters are usually encountered as sweet smelling organic compounds commonly produced by many plants and fruits. However, the most common esters found in nature are fats and  vegetable oils, which are esters of glycerol and fatty acids.

Most fats are composed primarily of  triglycerides.

Triglycerides (or triacylglycerols) are glycerides in which the glycerol is esterified with three fatty acids.. They are the main constituent of vegetable oil and  animal fats.

Animal fat is the triglyceride of stearic acid, CH 3 (CH 2 ) 16 COOH, i.e., the tristearate ester of glycerol; glycerol tristearate.

Please note: All soaps are esters; but, not all esters are soaps. Some esters are solvents, fragrances, flavors and monomers. Now you know why esters are so important. You may also know why some plastics are called polyester.

Making soap:

In the process of making soap triglycerides (fat) are reacted with sodium or potassium hydroxide to produce glycerol and a fatty acid salt, called ‘soap’.

Fat or lipids that contain fatty acid ester linkages can undergo hydrolysis. This reaction is catalyzed by a strong acid or base. Saponification is the alkaline hydrolysis of the fatty acid esters..

Percent Fatty Acid Present in Triglycerides
 Fat or Oil Saturated Unsaturated  
 Palmitic Stearic  Oleic Linoleic  Other
Animal Origin
 Butter 29 9 27 4 31
 Lard 30 18 41 6 5
 Beef 32 25 38 3 2
 Vegatable Origin
 Corn oil  10 4 34 48 4
 Soybean 7 3 25 56 9
 Peanut 7 5 60 21 7
 Olive 6 4 83 7


What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.

The purpose of this project is to experiment soap making and learn about the factors affecting the quality of the soap.

Identify Variables:

When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.

Independent variable (also known as manipulated variable) is the type of fat used in soap making.

Dependent variable (also known as responding variable) is the properties of the resulting soap.


Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis.

This is a sample hypothesis:

Stearic acid can be used to make soap with better or identical properties. My hypothesis is based on my study of the chemical reaction that makes soap.

If you want to test other fatty acids too, you may adapt a hypothesis like this:

Fatty acids such as stearic acid, lauric acid, pulmitic acid, oleic acid

Note that the results of your experiments may or may not support your hypothesis

Experiment Design:

Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”

Experiment 1: Making soap using stearic acid

Is this a good experiment for you?

Do this experiment only if you can find and purchase stearic acid. If you want to do additional experiments, you will also need to find and purchase other fatty acids such as palmitic acid and oleic acid.


In a normal process of soap making we add melted fat on sodium hydroxide solution. This reaction results a mixture of soap and glycerin. Then we have to add salt in order to separate soap from the mixture. The reason that we add salt is that soap does not dissolve in salt water, so adding salt will force the soap to separate from the solution. After we separate the soap, we have a leftover mixture of salt and glycerin. Utilizing or disposing this solution is an unpleasant burden on traditional soap makers. I am wondering if we can avoid such a byproduct by using fatty acid instead of fat.

Soap made of animal fat and caustic soda is Sodium stearate with the formula of CH3(CH2)16COONa. I am wondering if we can simply use sodium hydroxide and pure stearic acid (instead of fat) to make this soap. In this way we will not get glycerin as a byproduct and we don’t have to add salt to separate the soap.


Stearic Acid: CH3(CH2)16COOH (Molecular weight=284, Melting point=71ºC)

Caustic Soda (Sodium Hydroxide): NaOH (Molecular weight=40)

Steel Pots or glass beakers (Not aluminum)

Stirring rod or spoon

Safety note:

Sodium Hydroxide (Caustic Soda) is strongly corrosive; wear goggles, rubber gloves and protective clothing while handling caustic soda.


  1. In a 2 liter glass beaker or a steel pot dissolve 40 grams of Sodium Hydroxide in 500 ml of water. Warm up the solution if necessary to about 70ºC.
  2. In a separate container melt 284 grams of stearic acid. Stop the heat as soon as the entire acid is melted. (Note that fatty acids are not corrosive).
  3. Gradually add the entire melted stearic acid on the caustic soda solution while continuously stirring the solution.
  4. Continue to stir the compound for an additional 3 to 5 minutes while keeping it hot to complete the reaction.
  5. Transfer the newly made compound to a tray covered by a sheet pf plastic. Let it dry for a few days. Cut it to small squares and test them for their cleaning properties.


How consistent is the compound?

Do you still have to add salt in order to solidify and separate soap?

How does it smell like?

Use a wet pH paper to test the pH of the compound that you have made. How does it compare to the pH of the soaps that you have at home.

How wet is your product? Do you have to reduce or increase the amount of water? Why? (Note that very little water does not allow the reaction to complete; so, instead of soap you may get a mixture of caustic soda and stearic acid. Too much water will results a very wet product that takes a long time to dry.)

Additional Experiments:

You may repeat this experiment with 256 grams palmitic acid, or with 270 grams oleic acid. Note that 256 and 270 are the molecular weights of palmitic acid and oleic acid.

Experiment 2: Making soap with different animal and vegetable fats

Is this a good experiment for you?

This is a good experiment for everyone. In this experiment you try to find out how does your choice of fat affect the properties of the soap. Note that for this experiment your independent (manipulated) variable is the type of fat. The dependent (responding) variable is the ability of each soap to dissolve oils.


Fats can be extracted from varieties of plant and animal sources. Fats extracted from plants include corn oil, olive oil, peanut oil, soybean oil, linseed oil and many more. Fats extracted from animals include butter, lard, and beef fat. In some areas you may also purchase oils from sea animals such as wale. In this experiment you will try to find out “How do the properties of the soap vary when made with different types of fat?”


At least 3 different types of plant or animal fats

Caustic Soda (Sodium Hydroxide): NaOH (Molecular weight=40)

Steel Pots or glass beakers (Not aluminum)

Stirring rod or wooden spoon

Safety note:

Sodium Hydroxide (Caustic Soda) is strongly corrosive; wear goggles, rubber gloves and protective clothing while handling caustic soda.

Procedure (Part 1):

  1. In a 2 liter glass beaker or a steel pot dissolve 40 grams of Sodium Hydroxide in 500 ml of water. Warm up the solution if necessary to about 70ºC.
  2. In a separate container melt or warm up about 300 grams of the fat that you are testing. Make sure the fat is liquid and about 70ºC hot.
  3. Gradually add the entire melted or liquid oil stearic acid on the caustic soda solution while continuously stirring the solution.
  4. Continue to stir the compound for an additional 3 to 5 minutes while keeping it hot to complete the reaction.
  5. Add saturated salt solution or salt powder while stirring the hot solution until the soap curds float on the top.
  6. Let the mixture to cool off and then separate the solid soap curds from the top of the salt solution and dispose of the remaining solution. At this time the salt solution also includes glycerol and some unused caustic soda solution.
  7. Press the extracted soap in cheese cloth to remove extra water and leave the solid soap in a tray to dry.
  8. Repeat these procedures with at least 3 different fats.
  9. Compare the color, the odor, the hardness, the washing properties of the soaps that you have made.

Procedure (Part 2): This part is for students who need to have measurable results and a data table.

  1. Dissolve one gram of each soap in warm/ hot water in a small bottle
  2. Add 20 ml oil (corn oil is fine) to the bottle
  3. Swirl the mixture for 2 minutes so the soap water can dissolve the oil
  4. Let the mixture sit for one hour
  5. Separate and measure the amount of oil that remains un-dissolved

Your results table may look like this:

Type of soap Oil dissolved by 1 gram of soap

Materials and Equipment:


  1. Caustic Soda (Sodium Hydroxide)
  2. Stearic Acid
  3. Animal Fat
  4. Water
  5. Salt


  1. Beakers or steel pots
  2. Wooden spoon
  3. Scale
  4. Hotplate
  5. Thermometer

Results of Experiment (Observation):

Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.



Summary of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.


Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.


List of References


Saturated and unsaturated fats

Soap making

Hot Process Soap

I’ve been making soap for a few years now, and recently I’ve been experimenting with Hot Process Soapmaking. It’s a lot of fun, and it’s faster than cold process soap in that it (usually!) doesn’t require a cure time.

With Hot Process soap, you are doing two things in the pot – completely finishing the saponification process, *and* boiling off the excess water.

You may choose to use a little less water than your recipe dictates if you are doing Hot Process soap – however it is wise to be sure that you have sufficient to completely dissolve the lye prior to pouring into the oils.

IMPORTANT NOTE: This webpage assumes you are sufficiently experienced with cold process soapmaking and the safety issues associated with that addiction; in particular, do not attempt hot process soapmaking without adequate clothing, ventilation, eye/face/skin protection, readily available supplies of copious amounts of cold running water, and a good 2-3 hours uninterrupted by children, well-meaning spouses, or pets.

For newcomers to soap: Soapmaking is not rocket science. And it’s a lot of -extremely addictive- fun. But it can be very dangerous if you get the highly caustic lye *anywhere* on your skin. It burns. Sensible safety precautions are absolutely essential. Have I frightened you off yet?

I’m not going to go into the finer details of cold process soapmaking at this stage. Anyone who has a nice site with cp instructions, please let me know (apologies, I haven’t got enough time to search you out!) and I’ll include a link here.

Note also that I’m using an all-veggie recipe (It’s what I call the ‘Ozzie Supermarket Shelf’ Recipe, as you can get everything you need at Coles or Action!!) Anyone interested in the recipe, let me know, eh!

If you’re wanting to put together your own recipe, there are a number of sites around that will let you do that; I personally use Therese Lott’s Excel Sap Calculator, which is just *brilliant* and very easy to use. Once again, let me know if you want a link to a lye calculator on your site here.

Please also excuse the state of these pages – I’m primarily out to (finally!) get the pictures up and running – so, I’m after information rather than graphic brilliance right now. But please do let me know if you can’t read the instructions, or if you have any other problems (including problems in *following* the instructions!!!)











Here’s my son Daniel. (Well did you think I could take a picture of myself all dressed up in soapmaking gear?). If you’re not dressed like this, or a reasonable approximation thereof, you’re not ready to make soap. (And no, they don’t make Bananas in Pyjamas plastic coats in adult size. Yet.)

Did you spot the deliberate mistake? Daniel’s not wearing long trousers. Our excuse: it was the middle of an Ozzie summer and over 40degreesC outside – he didn’t want to wear long pants when he wasn’t going to get a go of making soap…. But don’t *you* try this at home folks – bare skin is a no-no where lye is concerned!











Here’s the oils, ready to go. Make sure the liquid oils are in the pot before you start heating – it’s safer and you don’t get burned patches appearing on the bottom of the pan that later transfer themselves to your soap.










This is the way we pour the lye into the water (note: **LYE into WATER** please – otherwise you could get an explosion – this mixture heats up incredibly!!)

Yes, I can see I have a dirty pot here. At the time I took the photograph, I couldn’t. Another safety requirement for soapmaking – GOOD LIGHTING. There could have been *anything* in that pot, eh.











Pouring lye water into the melted oils. This picture shows the pour far slower than I really do it. I slowed the pour so that I could take the picture with the other hand before I ran out of lyewater! With cold process the temperatures of the oils and lyewater might matter, as might the rate of pour. With hot process, you pour lye as soon as the oils are melted, regardless of what temperatures you have for each component.











This is Trace. Gidday Trace. In hot process soapmaking, trace is sometimes present for a fraction of time – maybe 10 seconds or so – and sometimes you don’t get to see it at all, as the mix wooshes through trace to separation.











This is separation. See the curds of soap, resting on the bottom of the pot, covered by the oil, and floating on the very surface is that scummy stuff – well, that’s the bit we want, folks – that’s finished soap. In order to translate the curds and oil into finished soap, you need to heat the pot. GENTLY. And keep stirring ALL the time.

The first time I did this, the heat was too high, and I didn’t know enough to stir all the time. Result: Volcanoes of caustic mix jumping higher than my head, and etching of the base of the pot by the caustic solution. NOT something you want to have happen to you. So stir. ALL the time the pot is on the heat, eh.











Ok the mix is now boiling merrily along. DON’T STOP HEATING. Keep the gentle heat and the stirring going. You need to keep going for approximately 20 minutes from boiling point, to start with.









Those huge boiling bubbles that appeared when the mix first hit boiling point, have gradually reduced in size until the whole top of the pan is filled with frothy ‘champagne’ bubbles. The darker yellow swirls you can see are finished soap, and when the whole batch is finished, that’s what it will look like in the pot. Consistency of old petroleum jelly… but I’m getting ahead of myself. Next photo….










Here’s a close up of the champagne bubbles. Right in the centre of the pot you can see there are still some larger bubbles happening; soon as these settle down to one or two spots only, then you can stop (relief!!) for a while.










Here we go. The pot is full of champagne bubbles, with some finished soap on top and the heat is turned OFF. You can leave the pot for about 10 minutes – but don’t go too far away – you’ll see why later on!











Looks like a cake baking, doesn’t it! The exothermic (giving off heat) reaction of saponification is continuing the process all by itself, even though there’s no heat being applied to the pot. What you can see in the middle is the champagne bubbles reaching the top surface of the mix, and the darker, cooling areas of finished soap separate in the middle and slide down the sides of the pot. The whole thing will keep turning quite nicely like this all by itself for a few minutes.










Here’s a close up of that process. The heat is off, and the pot is turning the soap by itself. This is the stage that it starts to smell good.










The heat’s been off for about 10 minutes now, the champagne bubbles are no longer breaking through the surface as the soap is turning in the pot.











By breaking the surface of the soap, you can see that the champagne bubbles are continuing to work. You’ve got three layers here; the champagne bubbles, and on top of that the darker finished soap, and on top of that the whiter cooled finished soap. That top colour is the colour your finished, cooled and cut soap will be. (Exciting, isn’t it!!)









When the pot looks like this, it’s time to reheat. Just as a matter of interest, I have left a pot for a couple of hours to go completely cold when I had to race out one time – I simply reheated it up through boiling to the champagne bubble stage again and all was fine….. It’s my fond belief (never wrong yet!!) that no soap is ruined unless you’ve burned it in the pot (and that is utterly disgusting and I wouldn’t wish burned soap on my worst enemy!!)









Here’s a close up of the soap ready to reheat. Once again, a gentle heat, and stir all the time the heat is on. Make sure you stir into all the corners and across all the base of the pot, to avoid volcanoes.









Champagne bubbles starting to form, second time around.










It’s a good idea to turn off the heat now, and once again, don’t walk too far away, because……










If you carry on heating the soap, sometimes it doesn’t know when to stop rising after you turn the heat off…….











And it can try climbing out of the pot. If this happens, stir it down, incorporating air as you stir – the air will cool the mix little by little, until you get the soap ‘turning’ as it did previously.

Once again, wait until the champagne bubbles no longer break the surface of the soap before re-heating again. Repeat this ‘heat and stir-champagne bubble-turn off heat’ cycle until, all of a sudden, something else happens.










Suddenly, as you heat and stir, instead of champagne bubbles, the mix will all at once ‘meld together’ as is shown in the picture above. It’s like a gel, almost…..










Here’s a close up. At this stage the soap is nearly done (YAAAAY!!) and you just need to heat a little more to drive off some more of the water, and complete the saponification process.










This is ready to pour – er, glop – into the mold. It hasn’t been coloured or fragranced (more on that below). If you want to superfat, now is the time to do it – a few ml of Jojoba can add a marvellous ‘silkiness’ to the gloppy gel in your pot!










If you heat much beyond this point, you can get a situation where the soap dries out too much and does not want to stick to itself in the mold, but crumbles instead. If this happens to you, try a little extra oil (for example I’ve sometimes added 50ml of Almond oil in a 1.7Kg oil batch if the final product seemed too dry)










This is the way we glop the soap, glop the soap, glop the soap…… it’s almost like a rebatch, but it’s a delightful light colour, with no lumps of unmelted soap in it – the lighter bits are just cooler than the darker bits, and that disappears after the soap is cooled and cut.













And there you go – the cleanest soap pot you’re likely to see in a while! Note that the surface of the soap isn’t very pretty – this can be shaved off when cutting, and made into soapballs etc. I’ve pictured a particularly ‘dry’ batch here to show you how the soap doesn’t want to stick to itself if it gets too cold, which is what happened to the surface whilst I was fiddling with the camera. By the time I smooshed it all down into the mold, it was a bit late for a few lumps of soap.

Now, if you’ve completed saponification, the soap will be ready to use soon as it’s cooled and cut (try the tongue test – but be careful! If your tongue starts tingling 1/2 cm away from the soap – give it a week to cure and try again!) If you haven’t boiled off a sufficient amount of water, the soap will be ‘wet’ to cut, and will shrink somewhat when drying (If it’s wet, don’t pack in shrinkwrap straight away – not a pretty sight four weeks later!!)

The jury’s still out on fragrancing, but at this stage (thanks to some buddies from the Soap List!) I’ve experimented with fragrancing at around 100degreesC – any cooler and the soap wants to fracture rather than hold together, the fragrance doesn’t mix in properly, and the soap needs to be packed into the mold under pressure in order to avoid crumbling.

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