Stearic acid

Key takeaways

Stearic acid belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Stearic acid to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Stearic acid from memory before moving on to harder problems.

Reference excerpt

Stearic acid ( STEER-ik, stee-ARR-ik) is a saturated fatty acid with an 18-carbon chain. The IUPAC name is octadecanoic acid. It is a soft waxy solid with the formula CH3(CH2)16COOH. The triglyceride derived from three molecules of stearic acid is called stearin. Stearic acid is a prevalent fatty acid in nature, found in many animal and vegetable fats, but is usually higher in animal fat than vegetable fat. It has a melting point of 69.4 °C (156.9 °F) and a pKa of 4.50. Its name comes from the Greek word στέαρ "stéar", which means tallow. The salts and esters of stearic acid are called stearates. As its glycerol ester, stearic acid is one of the most common saturated fatty acids found in nature and in the food supply, following palmitic acid. Dietary sources of stearic acid include meat, poultry, fish, eggs, dairy products, and foods prepared with fats; beef tallow, lard, butterfat, cocoa butter, and shea butter are rich fat sources of stearic acid.

Production In terms of its biosynthesis, stearic acid is produced from palmitoyl-CoA, with malonyl-CoA a two-carbon building block (after decarboxylation). Stearic acid is obtained from fats and oils by the saponification of the triglycerides using hot water (about 100 °C). The resulting mixture is then distilled. Commercial stearic acid is often a mixture of stearic and palmitic acids, although purified stearic acid is available. Commercially, oleic acid, as found in palm and soy, can be hydrogenated to give stearic acid.

Uses and occurrence In general, the applications of stearic acid exploit its bifunctional character, with a polar head group that can be attached to metal cations and a nonpolar chain that confers solubility in organic solvents. The combination leads to uses as a surfactant and softening agent. Stearic acid undergoes the typical reactions of saturated carboxylic acids, a notable one being reduction to stearyl alcohol, and esterification with a range of alcohols. This is used in a large range of manufactures, from simple to complex electronic devices.

Food Of the saturated fatty acids consumed in the United States, stearic acid consumption is second (26% of total saturated fatty acid intake) to palmitic acid (56% of total saturated fatty acid intake). Stearic acid is more abundant in animal fat (up to 33% in beef liver) than in vegetable fat (typically less than 5%). The important exceptions are the foods cocoa butter (34%) and shea butter, where the stearic acid content (as a triglyceride) is 28–45%. Examples of the use of stearic acid in food manufacturing include baked goods, frozen dairy products, gelatins, puddings, hard candy, and nonalcoholic beverages. Stearic acid (E number E570) is found in some foods.

Soaps and cosmetics Stearic acid is mainly used in the production of detergents, soaps, and cosmetics such as shampoos and shaving cream products. Stearate soap, such as sodium stearate, could be made from stearic acid but instead are usually produced by saponification of stearic acid-containing triglycerides. Esters of stearic acid with ethylene glycol (glycol stearate and glycol distearate) are used to produce a pearly effect in shampoos, soaps, and other cosmetic products.

Lubricants, softening and release agents In view of the soft texture of the sodium salt, which is the main component of soap, other salts are also useful for their lubricating properties. Lithium stearate is an important component of grease. The stearate salts of zinc, calcium, cadmium, and lead are used as heat stabilizers for PVC. Stearic acid is used along with castor oil for preparing softeners in textile sizing. They are heated and mixed with caustic potash or caustic soda. Related salts are also commonly used as release agents, e.g. in the production of automobile tires. As an example, it can be used to make castings from a plaster piece mold or waste mold, and to make a mold from a shellacked clay original. In this use, powdered stearic acid is mixed in water and the suspension is brushed onto the surface to be parted after casting. This reacts with the calcium in the plaster to form a thin layer of calcium stearate, which functions as a release agent. Stearic acid can be converted to zinc stearate, which is used as a lubricant for playing cards (fanning powder) to ensure a smooth motion when fanning. Stearic acid is a common lubricant during injection molding and pressing of ceramic powders.

Niche uses Being inexpensive, nontoxic, and fairly inert, stearic acid finds many niche applications. Varied examples of stearic acid use in manufacturing include soaps and greases, household soap products, synthetic rubber, cosmetic and pharmaceutical creams and lotions, candles, phonograph records, lubricants, shoe and metal polishes, food packaging, and rubber compounds. Stearic acid is used as a negative plate additive in the manufacture of lead-acid batteries. It is added at the rate of 0.6 g per kg of the oxide while preparing the paste. It is believed to enhance the hydrophobicity of the negative plate, particularly during dry-charging process. It also reduces the extension of oxidation of the freshly formed lead (negative active material) when the plates are kept for drying in the open atmosphere after the process of tank formation. As a consequence, the charging time of a dry uncharged battery during initial filling and charging (IFC) is comparatively lower, as compared to a battery assembled with plates which do not contain stearic acid additive. Fatty acids are classic components of candle-making. Stearic acid is used along with simple sugar or corn syrup as a hardener in candies.

Metabolism An isotope labeling study in humans concluded that the fraction of dietary stearic acid that oxidatively desaturates to oleic acid is 2.4 times higher than the fraction of palmitic acid analogously converted to palmitoleic acid. Also, stearic acid is less likely to be incorporated into cholesterol esters. In epidemiologic and clinical studies, stearic acid was found to be associated with lowered LDL cholesterol in comparison with other saturated fatty acids.

Examples Salts Potassium stearate Calcium stearate Cobaltous stearate Lithium stearate Magnesium stearate Mercuric stearate Sodium stearate Zinc stearate Esters Estradiol stearate Glycol stearate Stearin Testosterone stearate

References

External links

NIST Chemistry WebBook Entry

Illustrations

Worked examples

Example 1 — a first encounter with Stearic acid

Start with the simplest possible case. Write down what Stearic acid claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Stearic acid before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Stearic acid ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Stearic acid

In research: Stearic acid appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Stearic acid in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Stearic acid is common in secondary-school and first-year university syllabi. It links to neighbouring topics Alkanoic acids, E-number additives, Fatty acids, so understanding it makes those chapters shorter.
In everyday life: Look for Stearic acid outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Stearic acid in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Stearic acid means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Stearic acid out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Stearic acid in simple terms?

Stearic acid ( STEER-ik, stee-ARR-ik) is a saturated fatty acid with an 18-carbon chain. The IUPAC name is octadecanoic acid.

Why does Stearic acid matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Stearic acid?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Stearic acid.