Link to the lesson

Higher carboxylic acids

Carboxylic acids, among others the acetic acid $\text{C}{\text{H}}_{\text{3}}\text{COOH}$ or butyric acid ${\text{C}}_{\text{3}}{\text{H}}_{\text{7}}\text{COOH}$, due to the small number of carbon atoms in the hydrocarbon chain, are classified as lower carboxylic acids. Higher carboxylic acidshigher carboxylic acidsHigher carboxylic acids are compounds containing a long carbon chain (a dozen or so carbon atoms) as well as the group $\text{– COOH}$ which is characteristic of carboxylic acids.

Higher carboxylic acids are also called fatty acids. Fat molecules contain radicals of fatty acids.

Division of higher carboxylic acids

Remember the concept of organic saturated and unsaturated compounds. Do you recall which hydrocarbons are classified as saturated, and which as unsaturated?

There are saturated and unsaturated fatty acids.

Saturated higher carboxylic acids include palmitic acidpalmitic acidpalmitic acid that has the following formula: ${{\text{C}}_{\text{15}}\text{H}}_{\text{31}}\text{COOH}$, as well as stearic acidstearic acidstearic acid ${\text{C}}_{\text{17}}{\text{H}}_{\text{35}}\text{COOH}$. In the molecules of these acids, there are single bonds between carbon atoms. Oleic acidoleic acidOleic acid ${\text{C}}_{\text{17}}{\text{H}}_{\text{33}}\text{COOH}$ contains a double bond between the 9th and 10th carbon atoms, which is why it belongs to unsaturated organic compounds.

Properties of higher carboxylic acids

Stearic and palmitic acids melt at low temperatures. Carboxylic acids undergo the combustion reaction. They burn with a yellow flame – like the one we observe while candles burn.

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Exercise 1

Wybierz dowolne angielskie słówko ze słowniczka i zapytaj kolegę o jego znaczenie.

Wybierz dowolne angielskie słówko ze słowniczka i zapytaj kolegę o jego znaczenie.

Arrange the signatures on the diagram to correctly represent the distribution of higher carboxylic acids.

stearic acid, saturated, oleic acid, unsaturated

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Exercise summary
In order to distinguish stearic or palmitic acid from oleic acid, use bromine water ${\text{Br}}_{\text{2(aq)}}$ or a solution of potassium permanganate ${\text{KMnO}}_{\text{4}}$. The molecules of unsaturated oleic acid contain a double bond and therefore discolor the bromine water and the solution of potassium permanganate. What is more, this reaction produces a white solid – saturated stearic acid. It transitions into a saturated acid, which we observe as a change in the state of the substance from liquid to solid. Higher carboxylic acids introduced into water with the addition of methyl orange do not change the color of the indicator because they do not dissolve in water and do not undergo the process of electrolytic dissociation.

How are soaps made?

Fatty acids play an important role in obtaining soaps.

Reaction of stearic acid with a sodium hydroxide in the presence of phenolphthalein

Experiment 2

Research problem

Will the reaction of higher carboxylic acid with sodium hydroxide produce salt?

Hypothesis

Stearic acid reacts with the sodium hydroxide, and the products of this reaction are salt and water.

You will need

• stearic acid,

• aqueous solution of sodium hydroxide,

• phenolphthalein,

• burner,

• test tubes.

Instruction

1. Pour a small amount of stearic acid into a test tube.

2. Pour in a few cubic centimeters of the aqueous solution of sodium hydroxide.

3. Add a few drops of phenolphthalein.

4. Heat the mixture.

5. Observe the changes.

6. Leave the substance to cool down.

Summary

The mixture of stearic acid and sodium hydroxide melts. The raspberry color disappears. We observe foaming of the reaction product. After cooling down, a lumpy substance with a soap‑like consistency is created.

Stearic acid reacts with the sodium hydroxide to form soap. The reaction proceeds according to the following equation:

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Równanie reakcji: kwas stearynowy - stearic acid - reaguje z wodorotlenkiem sodu - sodium hydroxide -powstaje stearynian sodu - sodium stearate - i woda - water, czyli c siedemnaście ha trzydzieści pięć c o o ha dodać en a o ha strzałka w prawo c siedemnaście ha trzydzieści pięć c o o en a dodać ha dwa o.

Sodium stearate is the water‑soluble sodium salt of stearic acid.

The salts of higher carboxylic acids, e.g. palmitic, stearic and oleic, are soaps.

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Ilustracja przedstawia typy mydeł. Pierwszy typ: "sodium soap". Charakterystyka "sodium soap" - "hard and white, soluble in water, after adding fragrances to them, dyes, toiler soaps are obtained". Drugi typ: "potassium soap". Charakterystyka "potassium soap" - "soft, called gray soap, soluble water id used, among others for washing". Trzeci typ: "magnesium soap". Charakterystyka "magnesium soap" - "liquid, sparingly soluble in water, in used in the production of shampoos, bath lotions and liquid soaps".

Conclusion

• Higher carboxylic acids are acids containing long carbon chains.

• Higher carboxylic acids are also referred to as fatty acids because fat molecules contain the radicals of these acids.

• Saturated fatty acids include palmitic and stearic acids.

• Oleic acid is an unsaturated fatty acid.

• Soaps are the salts of higher carboxylic acids.

Keywords

carboxylic acid, long‑chain monocarboxylic acids, molecular formula, fatty acid, palmitic acid, stearic acid, oleic acid

Glossary