Preparing Soap: Experiment 9

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Questions and Answers

What happens to soap when it is used in hard water?

It converts to free fatty acid

It forms insoluble calcium salts of the fatty acids and other precipitates (correct)

It reacts with the water to form a gas

It becomes more effective as a cleanser

What is the purpose of adding water softeners to soap?

To convert the soap to free fatty acid

To make the soap more acidic

To remove the hard-water ions and prevent the formation of precipitates (correct)

To make the soap more effective in soft water

What is the result of adding sodium carbonate to hard water when using soap?

The soap becomes more effective as a cleanser

The soap is converted to free fatty acid

The hard-water ions are precipitated as calcium carbonate (correct)

The water becomes more acidic

What is the process called when making soap from fats and oils?

Saponification Signup and view all the answers

What is the product of the reaction between soap and hydrochloric acid?

Free fatty acid and sodium chloride Signup and view all the answers

What is the reverse process of esterification?

Hydrolysis Signup and view all the answers

What is the primary function of micelles in terms of oil-soluble substances?

To absorb oil from an aqueous phase into their interior Signup and view all the answers

What is the range of carbon atoms in soap molecules that allows them to effectively solubilize oils and greases?

10 to 20 carbons Signup and view all the answers

Why have synthetic detergents largely replaced soap in recent decades?

Soap has two serious drawbacks Signup and view all the answers

What type of interactions occur between soap micelles and oil molecules?

Van der Waals interactions Signup and view all the answers

What happens to soap molecules with less than 10 carbons in terms of solubilizing fats?

They are ineffective in solubilizing fats Signup and view all the answers

What is the role of soap micelles in washing skin and clothing?

To solubilize oils and greases, allowing them to be washed away Signup and view all the answers

What is the significance of the structure of soap micelles in solubilizing oils and greases?

The head of the micelle is hydrophilic and the tail is hydrophobic Signup and view all the answers

What is the result of soap micelles coming into contact with oil molecules in an aqueous phase?

The oil molecules are absorbed into the interior of the micelles Signup and view all the answers

What is the primary function of the polar end of a soap molecule?

To solubilize the fatty acid in water Signup and view all the answers

What is the characteristic of a soap molecule that allows it to lower the surface tension of water?

Its arrangement at the water surface with polar ends immersed in water Signup and view all the answers

What is the term for the submicroscopic grouping of soap molecules that forms a tiny liquid droplet with charged groups on the outside and hydrocarbon chains on the inside?

Micelle Signup and view all the answers

What is the purpose of adding saturated NaCl solution to the soap mixture?

To precipitate or salt out the soap Signup and view all the answers

What is the typical number of carbon atoms in a fatty acid?

10 to 20 Signup and view all the answers

What is the purpose of washing the precipitate soap with 15 mL of ice-cold water?

To remove excess NaCl from the soap Signup and view all the answers

What type of soap usually consists of potassium salts of fatty acids?

Liquid soap Signup and view all the answers

What is the term for the property of a soap molecule that makes it soluble in water?

Hydrophilicity Signup and view all the answers

What is observed when a small piece of soap is added to a mixture of water and vegetable oil?

A temporary emulsion of tiny oil droplets in water is formed Signup and view all the answers

What is the purpose of warming the beaker with the soap solution?

To dissolve the soap completely Signup and view all the answers

What occurs when the concentration of soap is increased to a certain point?

The mixture becomes turbid due to the formation of colloidal spherical micelles Signup and view all the answers

What is the purpose of adding 2 drops of 5% calcium chloride solution to tube #1?

To test the reaction of the soap with hard water Signup and view all the answers

What is the purpose of the nonpolar hydrocarbon chain in a soap molecule?

To protrude from the water surface and increase the surface tension Signup and view all the answers

What is the purpose of using wide-range pH paper in tube #5?

To test the alkalinity or basicity of the soap solution Signup and view all the answers

What is the difference between the emulsions formed in the two test tubes?

One is more stable than the other Signup and view all the answers

What is the main purpose of the experiment?

To study the reactions of soap with hard water Signup and view all the answers

What is the primary purpose of adding 25% NaOH solution to the vegetable oil in the soap preparation process?

To facilitate the reaction between the oil and the sodium hydroxide Signup and view all the answers

What is the role of the 95% ethanol in the soap preparation process?

To act as a solvent Signup and view all the answers

What is the purpose of placing the flask with its contents in an ice-water bath after heating?

To cool down the mixture and stop the reaction Signup and view all the answers

What is the name of the compound formed when the vegetable oil reacts with the sodium hydroxide?

Sodium stearate Signup and view all the answers

What is the role of the boiling chips in the experimental procedure?

To prevent the mixture from boiling too vigorously Signup and view all the answers

What is the purpose of using a Büchner funnel in the experimental procedure?

To filter the mixture and separate the soap and glycerol Signup and view all the answers

What is the purpose of using PH paper in the experimental procedure?

To monitor the pH of the reaction mixture Signup and view all the answers

What is the purpose of using a hot plate in the experimental procedure?

To heat the mixture gently Signup and view all the answers

Study Notes

Introduction to Soap

A soap is the sodium or potassium salt of a long-chain fatty acid.
Fatty acid usually contains 10 to 20 carbon atoms.
Solid soaps usually consist of sodium salts of fatty acids, whereas liquid soaps consist of the potassium salts of fatty acids.

Structure and Properties of Soap

Soap consists of a molecule containing a polar group (ionized) that is water-soluble and a nonpolar hydrocarbon portion that is water-insoluble.
Soap molecules arrange themselves at the water surface with their polar ends immersed in the water and hydrocarbon chains protruding from the surface, lowering the surface tension of water and producing bubbles.

Micelles

Micelles are submicroscopic groupings of soap molecules forming a tiny liquid droplet with charged groups on the outside and hydrocarbon chains on the inside.
Micelles act as solvents for oil-soluble substances, absorbing oil molecules from an aqueous phase into the interior by van der Waals interactions.
Micelles must be composed of soaps containing 10 to 20 carbon atoms to be effective in solubilizing oils and greases.

Drawbacks of Soap

Soap becomes ineffective in hard water, which contains appreciable amounts of Ca²⁺ or Mg²⁺, forming insoluble calcium salts of fatty acids and other precipitates (curds).
In an acidic solution, soap is converted to free fatty acid and loses its cleansing action.

Water Softeners

Water softeners, such as sodium carbonate or sodium phosphate or borax (Na₂B₄O₇), are added to soaps to remove hard-water ions, allowing soap to remain effective in hard water.

Soap Making (Saponification)

Soap is made from a variety of fats and oils by a process called saponification (hydrolysis), involving boiling the oil or fat in a basic solution such as lye (NaOH) or potash (KOH).
The products of this reaction are glycerol and the soap (the salt of a long-chain fatty acid).

Optional Ingredients in Bar Soaps

Optional ingredients that are added to bar soaps include zinc oxide to make the soap whiter, lanolin to act as an emollient, pumice to help remove heavy soil by abrasion, and perfumes.

Experimental Procedure

The experimental procedure involves preparing soap from vegetable oil, ethanol, and sodium hydroxide, and then testing its emulsifying properties and reactions in hard water.

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Description

This experiment aims to prepare soap from olive oil and explore its properties, including the difference between sodium and potassium salts of fatty acids.