soaps and detergents

Question 1

What kind of molecule is a soap? What about a detergent? What do both. soap and detergents act as?

Answer 1

Both are surfactants. A surfactant is a type of molecule. They both act as an emulsifying agent.

Question 2

What is an emulsifying agent?

Answer 2

An emulsifying agent is a substance which allows immicible liquids to mix.

An immiscible liquid is one that cannot be mixed naturally, such as oil and water.

Question 3

what is a soap?

Answer 3

A soap is a conjugate base of fatty acids. Soaps are generally sodium salts of a fatty acid.

A fatty acid is a carboxylic acid with a long hydrocarbon chain and a carboxyl group. (functional group of carboxylic acid)

Question 4

What is a saturated compound in organic chemistry? What does it imply with the bonds?

Answer 4

A saturated compound has single bonds only.

An unsaturated compound will have a double bond.

Question 5

What is the structure of a soap? Explain with reference to polarities

Answer 5

A soap consists of a non-polar hydrophobic tail and a polar hydrophillic carboxylate head.

Together, the soap is an amphiphillic compound, which means that is has a polar component as well as an unpolar component.

Question 6

How are soaps produced?

Answer 6

Soaps are produced by heating fats or oils with a concentrated alkaline solution

Remember that an alkaline solution is a basic solution, with low acidity.

This reaction is called saponification. wherein the ester of the fat molecules undergoes basic hydrolysis to produce a carboxylate sodium salt, also known as the soap.

(basic here means high pH, low acidity)

Question 7

What happens when an ester undergoes acidic hydrolysis?

What about when an ester undergoes basic hydrolysis?

What type of hdyrolysis is saponification?

Answer 7

An ester with acid hydrolysis will produce a carboxylic acid

An ester with basic hydrolysis will produce carboxylate

A carboxylate is ONLY the -COOH part whereas the carboxylic acid is the compound containing this carboxylate functional group.

Saponifcation which is the production of soap, is a basic hydrolysis reaction

Question 8

All fat and oils are naturally occurring esters. True or false.

Answer 8

True. Fats and oils contain triglycerides, which is a type of ester.

Question 9

What is hydrolysis?

Answer 9

A hydrolysis reaction is when a compound reacts with water which breaks its chemical bonds.

Dissolving is NOT A HYDROLYSIS REACTION. Dissolving a solute is a physcial change, not a chemical change. Therefore, hdyrolysis is when water is used to break down the chemical bonds of the substance, due to its polarity and ability for hydrogen bonding.

Esters react with water to from a carboxylic acid and an alcohol.

Acid hydrolysis is when the compound reacts with the H+ ions of water

Basic hydrolysis is when it reacts with OH ions

Question 10

Is dissolving something a physical change or a chemical change?

Answer 10

Dissolving something/ ksp is a physcial change.

Dissolving refers to the process in which a solute (such as a salt, sugar, or other substance) dissolves into a solvent to form a solution. During this process, the solute particles break apart and mix uniformly with the solvent, but no chemical reaction necessarily occurs. For example, when salt (NaCl) dissolves in water, it dissociates into Na⁺ and Cl⁻ ions, but this process does not involve a chemical reaction between the salt and water.

Dissolving something is also reversible therefore a physical reaction

Question 11

Write the equation for the production of soap. Remember that triglyceride is the chemical term for ‘fat’

Answer 11

Triglyceride + 3NaOH –> Gycerol + Soap

Remember, triglyceride is an ester and an ester forms an alcohol and a carboxylic acid with water.

However, reacting triglyceride with sodium hydroxide is a basic hydrolysis reaction, as there are hydroxide ions which make it alkaline. Therefore, this reaction is saponifcation, which produces soap, also known as a carboxylate salt.

Question 12

What is emulsion? What causes emulsion?

Answer 12

Emulsion is when the non-polar fat is distributed across the solvent. (When there are multiple micelles, as the fat components are separated and surrounded by soap.

The amphiphillic nature (polar+non-polar)
of soap allows for fat and water to form emulsions.

Question 14

Agitation is crucial for the soap/ detergent to break off the fat. True or false?

Answer 14

True, agitation is necessary.

Think of agitation as friction, you need force to mix the soap with the fat.

For example, washing your hands by rubbing them together or spinnning the laundry with detergent

Question 15

What charge is the amphillic head of the soap?

Answer 15

Negatively charged

Question 15

What kind of intermolecular forces do the hydrophillic heads produce with the water molecules?

What about the hydrophobic tails with the fat molecule?

Answer 15

The hydrophillic head is negatively charged and is thus polar. It produes an ion dipole with the water.

The tails produce dispersion forces with the fat molecule, since both are non-polar. Remember, the tails only surround the fat, not inject itself in it.

Question 15

What is a micelle? How is it formed?

Answer 15

A micelle is when the oil is surrounded by soap molecules, such that the hydrophobic tails surround the oil in a spherical shape, with the hydrophillic heads facing outwards, interacting with the water.

(The tails surround the oil/fat, but doesn’t penetrate/inject inside of it)

Question 16

What is the limitation of soap? What is meant by ‘hard water?’

Answer 16

When used in hard water, soap forms a precipitate called soap scum, which is unwanted.

‘hard water’ is water that contains high concentrations of calcium and magnesium ions. Thus, the cations in hard water react with the carboxylate ions RCOO- bit, to form a precipitate.

In addition, soap is not effective in acidic/ low pH water

Question 17

What are detergents? What sets them apart from soap?

Answer 17

Detergents are synthetic surfactants, meaning they are soap but made artificially by humans.

Detergents are made from crude oil and their unique structures make it more effective than soap.

To distinguish between a soap and a detergent, just remember that soaps have a carboxylate head and detergents do not.

Question 18

What is an ion-dipole and when is it formed?

Answer 18

An ion-dipole is a type of intermolecular force. It is formed when an ionic compound or ion interacts with a polar solvent such as water.

Therefore, a sodium ion in water will form an ion dipole. The ion can be either cation or anion

Question 19

What happens when oil is added to water containing micelles?

Answer 19

The micelles grow larger in size as they absorb the oil towards its core, due to the hydrophobic nature of the oil. Therefore, the oil technically coexists with the water, instead of forming a distinct immiscible layer. However, if too much oil is poured, then some will still remain floating on top of the water, as oil is less dense than water

Question 20

What is emulsion?

Answer 20

When one liquid is dispersed as tiny droplets within another liquid. (In this context, oil/fat exists in water as micelles, scattered throughout it)