M7 Soaps

Question 1

How is soap made

Answer 1

through the hydrolysis of a fat under basic or acidic conditions(Strong acid or base) (saponification)

Question 2

what is the chemical reaction of saponification

Answer 2

Heat

Fat + NaOH —> Glycerol + 3 sodium fatty acid carboxylate(soap)

Question 3

How can you identify a fat

Answer 3

the triglyceride (carbon chain) connecting three carbon chains

Question 4

what are the major components of a soap molecule (2)

Answer 4

• Polar/Ionic Hydrophilic head (COO-)

- a non-polar Hydrophobic tail (carbon chain)

Question 5

why can’t fats and oils interact with water

Answer 5

they are non-polar and only emit dispersion forces meaning they do not have the strength to overcome the intermolecular h-bonds between water molecules therefore making it unable to interact with water

Question 6

what happens when you put soap in water

Answer 6

when dissolved in water, soap molecules act as surfactants arranging themselves in the form of roughly spherical aggregates called a micelles, which have a polar outside with a hydrophobic pocket on the inside

Question 7

How do Micelles help with cleaning oils and fats (2)

Answer 7

• Micelles hydrophobic pocket, are able interact and solubilize other hydrophobic molecules, such as oils and fats as they are both non-polar
• As the hydrophilic head is attracted to polar water molecules by ion-dipole interactions, the oil is then able to disperse emulsifying within the water when agitated.

Question 8

what are instances where soap does not work (2)

Answer 8

• in an acidic solution

- in hard water

Question 9

why do soaps not work in acidic solutions

Answer 9

because the hydrogen ions react with soap creating a insoluble fatty acid

Question 10

what is an example reaction of soap in an acidic solution

Answer 10

CH₃(CH₂)₁₆COO⁻Na⁺ + HCl → CH₃(CH₂)₁₆COOH₍ₛ₎ + Na⁺ + Cl⁺

Question 11

what is hard water

Answer 11

water containing heavy metal ions such as Ca²⁺ and Mg²⁺

Question 12

why does soap not work in hard water

Answer 12

as the soap molecules forms strong intermolecular bonds between it and the heavy metal forming a scum

Question 13

what is an example reaction of soap in hard water

Answer 13

2CH₃(CH₂)₁₆COO⁻Na⁺ + Ca²⁺ → [CH₃(CH₂)₁₆COO⁻]₂Ca²⁺₍ₛ₎+ 2Na⁺

Question 14

What are the types of detergents and what type head group do they have

Answer 14

• anionic detergents: negatively charged head group
• ionic detergents: Positively charged head group
• non ionic detergents: non-ionic head group

Question 15

What makes detergents better to use than soaps (2)

Answer 15

• in hard water calcium and magnesium ions bond to the polar head of soap molecules preventing them from acting as a surfactant and producing a scum
• where as detergents do not bond to the magnesium and calcium and therefore can still act as a surfactant whilst in hard water

Question 16

What are some environmental impacts detergents have on the environment (3)

Answer 16

• Biodegradability
• Phosphates (eutrophication)
• Biocidal properties

Question 17

What is issue with biodegradability in detergents and how was it prevented (2)

Answer 17

• Problem: Early detergents due to there highly branched hydrocarbon tails, used to persist in the environment causing many waterways to foam up
• Solution: Solved issue by using a catalyst to create non branching tails that broke down in a couple of days

Question 18

What is issue with Phosphates (eutrophication) in detergents and how was it prevented (2)

Answer 18

• Problem: phosphates where added to give greater cleansing ability to the detergents, but if not managed would find their ways into waterways increasing nutrients in bodies of water leading to algal blooms and the eutrophication.
• Solution: detergents marketed as green, replaced phosphates with sodium zeolite which cannot be used as nutrients.

Question 19

What is issue with Biocidal properties in detergents and how was it prevented (2)

Answer 19

• Problem: cationic detergents, are attracted to bacterial cells, which are used in wastewater and sewage treatment and can disrupt its cellular processes
• Solution: cationic detergents only representa small amount of detergents used