SmarterEd

Aussie Maths & Science Teachers: Save your time with SmarterEd

CHEMISTRY, M7 2025 HSC 9 MC

Some Torres Strait Islander Peoples pound the leaves of the vine Derris uliginosa to extract a chemical called saponin. Saponin is a relatively large molecule that contains both a water-soluble carbohydrate chain and a fat-soluble side chain.

Which is the most likely use of saponin?

  1. As a cleaning agent
  2.  As a neutraliser of insect bites
  3. As a dye for pigmentation and painting
  4. As an additive to food for flavouring and tenderising
Show Answers Only

\(A\)

Show Worked Solution
  • Saponin has both water-soluble and fat-soluble parts, allowing it to dissolve fats in water and act like a soap or detergent.
  • The fat-soluble side chain bonds with dirts and fats while the water soluble component bonds with the water molecules to form micelle.
  • The micelles can then be washed away leaving surfaces clean.

\(\Rightarrow A\)

CHEMISTRY, M7 EQ-Bank 21

With the use of a labelled diagram, describe how grease can be removed from fabric using soap.  (3 marks)

Show Answers Only

  • Soap molecules, as shown in the diagram, have a negatively charged (hydrophilic) “head” and a hydrophobic ‘tail’ consisting made up of fatty acids.
  • Hydrophobic tails are attracted to the grease particles and attach themselves. 
  • The hydrophilic heads, at the same time, are attracted to water molecules. This chain of attractions will lift grease off the fabric and suspend it in the water.
Show Worked Solution

  • Soap molecules, as shown in the diagram, have a negatively charged (hydrophilic) “head” and a hydrophobic ‘tail’ consisting made up of fatty acids.
  • Hydrophobic tails are attracted to the grease particles and attach themselves. 
  • The hydrophilic heads, at the same time, are attracted to water molecules. This chain of attractions will lift grease off the fabric and suspend it in the water.

CHEMISTRY, M7 2021 HSC 8 MC

Which diagram shows the expected arrangement of soap anions in an emulsion?
 

Show Answers Only

`D`

Show Worked Solution
  • Soap molecules contain a non-polar hydrophobic hydrocarbon tail and a polar hydrophilic head.
  • The non-polar tail forms dispersion forces with the oil molecule while the polar head forms ion-dipole forces with the polar water molecules.
  • The resulting orientation has the tail within the oil and the head group at the surface of the oil and water.

`=>D`