Option B Quiz

The formulas of three fatty acids are shown below:

stearic acid: CH₃(CH₂)₁₆COOH

oleic acid: CH₃(CH₂)₇CH=CH(CH₂)₇COOH

linoleic acid: CH₃(CH₂)₄(CH=CHCH₂)₂(CH₂)₆COOH

Identify which of these fatty acids is monounsaturated. [1 mark]

The formulas of three fatty acids are shown below:

stearic acid: CH₃(CH₂)₁₆COOH

oleic acid: CH₃(CH₂)₇CH=CH(CH₂)₇COOH

linoleic acid: CH₃(CH₂)₄(CH=CHCH₂)₂(CH₂)₆COOH

Explain which of the fatty acids has the highest melting point. [2 marks]

Answer explanation

Stearic acid has the highest melting point;

it has a linear structure allowing for stronger London dispersion forces with other molecules;

The structure of vitamin D is shown below.

Explain why vitamin D is a fat-soluble vitamin, even though it contains a polar hydroxyl (-OH) group. [1 mark]

Answer explanation

Vitamin D is fat-soluble since the majority of the structure contains nonpolar alkyl groups and ring structures; 

Proteins are polymers made from amino acid monomers.

a. i. Identify the two functional groups responsible for the amphoteric property of all amino acids. [1 mark]

Glycine can exist in three different structures at equilibrium in aqueous solution.

Identify which of these ions is the zwitterion and identify which one occurs in greatest concentration at high pH. [2 marks]

Answer explanation

Structure B is the zwitterion; structure C exists in highest concentration at high pH;

Determine the number of water molecules that were formed in the formation of this polypeptide. [1 mark]

• 1

• 2

• 3

• 0

Identify the three amino acids used to make this polypeptide, using section 33 of the data booklet. [1 mark]

Answer explanation

Leucine, alanine, glycine; 

HL:

A mixture of serine and alanine is analysed by chromatography, using ethanol as the solvent.

State and explain which amino acid travelled the furthest.

[2 marks]

Answer explanation

Serine travelled the furthest; serine is polar and is more soluble in the polar ethanol solvent.

Photosynthesis is the process for the synthesis of glucose by producers.

State a balanced chemical equation for the overall reaction for photosynthesis. [1 mark]

A glucose monomer can polymerise to form starch, cellulose or glycogen.

Predict which of the three glucose polymers would have the lowest solubility in water. [1 mark]