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B1.1.8—Hydrophobic properties of lipids

Lipids are mostly hydrophobic molecules with low oxygen-to-carbon ratios, making them insoluble in water and dependent on transport complexes in blood.

Syllabus
First assessment 2025
Objective
B1.1.8
Level
HL

Exam analysis

Chance of appearing2%of analysed past papers
Latest appearanceMay 2018
Most common paperPaper1
Typical marks1

Common command terms

  • Explain

Scoring notes

Common mistake
Calling oils insoluble without linking this to non-polar hydrocarbon chains and lack of hydrogen bonding.

Recent exam appearances

May 2018Paper1 ["HL"] · TZ16[ 1 ]B1.1.8—Hydrophobic properties of lipids
May 2017Paper1 ["HL"] · TZ25[ 1 ]B1.1.8—Hydrophobic properties of lipids
Practice this objective

Coverage 2017–2018 · Updated 15 Jul 2026

Non-Polar Lipids Avoid Water

Lipids are hydrophobic substances that dissolve in non-polar solvents but are only sparingly soluble in aqueous solvents.

Their structures contain large non-polar hydrocarbon regions that cannot form favourable interactions with water, so lipids cluster away from water or form separate phases.

Fats, oils, waxes, phospholipids and steroids are lipid examples. Lipids are grouped by solubility and hydrophobic behaviour rather than as one true polymer family built from repeating identical monomers.

Oil forms a separate layer on water but dissolves in a non-polar solvent because substances mix most readily when their intermolecular interactions are compatible.

Hydrophobic does not mean 'contains no oxygen' or 'is repelled by every substance'. Judge the whole molecule's polarity and its interaction with water.

Hydrophobic properties of lipids

Assessment in practice

1–4 marks
How it is assessed

This objective is assessed through multiple choice, commonly using Explain.

Command terms

Explain

What earns marks

Build the answer around this relationship: Lipids are generally hydrophobic because large parts of their molecules are non-polar.

Watch for

Calling oils insoluble without linking this to non-polar hydrocarbon chains and lack of hydrogen bonding.

Representative question

Question 1

[Maximum number: 1]

Which substance must be transported in the blood by lipoprotein complexes?

A

Cholesterol

B

Oxygen

C

Sodium chloride

D

Amino acids

Structure To Function

B1.1 becomes easy when every answer follows structure -> property -> function. Carbon skeletons and functional groups create molecular diversity. Condensation builds larger molecules and hydrolysis breaks them. Alpha-glucose stores energy as starch and glycogen; beta-glucose forms strong cellulose. Surface carbohydrates enable recognition. Lipids are hydrophobic, triglycerides store energy, phospholipids self-assemble into bilayers, and steroids cross membranes because they are mostly non-polar.

  • Carbon bonding and functional groups explain molecular diversity.
  • Condensation releases water; hydrolysis uses water.
  • Carbohydrates can store energy, build cell walls, and mark cell surfaces.
  • Lipids are hydrophobic and not true polymers.
  • Triglycerides store energy; phospholipids form membranes; steroids signal across membranes.

Concept essentials

  • Lipids are generally hydrophobic because large parts of their molecules are non-polar.
  • Oils do not form hydrogen bonds with water, while glucose can.
  • Steroids are lipids partly because they have a low oxygen-to-carbon ratio.
  • Cholesterol and fats are transported in blood within lipoprotein complexes.