MYP Chemistry: Organic Chemistry & Hydrocarbons FAQ

Typical MYP 4-5 organic content, mapped against the MYP: Sciences guide structure of Knowing and Understanding, Inquiring and Investigating, Processing and Evaluating, and Reflecting on the Impacts of Science:

1. Carbon's bonding — four covalent bonds, why it forms long chains
2. Alkanes CnH2n+2 — naming methane to hexane, drawing structural/skeletal formulae
3. Alkenes CnH2n — the C=C double bond, why they're more reactive
4. Isomerism — same formula, different structure (e.g. butane vs 2-methylpropane)
5. Combustion — complete vs incomplete, and why incomplete combustion produces carbon monoxide
6. Fractional distillation — how crude oil is separated by boiling point

Quick tip: examiners mark structural formulae, not just molecular formulae — CH4 alone won't score full marks where a diagram is asked for.

Quick comparison:

The bromine water test is the one examiners love in a practical write-up question — describe the colour change, not just the result.

Worked example: Name the hydrocarbon C5H10.

1. Count the carbons: 5 → prefix is "pent-"
2. Check the formula against CnH2n+2 (alkane) or CnH2n (alkene): 2(5)=10, matches CnH2n
3. So it's unsaturated → suffix "-ene"
4. Answer: pentene

Common mistake: students memorise the prefixes but forget to check saturation first, and default to "-ane" even when the hydrogen count doesn't fit.

Why examiners care: two molecules can have almost identical hydrocarbon skeletons but completely different chemical behaviour once you swap in a functional group. Ethane (C2H6) is fairly unreactive; ethanol (C2H5OH) burns cleanly, reacts with sodium, and is what's fermented in brewing. That contrast is a favourite short-answer question.

Quick tip for a Criterion A (Knowing and Understanding) response: don't just say "carbon bonds a lot" — name the property (catenation), state the electron count (4 valence electrons), and link it to structural diversity (chains, branches, rings) for full marks.

3 things to check before you submit any organic structure question:

1. Has every carbon got exactly four bonds shown or implied?
2. Did the question say "draw" (needs a diagram) or "state the formula" (text is fine)?
3. Have you matched the general formula (CnH2n+2 or CnH2n) to check your own answer before moving on?

Criterion D often shows up here specifically because hydrocarbons connect naturally to real-world impact questions — fossil fuel combustion, climate change, or plastics from cracking. If your unit includes a Criterion D task, expect to justify a scientific claim about hydrocarbon use with data, not just describe the chemistry.

A five-minute daily drill that works:

1. Write down a random carbon count (1-6)
2. Draw both the alkane and alkene versions
3. Name each one
4. Check every carbon has four bonds
5. Swap in an -OH group on one carbon and rename it as an alcohol

Students who do this for even five days before a test consistently stop losing marks on "draw the structural formula of…" questions — it's mechanical practice, not a conceptual gap, for most of them.

This unit is also where fractional distillation gets introduced — the industrial process separating crude oil into fractions (petrol, diesel, bitumen) by boiling point. It's a favourite MYP diagram question, and it reappears, in more depth, in DP Chemistry's organic chemistry topic.

Where DP goes further: reaction mechanisms (substitution, addition, elimination), a much wider range of functional groups (esters, amines, amides), and quantitative analysis using infrared spectroscopy and mass spectrometry. Students who arrive at DP shaky on naming alkenes or drawing isomers lose time in the first term catching up rather than learning new content — worth nailing MYP 4-5 naming properly rather than skimming it.

If your unit does cover it, the key idea examiners want is addition polymerisation: many small unsaturated monomer molecules joining end-to-end because the C=C double bond opens up to form new single bonds. You're not expected to draw full polymer mechanisms at MYP level — that's DP territory.

Organic chemistry is one of the more visual, drawing-heavy topics in MYP Chemistry, so worksheets with structure-drawing practice tend to help more than flashcards here. Topical Worksheets and Revision Notes on RevisionPrep are built around exactly this kind of criterion-mapped practice, letting your child self-check against MYP Sciences criteria without needing you to know the chemistry yourself.