Chemistry · Unit 15

Organic Chemistry

The chemistry of carbon

Carbon forms four bonds and bonds strongly to itself, and those two facts generate more compounds than the rest of the periodic table combined.

The unit covers hydrocarbons and crude oil, alkanes and alkenes, functional groups as the organising idea, polymers, and the main reaction types.

This unit breaks down into 20 short steps and 120 questions, starting at difficulty 1 and building to 3. Below you can see exactly what it covers, how the path is structured, and worked examples with explanations.

Steps: 20
Questions: 120
Difficulty: 1-3

What this unit covers

Hydrocarbons and Crude Oil
Alkanes and Alkenes
Functional Groups
Polymers
Organic Reactions

Where this fits

Needs Chemical Bonding. Largely self-contained after that.

Where people slip

Reactivity follows the functional group, not the chain length. Once you can spot the group, you can predict the chemistry of a molecule you have never seen.

How the unit is structured

Organic Chemistry runs as 20 short steps that unlock in order. 15 are practice rounds and 5 are challenge rounds that pull together everything before them. Questions start at difficulty 1 and climb to 3 as you progress.

Step 1 · easierStep 20 · harder

Challenge rounds

Example questions

30 real questions from this unit, with the answer and the reason behind it, grouped by what they practise. There are 120 in the unit altogether.

Alkanes and Alkenes

Build the sentenceLevel 2
1. Put the words in order to make a true statement about ethene.
Answer: Ethene is an unsaturated hydrocarbon
Ethene contains a C=C double bond, so it is an unsaturated hydrocarbon.
Fact or fibLevel 2
2. Bromine water turns from orange-brown to colourless when it is shaken with an alkene.
Answer: True
Alkenes decolourise bromine water because the double bond reacts with it, while alkanes do not.
Fill the blankLevel 2
3. A family of compounds with the same general formula and similar chemical properties is called a ____ series.
- homologouscorrect
- periodic
- transition
- reactive
The alkanes are one example of a homologous series.
Match the pairsLevel 2
4. Match each alkane to its chemical formula.
Answer: Methane = CH4; Ethane = C2H6; Propane = C3H8; Butane = C4H10
Each alkane in the series follows the pattern CnH2n+2.
Choose all that applyLevel 3
5. Which statements about alkenes are correct? Select all that apply.
- they are unsaturated hydrocarbonscorrect
- they contain a carbon-carbon double bondcorrect
- they have the general formula CnH2n+2
- they are fully saturated
Alkenes are unsaturated hydrocarbons containing a C=C double bond; they are not fully saturated and do not follow the CnH2n+2 formula.
Guess the numberLevel 3
6. How many structural (chain) isomers does the alkane C4H10 have?
Answer: 2 isomers
C4H10 has two chain isomers: butane (straight chain) and 2-methylpropane (branched).

Functional Groups

Guess the numberLevel 1
7. How many carbon atoms are there in one molecule of ethanol, C2H5OH?
Answer: 2 carbon atoms
The formula C2H5OH shows two carbon atoms.
Multiple choiceLevel 1
8. Ethanol belongs to which family of organic compounds?
- Alcoholscorrect
- Alkanes
- Alkenes
- Acids
Ethanol contains an -OH group, so it is a member of the alcohols.
Match the pairsLevel 2
9. Match each functional group to the class of compound it defines.
Answer: -OH = alcohol; -COOH = carboxylic acid; -CHO = aldehyde; -NH2 = amine
Each functional group identifies a homologous series: -OH alcohols, -COOH carboxylic acids, -CHO aldehydes, -NH2 amines.
Choose all that applyLevel 3
10. Which of these compounds contain a carbonyl (C=O) group? Select all that apply.
- propanalcorrect
- propanonecorrect
- propan-1-ol
- propane
Aldehydes (propanal) and ketones (propanone) both contain a C=O carbonyl group, whereas an alcohol and an alkane do not.
Fact or fibLevel 3
11. Fact or fib: ketones give a positive result with both Tollens' reagent and Fehling's solution.
Answer: False
Ketones cannot be easily oxidised, so they give a negative result with both tests; only aldehydes react, which is how the tests tell them apart.
Fill the blankLevel 3
12. The carbonyl carbon in an aldehyde or ketone is slightly positive, so it is attacked by ____ in an addition reaction.
- nucleophilescorrect
- electrophiles
- free radicals
- cations
The electronegative oxygen makes the carbonyl carbon delta positive, so electron-rich nucleophiles attack it in nucleophilic addition.

Hydrocarbons and Crude Oil

Fill the blankLevel 1
13. Crude oil is separated into useful fractions by fractional ____.
- distillationcorrect
- filtration
- crystallisation
- chromatography
Fractional distillation separates crude oil into fractions with similar boiling points.
Multiple choiceLevel 1
14. Hydrocarbons are compounds that are made from only which two elements?
- Hydrogen and carboncorrect
- Hydrogen and oxygen
- Carbon and oxygen
- Carbon and nitrogen
A hydrocarbon contains atoms of only hydrogen and carbon and nothing else.
Picture questionLevel 1
15. ✈️ Aircraft are powered by fuel from which crude oil fraction?
- Kerosenecorrect
- Bitumen
- Refinery gas
- Petrol
Kerosene is the fraction used as jet fuel for aircraft.
Match the pairsLevel 2
16. Match each crude oil fraction to what it is mainly used for.
Answer: Petrol = Fuel for cars; Diesel = Fuel for lorries; Bitumen = Surfacing roads; Refinery gas = Bottled gas for cooking
Each fraction has typical uses that depend on the size of its molecules.
Put in orderLevel 2
17. Put these crude oil fractions in order, from the top of the fractionating column (lowest boiling point) to the bottom (highest boiling point).
Answer: Refinery gas -> Petrol -> Kerosene -> Diesel -> Bitumen
Fractions leave the column in order of boiling point, with refinery gas at the top and bitumen at the bottom.
Choose all that applyLevel 3
18. Which statements about the structure of benzene, C6H6, are correct? Select all that apply.
- All six carbon-carbon bonds are the same lengthcorrect
- The molecule is planar (flat)correct
- Every C-C-C bond angle is 120 degreescorrect
- It has three short double bonds and three longer single bonds
Benzene is a flat, regular hexagon in which all six carbon-carbon bonds are identical in length (between a single and a double bond) and every bond angle is 120 degrees.

Organic Reactions

Choose all that applyLevel 2
19. Which TWO substances are produced when a hydrocarbon burns completely in plenty of oxygen?
- Carbon dioxidecorrect
- Watercorrect
- Carbon monoxide
- Soot (carbon)
Complete combustion of a hydrocarbon produces only carbon dioxide and water.
Build the sentenceLevel 3
20. Build the sentence that describes how alkenes react with electrophiles.
Answer: Electrophilic addition adds atoms across the double bond
In electrophilic addition, atoms add across the C=C double bond, turning an unsaturated molecule into a saturated one.
Fact or fibLevel 3
21. Fact or fib: heating a halogenoalkane with an excess of ammonia in ethanol produces a primary amine.
Answer: True
Ammonia acts as a nucleophile and substitutes the halogen; using excess ammonia favours the primary amine over further substitution.
Fill the blankLevel 3
22. Heating a primary alcohol under reflux with excess acidified potassium dichromate(VI) oxidises it all the way to a ____.
- carboxylic acidcorrect
- ketone
- aldehyde
- ester
Reflux with excess oxidising agent takes a primary alcohol past the aldehyde stage to a carboxylic acid.
Guess the numberLevel 3
23. How many chiral (asymmetric) carbon atoms are there in a molecule of lactic acid, CH3CH(OH)COOH?
Answer: 1 chiral carbons
The central carbon is bonded to CH3, OH, H and COOH, four different groups, so lactic acid has exactly one chiral centre.
Match the pairsLevel 3
24. Match each carbonyl compound reduced by NaBH4 to the alcohol it forms.
Answer: Ethanal + NaBH4 = Ethanol; Propanal + NaBH4 = Propan-1-ol; Propanone + NaBH4 = Propan-2-ol; Butanone + NaBH4 = Butan-2-ol
NaBH4 reduces aldehydes to primary alcohols and ketones to secondary alcohols by adding hydrogen across the C=O bond.

Polymers

Multiple choiceLevel 1
25. The small molecules that join together to make a polymer are called what?
- Monomerscorrect
- Isotopes
- Ions
- Fractions
Many monomer molecules join together to form a long polymer chain.
Picture questionLevel 1
26. 🛍️ This thin, flexible carrier bag is most likely made from which polymer?
- Poly(ethene)correct
- Ethanol
- Bitumen
- Kerosene
Carrier bags are usually made from poly(ethene), a cheap and flexible plastic.
Build the sentenceLevel 2
27. Put the words in order to describe how a polymer forms.
Answer: Many monomers join to make a polymer
A polymer is built up when many small monomer molecules join together.
Fill the blankLevel 2
28. Ethene molecules join together to form poly(ethene) in a reaction called ____ polymerisation.
- additioncorrect
- condensation
- fractional
- neutralisation
In addition polymerisation, monomers with a C=C double bond add together with no other product formed.
Odd one outLevel 2
29. Which of these is the odd one out because it is a small monomer, not a polymer?
- Ethenecorrect
- Poly(ethene)
- Poly(propene)
- PVC
Ethene is a single small monomer, while the others are long-chain polymers.
Match the pairsLevel 3
30. Match each alkene monomer to the addition polymer it forms.
Answer: ethene = poly(ethene); chloroethene = poly(chloroethene); propene = poly(propene); tetrafluoroethene = poly(tetrafluoroethene)
Addition polymers are named from their monomer: the monomer's C=C opens up and repeats to build the chain.

Where these questions come from. Each unit starts as a plan of the concepts it should cover and the difficulty it should span. Questions are written against that plan with AI assistance, then checked by a validator that rejects anything without a single defensible answer, an explanation, or plausible wrong options. How we write questions sets out the whole process, and corrections are fixed in the bank and reach the site and the app the same day.

How you practise

This unit mixes 17 different question formats, so you are recalling and applying rather than recognising the same layout every time.

Build the sentence
Choose all that apply
Fact or fib
Fill the blank
Guess the number
Listen and choose
Match the pairs
Multiple choice
Odd one out
Picture question
Put in order
Sequence recall
Sort into groups
Spell it
Tap the pairs
True or false
Type the answer

Practise Organic Chemistry

120 questions across 20 steps. Start with step one and crawl at your own pace.

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