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Find the functional group: alcohol or acid

Use a 3D pen to draw C, O and H atom nodes and two removable markers. Assemble ethane from the same parts, change it into ethanol and then ethanoic acid by replacing only the second carbon node. Place a ring around -OH and a frame around the whole -COOH group, write the formulae and names, and identify the groups in four new formulae.

Age
13–15 years
Length
approx. 45 min
Level
Medium
Where you teach
School
Purpose
Educational
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How to run this session

Stages and timing
  1. Two carbon nodes: CH3 and CH2
  2. Socket check and C=O carbon
  3. OH group and end hydrogen
  4. Ring, frame and cooling
  5. Ethane, then ethanol
  6. The same OH group in an acid
  7. Ring inside frame and pair comparison
  8. Check yourself: four new formulae
  9. For faster finishers: methanol

What gets built

After the lesson, identify the hydroxyl group -OH (alcohol) and the carboxyl group -COOH (carboxylic acid) in a formula. Explain why -OH within -COOH does not make the compound an alcohol. Write the condensed structural and molecular formulae of ethanol (CH3-CH2-OH, C2H6O; grouped notation C2H5OH) and ethanoic acid (CH3-COOH, C2H4O2), give their names and draw the acid's structural formula with a C=O bond.

What it practises
  • Identify hydroxyl -OH and carboxyl -COOH groups in condensed structural formulae.
  • Write ethanol and ethanoic acid formulae and names, with the C=O bond and both oxygen atoms; explain the -OH/-COOH difference.
  • Count bonds for C (4), O (2) and H (1), and trace detachable PLA parts over a 1:1 pattern.

Success criteria
  • The five nodes, ring and frame lie separately, and the tab enters the socket without force.
  • The same parts form ethane, ethanol with a ring and the acid with a ring inside its frame on W2.
  • W2 contains the formulae and names of both compounds and the acid's structural formula with a double bond.
  • Identify the groups in four new formulae and explain why OH inside the frame does not indicate an alcohol.

What you need
Filament
PLA
Colours
colour shown in the illustration
Also
1.4 m of PLA filament per pupil (one colour, no filament changes), 3D pen with stand (one per pupil), transparent mat, W1 - 1:1 pattern for nodes, ring and frame (pack printout, print at 100 %), W2 - alcohol / acid fields and record card (pack printout, landscape A4, print at 100 %), pencil, ruler (one per pair)

Files

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Version 6cb0bdee-2635-4504-be46-6a132554772e Updated 2026-10-12

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