The shape of the lesson
By the end of the lesson, learners can
- Polyamides and polyesters: Extended.
- Addition or condensation?: Extended.
- Proteins, nature's polyamides: Extended.
- Nylon: diacid + diamine, amide link –CONH–, polyamide.
- PET: diacid + diol, ester link –COO–, polyester; recyclable to monomers.
- Condensation vs addition: water released vs polymer only.
- Proteins: amino acids, amide links; hydrolysis gives amino acids back.
One picture every idea returns to
Extended. In condensation polymerisation two different functional groups react to form a link and a small molecule, usually water, is released each time. Nylon is a polyamide made from a dicarboxylic acid and a diamine; the monomers join by amide linkages, –CONH–. PET is a polyester made from a dicarboxylic acid and a diol; the monomers join by ester linkages, –COO–. PET can be converted back into its monomers and re-polymerised, so it can be recycled. Proteins are natural polyamides made from amino acids, H2N–CHR–COOH, joined by the same amide link; hydrolysis breaks them back into amino acids.
Forty-five minutes, phase by phase
| Time | Phase | What happens in the room | Grouping |
|---|---|---|---|
| 0 to 5 min | Hook: predict | Open with the question in the title, Linking chains by losing water.. Nylon in ropes, PET in drinks bottles and the proteins in your muscles are all built the same way: two functional groups react, a small molecule of water is released, and a link forms. Put the figure on the board: it is the one picture every idea in the lesson returns to. | Whole class, then pairs |
| 5 to 13 min | Teach and check: Polyamides and polyesters | Extended. | Whole class, then pairs |
| 13 to 21 min | Teach and check: Addition or condensation? | Extended. | Pairs |
| 21 to 30 min | Teach and check: Proteins, nature's polyamides | Extended. | Think-Pair-Share |
| 30 to 36 min | Check | The four Stage 1 questions from the student lesson, answered on mini whiteboards or by show of fingers. Re-teach the one most get wrong. | Individual, then whole class |
| 36 to 43 min | Plenary | The exam-style questions from Stage 2, one at a time: thirty seconds alone, then a random call. The feedback lines in the key give the examiner's wording. | Individual, random call |
| 43 to 45 min | Exit and homework | Set the worksheet below (6 questions, 14 marks). Learners self-assess against the objectives before they leave. | Individual |
Protect the parts that carry the learning
The sequence carries about fifty minutes of material, so the lab is driven by one student while the class predicts rather than explored freely. Times are a guide.
Protected: the check at 30 minutes. It is the only individual read on whether the key idea landed, and it is not cut.
Cut first if the build overruns: the last check in Proteins, nature's polyamides, never the check or the plenary.
In a 60 minute block: run worksheet questions 1 to 3 in class as a Rally Coach set and model both the hardest worked example and its check live.
Think-Pair-Share
Pose the question, give thirty seconds of silent thinking, then a minute to compare with a partner before a few pairs share with the class. The silent minute is the part that cannot be cut.
The full structure, with its variations and the other twelve, is on the cooperative-learning page.
What to head off, and how
| Trap learners fall into | Teaching move that pre-empts it |
|---|---|
| The amide link is –CO–NH– and the ester link is –CO–O–: check whether the atom after the C=O is N or O. | In a repeat unit, the water has already gone, so do not leave –OH or –H on the ends of the bracketed unit. Hydrolysis is the reverse of condensation: water is used, not released. |
Condensation polymers and proteins: worksheet
6 questions, 14 marks. Written in the style of the papers; no past paper question is reproduced.
(Extended) Name the two types of monomer used to make nylon and the type of linkage formed.
(Extended) The monomers HOOC–□–COOH and HO–▢–OH form a polymer. Draw (or write) its repeat unit and state the type of polymer.
(Extended) Give three differences between addition polymerisation and condensation polymerisation.
(Extended) Give the general structure of an amino acid and name the linkage that joins amino acids in a protein.
(Extended) A protein is heated with hydrochloric acid. Describe what happens and how the products could be identified.
(Extended) Explain why PET is easier to recycle into new PET than many other plastics.
Answer key and marking notes
- A dicarboxylic acid and a diamine.
- Amide linkage, –CO–NH–.
- –[CO–□–CO–O–▢–O]–
- A polyester (such as PET).
- Addition uses alkene monomers with C=C bonds; condensation uses monomers with two functional groups.
- Addition gives only the polymer; condensation also gives a small molecule such as water.
- Addition polymers have only C–C bonds in the chain; condensation polymers have amide or ester linkages.
- H2N–CHR–COOH (an amine group and a carboxylic acid group).
- Amide (peptide) linkage, –CO–NH–.
- The protein is hydrolysed: water breaks the amide links.
- The products are amino acids.
- They are separated by chromatography and made visible with a locating agent; Rf values are compared with known amino acids.
- PET can be broken down (by hydrolysis) back into its monomers.
- The monomers can be purified and polymerised again to make new PET of the same quality.
8 multiple-choice questions on this lesson
From the topic question bank. Assign them in the app for a marked score in your gradebook, or run the topic as a class game.
What type of polymer is nylon?
- Aa polyamide made by condensation polymerisation
- Ba polyester made by addition polymerisation
- Ca polyalkene made by addition polymerisation
- Da natural protein
What small molecule is usually formed when a polyester or polyamide is made?
- Awater
- Bhydrogen
- Ccarbon dioxide
- Dethene
Which pair of monomers forms a polyester such as PET?
- Aa dicarboxylic acid and a diol
- Ba dicarboxylic acid and a diamine
- Can alkene and an alcohol
- Damino acids only
Proteins are natural polymers. Which monomers form proteins, and what is the linkage?
- Aamino acids; amide linkage
- Bglucose; ester linkage
- Camino acids; ester linkage
- Dethene; C−C single bonds
Which is an advantage of PET over many other plastics?
- Ait can be converted back into its monomers and repolymerised
- Bit is biodegradable in a few days
- Cit is made by addition polymerisation with no waste
- Dburning it produces only water
A section of a polymer chain is −CO−C6H4−CO−NH−(CH2)6−NH−CO−. Which linkage is present, and what type of polymer is it?
- Aamide linkage; a polyamide
- Bester linkage; a polyester
- Camide linkage; an addition polymer
- DC=C linkage; a polyalkene
Which pair of monomers can react together to make a polyamide?
- AHOOC−C6H4−COOH and H2N−(CH2)6−NH2
- BHOOC−C6H4−COOH and HO−CH2CH2−OH
- CCH3COOH and CH3NH2
- DCH2=CH2 and CH2=CHCl
A protein is heated with concentrated hydrochloric acid for several hours. What happens?
- Athe amide linkages are hydrolysed and the protein is broken down into amino acids
- Bthe protein polymerises further into a longer chain
- Cthe protein is cracked into alkanes and alkenes
- Dthe ester linkages are broken to give a diol and a dicarboxylic acid
Quiz key
Nylon is a polyamide: its monomers are joined by amide linkages, −CONH−, with water lost each time, so it is a condensation polymer. A polyester has ester linkages, and PET is the polyester example. Addition polymers such as poly(ethene) come from alkenes. Nylon is synthetic, although proteins share its amide linkage.
In condensation polymerisation each new linkage forms with the loss of a small molecule, which for PET and nylon is water (H from one monomer and OH from the other). Hydrogen, carbon dioxide and ethene are not lost in these reactions.
A polyester forms from a dicarboxylic acid (two −COOH groups) and a diol (two −OH groups), so an ester linkage forms at each end. A dicarboxylic acid and a diamine give a polyamide such as nylon. An alkene and an alcohol do not form a polyester. Amino acids join to give proteins, which are polyamides.
Proteins are made from amino acid monomers joined by amide (peptide) linkages, −CONH−, with water lost each time. Glucose forms starch, and its linkage is not an ester. Amino acids do not join by ester linkages. Ethene forms poly(ethene), an addition polymer.
PET can be broken down (hydrolysed) back into its monomers, which can then be repolymerised into new PET, a form of recycling. PET is not rapidly biodegradable. It is a condensation polymer, so water is lost as it forms. Burning it produces carbon dioxide as well as water.
The units are joined by −CO−NH−, which is an amide linkage, so this is a polyamide (a nylon), made by condensation. An ester linkage would be −CO−O−, with no nitrogen. Polyamides are condensation polymers, not addition polymers. There is no C=C linkage in the chain.
A dicarboxylic acid and a diamine each have two reactive groups, so amide linkages form at both ends and a long chain grows. A dicarboxylic acid and a diol form a polyester. Ethanoic acid and methylamine each have only one reactive group, so they form one amide molecule, not a polymer. Ethene and chloroethene form addition polymers.
Hydrolysis breaks each amide linkage by adding water back, so the protein is broken into its amino acid monomers, which can then be identified by chromatography. Acid hydrolysis breaks chains; it does not make them longer. Cracking applies to hydrocarbons. Proteins have amide linkages, not ester linkages, and amino acids, not diols and dicarboxylic acids, are formed.
Slides for this lesson
A projectable deck for every pack is on the way. Until then, present the student lesson full screen: its sections, figure and lab tabs follow the same order as the plan above.