The shape of the lesson
By the end of the lesson, learners can
- Ethanoic acid as an acid: Compare ethanoic acid with hydrochloric acid of the same concentration in the simulator.
- Making ethanoic acid: Extended.
- Esters and their names: Extended.
- Ethanoic acid: weak acid; metal, base, carbonate give ethanoates.
- Extended, oxidation: acidified KMnO4 (purple to colourless) or bacteria in air.
- Extended, esterification: acid + alcohol ⇌ ester + water, conc. H2SO4 catalyst.
- Naming: alcohol part first (ethyl), acid part second (ethanoate).
One picture every idea returns to
Carboxylic acids contain the –COOH functional group; ethanoic acid is CH3COOH. Ethanoic acid is a weak acid: it reacts with metals to give a salt and hydrogen, with bases to give a salt and water, and with carbonates to give a salt, water and carbon dioxide. Its salts are ethanoates. Extended: ethanoic acid is made by oxidising ethanol, either with acidified aqueous potassium manganate(VII) or by bacterial oxidation during vinegar production. A carboxylic acid reacts with an alcohol in the presence of an acid catalyst to form an ester and water: ethanoic acid + ethanol ⇌ ethyl ethanoate + water.
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, The sour taste of vinegar.. Ethanoic acid is the acid in vinegar. 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: Ethanoic acid as an acid | Compare ethanoic acid with hydrochloric acid of the same concentration in the simulator. Project tab 2 of the lab (Carboxylic acids lab, how acidic, and why) and let a student drive it while the class predicts. | Whole class, then pairs |
| 13 to 21 min | Teach and check: Making ethanoic acid | Extended. Project tab 3 of the lab (Hydroxy compounds lab, oxidation) and let a student drive it while the class predicts. | Pairs |
| 21 to 30 min | Teach and check: Esters and their names | Extended. Project tab 3 of the lab (Carboxylic acids lab, making an ester) and let a student drive it while the class predicts. | Jot Thoughts |
| 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 Esters and their names, 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.
Jot Thoughts
Teams write ideas on slips, one idea per slip, as many as they can in two minutes, saying each aloud as they place it in the middle. Then they sort the slips, which is where the structure of the topic appears.
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 |
|---|---|
| In an ester name the alcohol part comes first (ethyl, methyl) and the acid part second (ethanoate, propanoate), even though the formula CH 3 COOC 2 H 5 is written acid part first. | Methanol + ethanoic acid gives methyl ethanoate, not ethyl methanoate. Ethanoic acid is weak because it is only partly dissociated, not because it is dilute: weak and dilute mean different things. |
Carboxylic acids and esters: worksheet
6 questions, 14 marks. Written in the style of the papers; no past paper question is reproduced.
Write a word equation and a balanced equation for the reaction between ethanoic acid and sodium hydroxide.
Ethanoic acid is added to sodium carbonate. Describe what is seen and name the gas produced.
Explain why ethanoic acid is classed as a weak acid, and how its pH compares with hydrochloric acid of the same concentration.
(Extended) Describe two ways of converting ethanol into ethanoic acid.
(Extended) Ethanol reacts with ethanoic acid when warmed with a few drops of concentrated sulfuric acid. Write the equation, name the organic product and state the role of the sulfuric acid.
(Extended) Name the esters formed from (a) methanol and ethanoic acid, (b) ethanol and propanoic acid.
Answer key and marking notes
- ethanoic acid + sodium hydroxide → sodium ethanoate + water
- CH3COOH + NaOH → CH3COONa + H2O
- Fizzing (effervescence) as the solid dissolves.
- Carbon dioxide (turns limewater milky).
- It is only partially dissociated (ionised) in water, so few H+ ions are released.
- Its pH is higher than that of hydrochloric acid of the same concentration.
- Warm ethanol with acidified aqueous potassium manganate(VII).
- The solution changes from purple to colourless.
- Bacterial oxidation: leave ethanol solution (such as wine) exposed to air so bacteria oxidise it to vinegar.
- CH3COOH + C2H5OH ⇌ CH3COOC2H5 + H2O
- Product: ethyl ethanoate (an ester).
- Sulfuric acid is a catalyst.
- (a) methyl ethanoate.
- (b) ethyl propanoate.
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.
Magnesium ribbon is added to aqueous ethanoic acid. Which products form?
- Amagnesium ethanoate and hydrogen
- Bmagnesium ethanoate and water
- Cmagnesium ethanoate and carbon dioxide
- Dmagnesium oxide and ethanol
Sodium carbonate is added to ethanoic acid. What is observed, and which salt forms?
- Afizzing; sodium ethanoate
- Bfizzing; sodium carbonate ethanoate
- Cno reaction, because ethanoic acid is organic
- Da white precipitate; sodium ethanol
What is the formula of the salt formed when ethanoic acid is neutralised by sodium hydroxide?
- ACH3COONa
- BCH3CH2ONa
- CNaCOOH
- DCH3COOH2Na
Which is the functional group and the name of the carboxylic acid with two carbon atoms?
- A−COOH; ethanoic acid
- B−OH; ethanol
- C−COOH; methanoic acid
- DC=C; ethene
A student adds calcium carbonate to aqueous ethanoic acid and passes the gas into limewater. What is seen?
- Athe limewater turns milky
- Bthe limewater stays clear and the gas pops with a lighted splint
- Cthe limewater turns orange
- Dno gas is given off
Ethanol is warmed with acidified aqueous potassium manganate(VII). Which is correct?
- Athe solution changes from purple to colourless and ethanoic acid forms
- Bthe solution changes from colourless to purple and ethene forms
- Cthe solution changes from orange to green and ethyl ethanoate forms
- Dthere is no change because ethanol cannot be oxidised
The diagram shows an ester. What is its name, and which alcohol and acid is it made from?
- Amethyl propanoate, from methanol and propanoic acid
- Bpropyl methanoate, from propanol and methanoic acid
- Cethyl ethanoate, from ethanol and ethanoic acid
- Dmethyl ethanoate, from methanol and ethanoic acid
Aqueous ethanoic acid and hydrochloric acid of the same concentration are compared. The ethanoic acid has a higher pH and reacts more slowly with magnesium. Why?
- Aethanoic acid is a weak acid, so it is only partially ionised and the concentration of H+ ions is lower
- Bethanoic acid is a strong acid but is more dilute
- Cethanoic acid contains no hydrogen ions at all
- Dethanoic acid is an alkali
Quiz key
Acid + metal → salt + hydrogen, so magnesium and ethanoic acid give magnesium ethanoate and hydrogen. Water is formed with a base, and carbon dioxide only with a carbonate. Magnesium oxide and ethanol are not formed: the acid is not reduced to an alcohol.
Ethanoic acid reacts with sodium carbonate to give sodium ethanoate, water and carbon dioxide, which is seen as fizzing (effervescence). The salt of ethanoic acid is an ethanoate, so sodium carbonate ethanoate is not a real compound. Ethanoic acid is an acid and reacts like one, even though it is organic. Sodium ethanoate is soluble, so there is no precipitate, and 'sodium ethanol' is not a salt.
CH3COOH + NaOH → CH3COONa + H2O. The acidic hydrogen of the −COOH group is replaced by Na, giving sodium ethanoate. CH3CH2ONa comes from ethanol, not ethanoic acid. NaCOOH has lost the CH3 group. CH3COOH2Na keeps the hydrogen that should have been replaced and adds an extra one.
Carboxylic acids have the −COOH group, and the two-carbon acid CH3COOH is ethanoic acid. −OH and ethanol describe an alcohol. Methanoic acid, HCOOH, has only one carbon. C=C and ethene describe an alkene.
Ethanoic acid reacts with calcium carbonate to give calcium ethanoate, water and carbon dioxide, and carbon dioxide turns limewater milky. A squeaky pop is the test for hydrogen, which forms with metals, not carbonates. Limewater does not turn orange. A gas is given off, because ethanoic acid reacts with carbonates like any other acid.
Acidified potassium manganate(VII) oxidises ethanol to ethanoic acid, and the purple manganate(VII) is reduced, so the solution turns colourless. The colour change is not the reverse, and forming ethene would be dehydration, not oxidation. Orange to green is the colour change of acidified dichromate, and an ester needs an acid and an alcohol. Ethanol is oxidised easily, which is also how vinegar forms by bacterial oxidation.
The acid part is CH3CH2C(=O)−, three carbons including the C=O carbon, from propanoic acid. The group on the other oxygen is CH3, from methanol. So the ester is methyl propanoate. Propyl methanoate reverses the two parts. Ethyl ethanoate has the same molecular formula, C4H8O2, but two carbons on each side. Methyl ethanoate miscounts the acid chain by forgetting the C=O carbon.
Ethanoic acid is a weak acid: only a small fraction of its molecules ionise to give H+ ions, so at the same concentration it has fewer H+ ions than fully ionised hydrochloric acid. That gives a higher pH and a slower reaction. The concentrations are stated to be the same, so dilution is not the reason. Ethanoic acid does form some H+ ions, which is why it reacts at all. It is an acid, not an alkali.
What to project
The student lesson embeds these tabs. Open them full screen on the projector; every slider has a drag handle on the stage.
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.