carboxylic acids and esters Flashcards
Alcohols can be used to prepare organic compounds with different functional groups.
HO(CH2)4OH can be oxidised to form HOOC(CH2)2COOH.
i. State the reagents and conditions and write an equation for this oxidation.
In the equation, use [O] for the oxidising agent. (3)
- K2Cr2O7 AND acid
AND reflux - HO(CH2)4OH + 4[O] → HOOC(CH2)2COOH + 2H2O
. The structural formula of compound A is shown below.
HOCHRCOOH
Two reactions of compound A are carried out.Suggest an equation for each reaction and state the type of reaction.
In your equations, draw structures for organic compounds.
You can use R for the alkyl group.
i. Magnesium ribbon is added to a solution of compound A.
Gas bubbles are seen and the magnesium slowly dissolves.
Equation
Type of
reaction (3)
- 2HOCH(R)COOH + Mg → (HOCH(R)COO)2Mg + H2
- redox
A student was provided with five compounds: an aldehyde, a ketone, a carboxylic acid and two
esters. The student decides to identify the type of compound by carrying out some chemical
tests.
Suggest chemical tests to identify the carboxylic acid and aldehyde.
For each test, include essential reagent(s), observation(s) and a balanced equation.
In your equations, use ‘R’ for the alkyl group.
i. Test for carboxylic acid (2)
Reagent and observation
sodium carbonate
AND
Fizzing/effervescence/bubbling ✓
Equation
Correctly balanced equation ✓
e.g. 2RCOOH + Na2CO3 → 2RCOONa + CO2 + H2O
. A student was provided with five compounds: an aldehyde, a ketone, a carboxylic acid and two
esters. The student decides to identify the type of compound by carrying out some chemical
tests.
Suggest chemical tests to identify the carboxylic acid and aldehyde.
For each test, include essential reagent(s), observation(s) and a balanced equation.
In your equations, use ‘R’ for the alkyl group
i. Test for aldehyde (2)
- Reagent and observation
Tollens’ (reagent)
AND
Silver (mirror) - Equation
RCHO + [O] → RCOOH
A student was provided with five compounds: an aldehyde, a ketone, a carboxylic acid and two
esters. The student decides to identify the type of compound by carrying out some chemical
tests.
Suggest chemical tests to identify the carboxylic acid and aldehyde.
For each test, include essential reagent(s), observation(s) and a balanced equation.
In your equations, use ‘R’ for the alkyl group
Suggest a chemical test to distinguish the ketone from the two esters (1)
2,4−dinitrophenylhydrazine
AND
Orange/yellow/red precipitate ✓
. The student wants to confirm that the other two compounds are esters. Unfortunately there is no
direct test for an ester group.
The esters are CH3COOC(CH3)3 and (CH3)3CCOOCH3.
Write an equation for the hydrolysis of one of the two esters with aqueous sodium
hydroxide.
Show the structures for the organic compounds (2)
- CH3COOC(CH3)3 + NaOH → CH3COONa + (CH3)3COH
- (CH3)3CCOOCH3 + NaOH → (CH3)3CCOONa + CH3OH
. The student wants to confirm that the other two compounds are esters. Unfortunately there is no
direct test for an ester group.
The esters are CH3COOC(CH3)3 and (CH3)3CCOOCH3.
The student plans the following:
* hydrolyse the two esters using aqueous sodium hydroxide.
* separate the hydrolysis products.
* carry out tests on the hydrolysis products.
Suggest a chemical test on the hydrolysis products that would allow the two esters to be
identified.
Write an equation for one reaction that takes place.
Show the structures for the organic compounds (2)
Reagent and observation
H+/Cr2O7
2− OR acidified (potassium/sodium) dichromate
AND
Orange to green (with CH3OH) ✓
Equation
CH3OH + [O] → HCHO + H2O
OR
CH3OH + 2[O] → HCOOH + H2O ✓
Stearic acid C17H35COOH
Sodium stearate is the salt formed when stearic acid reacts with sodium hydroxide solution.
Write an equation for the formation of sodium stearate. (1)
C17H35COOH + NaOH
→ C17H35COONa+ + H2O
Aqueous propanoic acid, C2H5COOH, reacts with carbonates and alkalis.
i. Write the full equation for the reaction of aqueous propanoic acid with sodium carbonate (1)
2C2H5COOH + Na2CO3 → 2C2H5COONa + CO2 + H2O
Aqueous propanoic acid, C2H5COOH, reacts with carbonates and alkalis.
Write the ionic equation for the reaction of aqueous propanoic acid with aqueous
potassium hydroxide (1)
H+ + OH− → H2O
Explain why bromine reacts more readily with salicylic acid than with benzene. (3)
lone pair / pair of electrons on O(H) / phenol is ∽ (partially)
delocalised into the ring
electron density increases / is high
Br2 / electrophile is (more) polarised
. How could the student measure the pH continuously as the NaOH(aq) is added? (1)
Using a pH probe on a data logger OR pH meter
in terms of
equilibrium, the colours of methyl red at low pH, at high pH, and at the end point of a
titration. You can use HA and A− in your explanation (3)
Explanation:
Acid / H+ reacts with A− AND equilibrium (position) shifts
towards HA (to give a red colour)
4
ALLOW direction of equilibrium shift if
6.1.3 Carboxylic Acids and Esters
PhysicsAndMathsTutor.com
Alkali / OH− reacts with HA/H+ AND equilibrium (position) shifts
towards A− (to give a yellow colour)
At end point, equal amounts of HA and A−
AND orange colour
Suggest how the hydroxide ion can act as a nucleophile (1)
i It is an electron pair donor OR donates a lone pair
Name the type of reaction of lactic acid with bases and with metals.
reaction with
bases:
reaction with
metals: (1)
i
reaction with bases: neutralisation
AND reaction with metals: redox
v. The addition polymer in (iii) is used widely in industry. Increasingly, waste polymers are
being processed as a more sustainable option than disposal.
Apart from recycling, state two methods for usefully processing waste polymers. (2)
combustion for energy production
use as an organic feedstock for the production of plastics and
other organic chemicals
i. Predict two reactions of lactic acid, each involving a different functional group.
Do not include reactions with bases or metals.
For each reaction,
state the type of reaction, the reagents and conditions
draw the structures of any organic products formed. (4)
i
v
Type of reaction of COOH: e.g. esterification
AND
reagents and conditions e.g. CH3OH AND H2SO4
Organic product of COOH reaction
Type of reaction of −OH AND reagents and conditions
Organic product of −OH reaction
e.g. product from CH3OH/H2SO4
→ CH3(CHOH)COOCH3
Many possible reactions of secondary
alcohol possible, e.g.
oxidation with K2Cr2O7 / H2SO4 + heat
→ CH3(CO)COOH
elimination with H2SO4 / H3PO4 + heat
→ CH2 = CHCOOH
esterification with CH3COOH / H2SO4 OR
CH3COCl → CH3(CHOOCCH3)COOH
bromination with NaBr / H2SO4
→ CH3(CHBr)COOH
