Mr Cole Chemistry

Introduction to Carboxylic Acids

Intro to Carboxylic Acids

Carboxylic Acids Worksheet

1. Drawing Molecules & Isomers

1. Draw the following molecules:
a) Propanoic acid
Propanoic acid structure Propanoic acid structure 2
b) 2-hydroxyethanoic acid
2-hydroxyethanoic acid structure 2-hydroxyethanoic acid structure 2
c) But-3-enoic acid
But-3-enoic acid structure But-3-enoic acid structure 2
d) Ethanedioic acid
Ethanedioic acid structure Ethanedioic acid structure 2
2. Draw a skeletal formula for the following molecules:
a) A functional group isomer of ethanoic acid.
Functional group isomer 1 Functional group isomer 2
b) A positional isomer of 1-hydroxypropanoic acid.
Positional isomer
c) A stereoisomer of but-2-enoic acid.
Stereoisomer 1 Stereoisomer 2
d) Both stereoisomers of 2-hydroxypropanoic acid (3D representations).
Stereoisomers of 2-hydroxypropanoic acid

(Note: Skeletal formulas are not typically used for 3D optical isomers).

3. Draw a diagram representing the interaction between water molecules and ethanoic acid molecules when ethanoic acid is dissolved in water.
Interaction Diagram 1 Interaction Diagram 2

2. Reactions as Acids

4. Ethanoic acid is a weak acid.
a) Write an equation that shows ethanoic acid is an acid.
Dissociation of ethanoic acid
b) Write a symbol equation and an ionic equation for: Ethanoic acid reacting with sodium hydroxide.

CH₃COOH + NaOH → CH₃COO⁻Na⁺ + H₂O

H⁺ + OH⁻ → H₂O

c) Write a symbol equation and an ionic equation for: Propanoic acid reacting with magnesium.

2CH₃CH₂COOH + Mg → (CH₃CH₂COO⁻)₂Mg²⁺ + H₂

2H⁺ + Mg → Mg²⁺ + H₂

d) Write a symbol equation and an ionic equation for: Methanoic acid reacting with sodium carbonate.

2HCOOH + Na₂CO₃ → 2HCOO⁻Na⁺ + H₂O + CO₂

2H⁺ + CO₃²⁻ → H₂O + CO₂

e) Write a symbol equation and an ionic equation for: Ethanoic acid reacting with copper oxide.

2CH₃COOH + CuO → (CH₃COO⁻)₂Cu²⁺ + H₂O

2H⁺ + CuO → Cu²⁺ + H₂O

3. Acidity & Properties

5. Propanoic acid, ethanoic acid and chloroethanoic acid are all weak acids.
a) State which is a stronger acid: propanoic acid or ethanoic acid. Explain why.

Ethanoic acid is stronger.

Alkyl groups are electron pushing (positive inductive effect). This pushes charge towards the acid group, making the COO⁻ ion more negative and less stable. This shifts the equilibrium to the left, resulting in a weaker acid. Propanoic acid has a larger alkyl group, so the effect is stronger.

b) State which is a stronger acid: chloroethanoic acid or ethanoic acid. Explain why.

Chloroethanoic acid is stronger.

Chlorine is electronegative and electron withdrawing (negative inductive effect). This pulls charge away from the acid group, stabilising the COO⁻ ion. This shifts the equilibrium of dissociation to the right.

6. Carboxylic acids can be formed from alcohols and carbonyls. For each of the following, state whether they can or cannot be used to make carboxylic acids.
a) CH₃CHOHCH₃

No (Oxidises to a Ketone).

b) CH₃CH₂CH₂OH

Yes (Oxidises to Carboxylic Acid).

c) CH₃CHOCH₃

No.

d) CH₃CH₂CHO

Yes (Oxidises to Carboxylic Acid).

e) CH₃C(CH₃)(OH)CH₃

No (Cannot be oxidised).

f) Write the equation for the production of methanoic acid from methanol.

CH₃OH + 2[O] → HCOOH + H₂O

7. Compare the boiling points of ethanol, ethanal, and ethanoic acid. State the order of their boiling points and explain the trend.

Lowest: Ethanal < Ethanol < Ethanoic Acid :Highest

Ethanal: Lowest boiling point. It has permanent dipole-dipole interactions but cannot hydrogen bond with itself.

Ethanol: Higher boiling point. It can form hydrogen bonds (one per molecule) due to the -OH group.

Ethanoic Acid: Highest boiling point. It can form more hydrogen bonds (dimers) than ethanol because it has both a C=O and an -OH group, leading to stronger intermolecular forces.

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