Photo AI
8. (a) (i) Explain, with the aid of a diagram, the acidic nature of the carboxylic acid functional group - Leaving Cert Chemistry - Question 8 - 2022
Question 8
8. (a) (i) Explain, with the aid of a diagram, the acidic nature of the carboxylic acid functional group. (ii) Give an example of a reaction that demonstrates the a... show full transcript
Worked Solution & Example Answer:8. (a) (i) Explain, with the aid of a diagram, the acidic nature of the carboxylic acid functional group - Leaving Cert Chemistry - Question 8 - 2022
Step 1
Explain, with the aid of a diagram, the acidic nature of the carboxylic acid functional group.
Answer
The carboxylic acid functional group, -COOH, exhibits acidic properties due to the ability of the hydrogen atom to dissociate as a proton (H+).
In aqueous solution, the carboxylic acid dissociates:
The resulting carboxylate ion (RCOO-) is stabilized by resonance structures, where the negative charge is delocalized between the two oxygen atoms. The inductive effect also plays a role; electronegative atoms or groups adjacent to the carboxyl group can attract electron density, enhancing the acidity.
Diagrammatically, the proton leaving the carboxylic acid is depicted alongside resonance structures:
O
||
R-C-OH ⇌ R-C=O
| / \\
O⁻ H⁺
This shows how the acidic nature is determined by both the resonance stabilization of the conjugate base and the inductive effects exerted by neighboring groups.
Step 2
Give an example of a reaction that demonstrates the acidic nature of ethanol.
Answer
A clear example of the acidic nature of ethanol is its reaction with sodium metal (Na):
In this reaction, ethanol donates a proton to sodium, forming sodium ethoxide and hydrogen gas, which demonstrates its behavior as a weak acid.
Step 3
Would you expect to observe a reaction when a drop of pure ethanol is added to solid sodium carbonate on a clock glass? Explain.
Answer
No, a reaction is not expected between pure ethanol and solid sodium carbonate (Na2CO3). Ethanol is a weak acid and does not have sufficient acidity to react with sodium carbonate, which is a weak base. Instead, sodium carbonate would remain largely unreactive in this context, as it is used primarily to react with stronger acids like hydrochloric acid.
Step 4
Step 5
Step 6
How many carbon atoms in a molecule of the ester E are in planar geometry?
Answer
In the molecule of ethyl methanoate, there are 3 carbon atoms. Out of these, the carbonyl carbon (C=O) and the adjacent two carbon atoms are in planar geometry, which applies to 3 carbon atoms in this structure.
Step 7
Classify this esterification reaction as a redox reaction, an acid-base reaction or a substitution reaction.
Answer
The esterification reaction between methanoic acid and ethanol is classified as a substitution reaction. In this process, the hydroxyl (-OH) group from the acid is replaced by the alkoxy (-O-alkyl) group from the alcohol.
Step 8
Step 9
Step 10
Explain why the boiling point of ethanoic acid (118 °C) is significantly higher than that of methyl methanoate (32 °C) although the two compounds have the same molecular formula C2H4O2.
Answer
The boiling point of ethanoic acid is significantly higher due to hydrogen bonding interactions present in its molecular structure. Ethanoic acid can form strong hydrogen bonds between molecules because of the presence of the -COOH group. In contrast, methyl methanoate, while it can form weaker interactions, lacks the capability for hydrogen bonding like ethanoic acid. Hence, the absence of strong intermolecular forces in methyl methanoate contributes to its much lower boiling point.