Carboxylic Acids
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Carboxylic Acids — Free MYP5 Chemistry Practice Questions

1QuestionFunctional group (-COOH) / General FormulaConcept Practice
2 marks~3 minCriterion A
Propanoic acid has the following structural formula:

HHO∣∣∥H−C−C−C−O−H∣∣HH\begin{array}{ccccc}
H & H & O & & \\
| & | & \| & & \\
H-C & - & C-C-O-H & & \\
| & & | & & \\
H & & H & & \\
\end{array}
a
Identify the carboxyl functional group in the structure above by circling or labelling it clearly. [1]
b
Deduce the molecular formula of propanoic acid from its structural formula, and explain how the presence of the carboxyl group accounts for the acidic behaviour of carboxylic acids in aqueous solution. [1]
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Solutions

2QuestionReactions:With metals and With bases (neutralization) and With carbonates (CO₂ production)Assessment Practice
5 marks~8 minCriterion C
When 0.100.10 mol of each carboxylic acid reacts with excess sodium carbonate at room temperature and pressure, the following volumes of CO2CO_2 are collected.

Acidmethanoicethanoicpropanoicbutanoic
Molar mass (g/mol)46607488
Volume of CO2CO_2 (cm³)2400240024001200


At room temperature and pressure, 1 mol of gas occupies 24 000 cm³.
a
Construct the balanced chemical equation, with state symbols, for the reaction of ethanoic acid with sodium carbonate. [1]
b
Deduce the expected volume of CO2CO_2 produced when 0.10 mol of a monoprotic carboxylic acid reacts with excess sodium carbonate, and show your reasoning. [2]
c
Analyse the data to identify the anomalous result and evaluate whether the trend in acid strength across the homologous series can account for the anomaly. [2]
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Solutions

3QuestionNaming carboxylic acidsAssessment Practice
5 marks~8 minCriterion D
Methanoic acid (HCOOHHCOOH, 1 carbon) is found in ant venom and causes skin irritation. Butanoic acid (C3H7COOHC_3H_7COOH, 4 carbons) is responsible for the smell of rancid butter and can cause nausea. In the IUPAC naming system for carboxylic acids, the prefix indicates the number of carbon atoms in the chain: methanoic = 1C, ethanoic = 2C, propanoic = 3C, butanoic = 4C.
a
State the IUPAC name of the carboxylic acid with 5 carbon atoms in its chain. [1]
b
Explain how the chain length indicated by an IUPAC name can be used to predict the volatility and health effects of a carboxylic acid. Use methanoic acid and butanoic acid as examples. [2]
c
Evaluate the reliability of using an IUPAC name alone to assess the health risks of a carboxylic acid, identifying at least one specific limitation. [2]
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4QuestionFunctional group (-COOH) / General FormulaAssessment Practice
2 marks~3 minCriterion B
The molecular formulas of the first four carboxylic acids are given below.

Carboxylic acidMethanoicEthanoicPropanoicButanoic
Number of carbon atoms (nn)1234
Molecular formulaCH2O2CH_2O_2C2H4O2C_2H_4O_2C3H6O2C_3H_6O_2C4H8O2C_4H_8O_2
a
Deduce the general formula that relates the number of carbon atoms nn to the molecular formula of these carboxylic acids. [1]
b
Justify the prediction that pentanoic acid (n=5n = 5) has the molecular formula C5H10O2C_5H_{10}O_2, by referring to the structure of the carboxylic acid functional group −COOH-COOH. [1]

Solutions

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