What is the carboxyl functional group?

The carboxyl functional group is -COOH.


The carboxyl group, which consists of a carbonyl (C=O) group and a hydroxyl (-OH) group, is present in carboxylic acids.

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What suffix is used to name carboxylic acids?

Carboxylic acids are named using the suffix -oic acid.


The carboxylic acid carbon is counted as part of the carbon chain of the root, e.g., HCOOH is methanoic acid.

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Why are carboxylic acids soluble in water?

Carboxylic acids are soluble in water because their C=O and O-H bonds are polar which allows them to form hydrogen bonds with water molecules, as shown below.

Carboxylic acids become less soluble as their chain length increases; this is because their non-polar carbon chain has a greater effect on the overall polarity of the molecule.

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Explain whether carboxylic acids are strong acids or weak acids.

Carboxylic acids are weak acids because they only partially dissociate when dissolved in water.


For example, methanoic acid partially dissociates in water: HCOOH(aq) ⇌ H+(aq) + HCOO-(aq).

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Describe the reactions of carboxylic acids with metals.

Carboxylic acids react with metals in redox reactions to form hydrogen gas and a carboxylate salt. The metal visibly disappears as it is oxidised.


For example, methanoic acid reacts with magnesium to form magnesium methanoate, and hydrogen:

2HCOOH + Mg ➔ (HCOO)2Mg + H2.

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Describe the reactions of carboxylic acids with metal oxides

Carboxylic acids react with metal oxides in neutralisation reactions to form a carboxylate salt and water.


For example, methanoic acid reacts with calcium oxide to form calcium methanoate and water:

2HCOOH + CaO ➔ (HCOO)2Ca + H2O.

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Describe the reactions of carboxylic acids with metal carbonates.

Carboxylic acids react with metal carbonates in neutralisation reactions. A carboxylate salt, water, and carbon dioxide are formed.


For example, methanoic acid reacts with sodium carbonate to produce sodium methanoate, water, and carbon dioxide: 2HCOOH + Na2CO3 ➔ 2HCOONa + H2O + CO2.

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Describe the chemical test to identify the presence of a carboxyl group.

The test is a reaction with sodium carbonate (Na2CO3) or sodium hydrogencarbonate (NaHCO3). Carboxylic acids react with carbonates to produce carbon dioxide gas. No other common organic compounds react with carbonates.


For example, methanoic acid reacts with sodium carbonate to produce sodium methanoate, water, and carbon dioxide: 2HCOOH + Na2CO3 ➔ 2HCOONa + H2O + CO2.

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Outline 3 types of reaction that can be used to produce carboxylic acids.

  1. Oxidation of primary alcohols and aldehydes with acidified K2Cr2O7 under reflux.
  2. Hydrolysis of nitriles with dilute acid or alkali followed by acidification.
  3. Hydrolysis of esters with dilute acid or alkali and heat followed by acidification.


Carboxylic acids can also be produced by the hydrolysis of acyl chlorides. 

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