Skip to main content
Chemistry LibreTexts

5.5: Chemical Properties of Carboxylic Acids- Ionization and Neutralization

  1. Last updated
  2. Save as PDF
  • Page ID
    338518

    • \( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \) \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\) \(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)\(\newcommand{\AA}{\unicode[.8,0]{x212B}}\)

    Learning Objectives

    • Name the typical reactions that take place with carboxylic acids.
    • Describe how carboxylic acids react with basic compounds.

    Water-soluble carboxylic acids ionize slightly in water to form moderately acidic solutions.

    \(\mathrm{RCOOH+H_2O\rightleftharpoons RCOO^-+H_3O^+}\)

    Their aqueous solutions exhibit the typical properties of acids, such as changing litmus from blue to red.

    The anion formed when a carboxylic acid dissociates is called the carboxylate anion (RCOO−).

    Whether soluble in water or not, carboxylic acids react with aqueous solutions of sodium hydroxide (NaOH) to form salts:

    RCOOH + NaOH(aq) → RCOO−Na+(aq) + H2O

    In these reactions, the carboxylic acids act like inorganic acids: they neutralize basic compounds. 

    Carboxylic acid salts are named in the same manner as inorganic salts: the name of the cation is followed by the name of the organic anion. The name of the anion is obtained by dropping the -ic ending of the acid name and replacing it with the suffix -ate. This rule applies whether we are using common names or International Union of Pure and Applied Chemistry (IUPAC) names:

    carboxylic acid salts.jpg

    The salts of long-chain carboxylic acids are called soaps. We discuss the chemistry of soaps elsewhere.

    soaps.jpg

    Example \(\PageIndex{1}\)

    Write an equation for each reaction.

    1. the ionization of propionic acid in water (H2O)
    2. the neutralization of propionic acid with aqueous sodium hydroxide (NaOH)

    Solution

    Propionic acid has three carbon atoms, so its formula is CH3CH2COOH.

    1. Propionic acid ionizes in water to form a propionate ion and a hydronium (H3O+) ion. CH3CH2COOH(aq) + H2O(ℓ) → CH3CH2COO−(aq) + H3O+(aq)
    2. Propionic acid reacts with NaOH(aq) to form sodium propionate and water. CH3CH2COOH(aq) + NaOH(aq) → CH3CH2COO−Na+(aq) + H2O(ℓ)

    Exercise \(\PageIndex{1}\)

    Write an equation for each reaction.

    1. the ionization of formic (methanoic acid) acid in water
    2. the ionization of p-chlorobenzoic acid in water

    Example \(\PageIndex{2}\)

    Write an equation for the reaction of decanoic acid with each compound.

    1. aqueous sodium hydoxide (NaOH)
    2. aqueous potassium hydroxide (KOH)

    Solution

    1. Decanoic acid has 10 carbon atoms. It reacts with NaOH to form a salt and water (H2O). CH3(CH2)8COOH + NaOH(aq) → CH3(CH2)8COO−Na+(aq) + H2O(ℓ)
    2. With KOH, the products are a salt and H2O.  CH3(CH2)8COOH + KOH(aq) → CH3(CH2)8COO−K+(aq) + H2O(ℓ) 

    Exercise \(\PageIndex{3}\)

    Write an equation for the reaction of benzoic acid with each compound.

    1. aqueous sodium hydroxide (NaOH)
    2. aqueous potassium hydroxide (KOH)

    To Your Health: Organic Salts as Preservatives

    Some organic salts are used as preservatives in food products. They prevent spoilage by inhibiting the growth of bacteria and fungi. Calcium and sodium propionate, for example, are added to processed cheese and bakery goods; sodium benzoate is added to cider, jellies, pickles, and syrups; and sodium sorbate and potassium sorbate are added to fruit juices, sauerkraut, soft drinks, and wine. Look for them on ingredient labels the next time you shop for groceries.

    organic salts.jpg

    Concept Review Exercises

    1. What products are formed when a carboxylic acid is neutralized with a strong base? What additional product is formed when a carboxylic acid is neutralized with a carbonate or a bicarbonate?

    Answers

    1. A carboxylate salt and water.

    Key Takeaways

    • Soluble carboxylic acids are weak acids in aqueous solutions.
    • Carboxylic acids neutralize bases to form salts.

    Exercises

    1. Write the equation for the ionization of CH3CH2CH2COOH in water.

    2. Write the equation for the neutralization of CH3CH2CH2COOH with sodium hydroxide [NaOH(aq)].

    3. Write the equation for the reaction of CH3COOH with potassium hydroxide [KOH(aq)].

    4. Write the equation for the reaction of CH3CH2COOH with sodium hydroxide [NaOH(aq)].

    5. Write the equation for the ionization of propanoic acid in water.

    6. Write the equation for the ionization of 4-chloropentanoic acid in water.

    7. Write an equation for the reaction of benzoic acid with each compound.

      1. aqueous NaOH
      2. aqueous KOH

    8. Write the condensed structural formula for each compound.

      1. potassium ethanoate
      2. lithium propanoate

    9. Name each compound (IUPAC).

      1. CH3CH2CH2COO−Li+
      2. CH3CH2CH2COO−NH4+

    Answers

    1. CH3CH2CH2COOH(aq) + H2O(ℓ) → CH3CH2CH2COO−(aq) + H3O+(aq)

    1. CH3COOH + KOH(aq) → 2CH3COO−K+(aq) + H2O(ℓ) 

     

    1. CH3CH2COOH(aq) + H2O(ℓ) → CH3CH2COO−(aq) + H3O+(aq)

    1.  

      1. Screen Shot 2021-01-18 at 12.48.13 PM.png
      2. Screen Shot 2021-01-18 at 12.52.33 PM.png

     

    9.  a. lithium butanoate               b.  ammonium butanoate

    5.5: Chemical Properties of Carboxylic Acids- Ionization and Neutralization is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by LibreTexts.