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7.13: Bases: Naming and Formulas

  • Page ID
    53727
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    Making soap requires a base, lye
    Figure \(\PageIndex{1}\) (Credit: Unknown Author; Source: http://commons.wikimedia.org/wiki/File:Zeepzieden.jpg(opens in new window); License: Public Domain)

    What different things are these workers doing to make soap?

    Soap making has a long history. Until recently, soap was made using animal fats and lye from wood ashes. The lye served as a base to break down the fats and help form the soap. Needless to say, unless the soap was washed to remove the lye, it was very harsh on the skin. Many families would make their own soap by boiling the lye and fat in a large kettle over an open fire—a long and hot task.

    Bases

    A base can be simply defined as an ionic compound that produces hydroxide ions when dissolved in water. One of the most commonly used bases is sodium hydroxide, illustrated below.

    Figure \(\PageIndex{2}\): (A) Sodium hydroxide, a base, is a solid that is typically produced as small white pellets. (B) The structure of sodium hydroxide is an extended three-dimensional network. The purple spheres are the sodium ions \(\left( \ce{Na^+} \right)\). The red and white spheres are oxygen and hydrogen atoms, respectively, which are bonded together to form hydroxide ions \(\left( \ce{OH^-} \right)\). (Credit: (A) Martin Walker (Wikimedia: Walkerma); (B) Ben Mills (Wikimedia: Benjah-bmm27); Source: (A) http://commons.wikimedia.org/wiki/File:SodiumHydroxide.jpg(opens in new window); (B) http://commons.wikimedia.org/wiki/File:Sodium-hydroxide-crystal-3D-vdW.png(opens in new window); License: Public Domain)

    Names and Formulas of Bases

    There is no special system for naming bases. Since they all contain the \(\ce{OH^-}\) anion, names of bases end in hydroxide. The cation is simply named first. Some examples of names and formulas for bases are shown in the table below.

    Names and Formulas of Bases
    Table \(\PageIndex{1}\)
    Formula Name
    \(\ce{NaOH}\) sodium hydroxide
    \(\ce{Ca(OH)_2}\) calcium hydroxide
    \(\ce{NH_4OH}\) ammonium hydroxide

    Notice that because bases are ionic compounds, the number of hydroxides in the formula does not affect the name. The compound must be neutral, so the charges of the ions are balanced just as for other ionic compounds. The sodium ion \(\left( \ce{Na^+} \right)\) requires one \(\ce{OH^-}\) ion to balance the charge, so the formula is \(\ce{NaOH}\). Calcium \(\left( \ce{Ca^{2+}} \right)\) requires two \(\ce{OH^-}\) ions to balance the charge, so the formula is \(\ce{Ca(OH)_2}\). Hydroxide ion is a polyatomic ion, and must be in parentheses when there is more than one in a formula.

    Summary

    • Bases are ionic compounds that produce hydroxide ions when dissolved in water.
    • The cation is named first followed by "hydroxide."

    Review

    1. What is a base?
    2. What is the charge on the hydroxide anion?
    3. Name the following bases:
      1. LiOH
      2. Mg(OH)2
      3. Fe(OH)3
    4. Write the formulas for the following bases:
      1. nickel (II) hydroxide
      2. aluminum hydroxide
      3. silver hydroxide

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