Skip to main content
Chemistry LibreTexts

Sulfide Ion (S²⁻)

  • Page ID
    97285
  • \( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \) \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\) \(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)\(\newcommand{\AA}{\unicode[.8,0]{x212B}}\)

    Acid Equilibria

    Sulfide is a strong base, so solutions of sulfide in water are basic, due to hydrolysis. Sulfide solutions develop the characteristic rotten-egg odor of \(\ce{H2S}\) as a result of this hydrolysis.

    \[\ce{S2^{-}(aq) + H2O(l) <=> HS^{-}(aq) + OH^{-}(aq) } \nonumber \]

    with \(K_b = 8.3\) and

    \[\ce{H^{-}(aq) + H2O(l) <=> H2S(aq) + OH^{-}(aq)} \nonumber \]

    with \(K_b = 1 \times 10^{-7}\).

    Solubility

    Many sulfide salts are insoluble in acidic or basic solution:

    • Acidic: \(\ce{PbS}\), \(\ce{Bi2S3}\), \(\ce{CuS}\), \(\ce{CdS}\), \(\ce{HgS}\), \(\ce{As2S3}\), \(\ce{Sb2S3}\), \(\ce{SnS2}\)
    • Basic: \(\ce{CoS}\), \(\ce{FeS}\), \(\ce{MnS}\), \(\ce{NiS}\), \(\ce{ZnS}\)

    Those salts that are insoluble in acidic solution are also insoluble in basic solution.

    A common test for aqueous sulfide ion involves acidification to form \(\ce{H2S}\), then exposure to moistened lead acetate paper to form black \(\ce{PbS}\) on the paper:

    \[\ce{Pb(OAc)2 + H2S -> PbS + 2HOAc} \nonumber \]

    Oxidation-Reduction:

    \(\ce{S2^{-}}\) or \(\ce{H2S}\) can be oxidized to yellow elemental sulfur in a colloidal form with fairly mild oxidizing agents, including nitric acid.


    This page titled Sulfide Ion (S²⁻) is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by James P. Birk.

    • Was this article helpful?