.. DO NOT EDIT.
.. THIS FILE WAS AUTOMATICALLY GENERATED BY SPHINX-GALLERY.
.. TO MAKE CHANGES, EDIT THE SOURCE PYTHON FILE:
.. "api/gallery/solutions/acid_base/plot_08_bronsted_lowry_conjugate_pairs.py"
.. LINE NUMBERS ARE GIVEN BELOW.

.. only:: html

    .. note::
        :class: sphx-glr-download-link-note

        :ref:`Go to the end <sphx_glr_download_api_gallery_solutions_acid_base_plot_08_bronsted_lowry_conjugate_pairs.py>`
        to download the full example code.

.. rst-class:: sphx-glr-example-title

.. _sphx_glr_api_gallery_solutions_acid_base_plot_08_bronsted_lowry_conjugate_pairs.py:


Bronsted-Lowry conjugate acid-base pairs: pKa + pKb = pKw
===========================================================

In the Bronsted-Lowry picture an acid is a proton donor and its
deprotonated form is a *conjugate base* -- itself a genuine base that
accepts a proton from water. For every pair, :math:`K_aK_b = K_w`, so the
stronger the acid, the weaker its conjugate base. Here the acetate ion is
modelled as a base in its own right with
:class:`~chemistrykit.solutions.systems.acid_base.WeakBase`
(:math:`K_b = K_w/K_a`), alongside acetic acid as
:class:`~chemistrykit.solutions.systems.acid_base.WeakAcid`, and several
conjugate pairs are placed on the line :math:`pK_a + pK_b = 14`.

.. GENERATED FROM PYTHON SOURCE LINES 17-61

.. code-block:: Python

    import matplotlib.pyplot as plt
    import numpy as np

    from chemistrykit.solutions.systems.acid_base import WeakAcid, WeakBase

    Kw = 1.0e-14
    pairs = {
        "HF / F$^-$": 6.8e-4,
        "CH$_3$COOH / CH$_3$COO$^-$": 1.8e-5,
        "H$_2$CO$_3$ / HCO$_3^-$": 4.5e-7,
        "NH$_4^+$ / NH$_3$": 5.6e-10,
        "HCN / CN$^-$": 6.2e-10,
    }

    fig, (ax1, ax2) = plt.subplots(1, 2, figsize=(12, 5))
    pKa_line = np.linspace(0, 14, 2)
    ax1.plot(pKa_line, 14 - pKa_line, color="gray", linestyle="--", label="pKa + pKb = 14")
    for name, Ka in pairs.items():
        pKa, pKb = -np.log10(Ka), -np.log10(Kw / Ka)
        ax1.plot(pKa, pKb, "o")
        ax1.annotate(name, (pKa, pKb), textcoords="offset points", xytext=(6, 2), fontsize=8)
    ax1.set_xlabel("pKa of the acid")
    ax1.set_ylabel("pKb of its conjugate base")
    ax1.set_title("Conjugate pairs: stronger acid, weaker base")
    ax1.legend()

    # 0.10 M solutions of each acid and of its conjugate base (e.g. as the
    # sodium salt): the acid solution is acidic, the conjugate-base solution
    # is basic, and both are computed with the same exact cubic.

    names = list(pairs)
    pH_acid = [WeakAcid(Ca=0.10, Ka=Ka).pH() for Ka in pairs.values()]
    pH_base = [WeakBase(Cb=0.10, Kb=Kw / Ka).pH() for Ka in pairs.values()]
    x = np.arange(len(names))
    ax2.bar(x - 0.2, pH_acid, width=0.4, color="indianred", label="0.10 M acid")
    ax2.bar(x + 0.2, pH_base, width=0.4, color="steelblue", label="0.10 M conjugate base")
    ax2.axhline(7.0, color="gray", linestyle=":")
    ax2.set_xticks(x)
    ax2.set_xticklabels(names, rotation=25, ha="right", fontsize=8)
    ax2.set_ylabel("pH")
    ax2.set_title("pH of each member of the pair")
    ax2.legend(fontsize=8)
    fig.tight_layout()




.. image-sg:: /api/gallery/solutions/acid_base/images/sphx_glr_plot_08_bronsted_lowry_conjugate_pairs_001.png
   :alt: Conjugate pairs: stronger acid, weaker base, pH of each member of the pair
   :srcset: /api/gallery/solutions/acid_base/images/sphx_glr_plot_08_bronsted_lowry_conjugate_pairs_001.png
   :class: sphx-glr-single-img





.. GENERATED FROM PYTHON SOURCE LINES 62-63

Acetate as a Bronsted base in its own right:

.. GENERATED FROM PYTHON SOURCE LINES 63-68

.. code-block:: Python


    acetate = WeakBase(Cb=0.10, Kb=Kw / 1.8e-5)
    print(f"0.10 M sodium acetate: Kb = {acetate.Kb:.3e}, pH = {acetate.pH():.3f}")

    plt.show()




.. rst-class:: sphx-glr-script-out

 .. code-block:: none

    0.10 M sodium acetate: Kb = 5.556e-10, pH = 8.872





.. rst-class:: sphx-glr-timing

   **Total running time of the script:** (0 minutes 0.077 seconds)


.. _sphx_glr_download_api_gallery_solutions_acid_base_plot_08_bronsted_lowry_conjugate_pairs.py:

.. only:: html

  .. container:: sphx-glr-footer sphx-glr-footer-example

    .. container:: sphx-glr-download sphx-glr-download-jupyter

      :download:`Download Jupyter notebook: plot_08_bronsted_lowry_conjugate_pairs.ipynb <plot_08_bronsted_lowry_conjugate_pairs.ipynb>`

    .. container:: sphx-glr-download sphx-glr-download-python

      :download:`Download Python source code: plot_08_bronsted_lowry_conjugate_pairs.py <plot_08_bronsted_lowry_conjugate_pairs.py>`

    .. container:: sphx-glr-download sphx-glr-download-zip

      :download:`Download zipped: plot_08_bronsted_lowry_conjugate_pairs.zip <plot_08_bronsted_lowry_conjugate_pairs.zip>`


.. only:: html

 .. rst-class:: sphx-glr-signature

    `Gallery generated by Sphinx-Gallery <https://sphinx-gallery.github.io>`_