If you like us, please share us on social media.
The latest UCD Hyperlibrary newsletter is now complete, check it out.

ChemWiki: The Dynamic Chemistry E-textbook > Development Details > Approaches > Demos > Additional Demos > Strengths of Acids

Copyright (c) 2006-2014 MindTouch Inc.

This file and accompanying files are licensed under the MindTouch Master Subscription Agreement (MSA).

At any time, you shall not, directly or indirectly: (i) sublicense, resell, rent, lease, distribute, market, commercialize or otherwise transfer rights or usage to: (a) the Software, (b) any modified version or derivative work of the Software created by you or for you, or (c) MindTouch Open Source (which includes all non-supported versions of MindTouch-developed software), for any purpose including timesharing or service bureau purposes; (ii) remove or alter any copyright, trademark or proprietary notice in the Software; (iii) transfer, use or export the Software in violation of any applicable laws or regulations of any government or governmental agency; (iv) use or run on any of your hardware, or have deployed for use, any production version of MindTouch Open Source; (v) use any of the Support Services, Error corrections, Updates or Upgrades, for the MindTouch Open Source software or for any Server for which Support Services are not then purchased as provided hereunder; or (vi) reverse engineer, decompile or modify any encrypted or encoded portion of the Software.

A complete copy of the MSA is available at http://www.mindtouch.com/msa

Strengths of Acids

Chemical Concepts Demonstrated

  • Relative strengths of acids
  • Properties and principles of acidity

Demonstration and Explanations

1. Compare HCl with H2S:  HCl is a stronger acid than H2S. Acids become stronger as the X-H bond becomes more polar.  The larger the difference in the electronegativity between X and H atoms, the easier it is to form H + and X - ions.

2. Compare H2S with distilled water: H2S is a stronger acid than water. Although the H-S bond is not as polar as the H-O bond, H2S is a stronger acid because of the size of the sulfur atom compared to that of oxygen.  The bond dissociation energy associated with larger atoms is greater than that of a smaller atoms because, given equal charges, the charge density is greater on the smaller atoms.  Lesser charge densities provide lower bond dissociation energies (i.e. weaker bonds).  Because the bond between H-S is weaker than H-O,  H2S will dissociate and form ions more easily than water and is therefore a stronger acid.

3. Compare H3PO4, NaH2PO4, Na2HPO4, and Na3PO4:  With respect to acidity, H3PO4 > NaH2PO4 > Na2HPO4 > Na3PO4.  According to the Bronsted definition of acids and bases, acids donate protons and bases accept them.  Proton donation becomes much more difficult as the resulting anions become more electronegative.  H3PO4 can form H2PO4more easily than H2PO4- can form HPO42-, etc.

4. Compare HClO and HClO4:  HClO4 is a stronger acid than HClO.   As the oxidation state of the central atom becomes larger, the acidity of the molecule increases. An atom becomes more electronegative as the oxidation number increases.  In this case, the chlorine atom draws electrons from the oxygen atoms that surround it.  This then causes the oxygen atoms to become more electronegative.  The O-H bond then becomes more polar and therefore more acidic.


Last modified
10:29, 2 Oct 2013



(not set)
(not set)

Creative Commons License Unless otherwise noted, content in the UC Davis ChemWiki is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License. Permissions beyond the scope of this license may be available at copyright@ucdavis.edu. Questions and concerns can be directed toward Prof. Delmar Larsen (dlarsen@ucdavis.edu), Founder and Director. Terms of Use