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Aqueous Chemistry : Acids, Bases, and pH

Aqueous Chemistry : Acids, Bases, and pH. Dissociation of Water. H 3 O + = hydronium ion. OH – = hydroxide ion. Dissociation of Water. Dissociation constant:. Brønsted-Lowry Definition. An Acid can donate protons to another molecule. Brønsted-Lowry Definition.

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Aqueous Chemistry : Acids, Bases, and pH

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  1. Aqueous Chemistry:Acids, Bases, and pH

  2. Dissociation of Water H3O+ = hydronium ion OH– = hydroxide ion

  3. Dissociation of Water Dissociation constant:

  4. Brønsted-LowryDefinition An Acid can donate protons to another molecule

  5. Brønsted-LowryDefinition A Base can accept protons from another molecule

  6. Strong acids dissociate completely Example: Hydrochloric acid In 1 liter of pure water: Add 0.1 moles of HCl

  7. Strong acids dissociate completely Example: Hydrochloric acid Add 10-8 moles of HCl to 1 liter of water NO!!! In 1 liter of pure water:

  8. Weak acids partially dissociate Example: Acetic acid What is the pH of a 0.1 M acetic acid solution? Simplifications:

  9. Bases bind to protons Example: Hydroxide Add 0.1 moles sodium hydroxide to 1 liter of water

  10. Comparing pKa Values pKa = 4.5 pKa = 10.5 Overall K for the reaction is: Therefore:

  11. Summary • Water dissociates into hydronium ions and hydroxide ions. • The negative log of the hydronium ion concentration is pH, a measure of acidity. • The negative log of the hydroxide ion concentration is pOH. • pOH + pH = 14 for all aqueous solutions.

  12. Summary • Adding an acid to a solution always lowers the pH. • Strong acids release nearly all of their protons to form hydronium ions. • Weak acids release relatively few protons to water, although addition of a base can remove more protons. • Adding a base to a solution always raises the pH.

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