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Chapter 19 Notes, part IV

Chapter 19 Notes, part IV. Strong and Weak Acids/Bases. Strong/Weak Acids and Bases. Whether an acid or base is considered strong is based on how much they dissociate , or break down into ions, when in solutions. Strong/Weak Acids and Bases.

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Chapter 19 Notes, part IV

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  1. Chapter 19 Notes, part IV Strong and Weak Acids/Bases

  2. Strong/Weak Acids and Bases • Whether an acid or base is considered strong is based on how much they dissociate, or break down into ions, when in solutions.

  3. Strong/Weak Acids and Bases • A strong acid is completely ionized in aqueous solution. • A weak acid is only partly ionized in aqueous solution. • A strong base is completely ionized in aqueous solution. • A weak base is only partly ionized in aqueous solution.

  4. Strong/Weak Acids and Bases • Strong acids include: • Binary acids—HCl, HBr, HI • Ternary acids—HNO3, HClO3, HClO4, H2SO4 • Strong bases include: • All hydroxides with metals in the first two groups on the periodic table except Be and Mg.

  5. Dissociation Constants • The acid dissociation constant tells how much an acid will break into ions in water, giving us an index for strength of an acid. • For the reaction of an acid: • HA + H2O D H3O+ + A- • The formula is: • Ka = [H3O+][A-] [HA]

  6. Dissociation Constants • Acids that have more than one hydrogen ion (diprotic and triprotic acids) will have more than one Ka. For example, • H3PO4D H+ + H2PO4- Ka = 7.5x10-3 • H2PO4-D H+ + HPO42- Ka = 6.2x10-8 • HPO42-D H+ + PO43- Ka = 4.8x10-13

  7. Dissociation Constants • Kb works the same way, except it measures dissociation of bases. • For the equation: • XOH D X+ + OH- • The formula is: • Kb = [X+][OH-] [XOH]

  8. % Ionization • Another way in which dissociation can be written is as a percent ionization, which tells you what percentage of the hydrogen ions will dissociate.

  9. Practice Problem #1 • A 0.100M solution of acetic acid (HC2H3O2) is only partially ionized. From measurements of the pH of the solution, [H+] is 1.34x10-3M. What is Ka for acetic acid?

  10. Practice Problem #2 • A 0.0250M solutions of HNO2 has a pH of 3.50. What is the Ka for nitrous acid?

  11. Practice Problem #3 • What is the pH of a 0.315M HMnO4 solution if its Ka is 1.52x10-5?

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