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Acids & Bases Hydrolysis

Acids & Bases Hydrolysis. Lesson 7. Hydrolysis. Hydrolysis of a salt is… The reaction between water and the cation or anion ( or both) that make up the salt in order to produce either an acidic or basic solution. Hydrolysis. Hydrolysis of a salt is…

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Acids & Bases Hydrolysis

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  1. Acids & BasesHydrolysis Lesson 7

  2. Hydrolysis Hydrolysis of a salt is… • The reaction between water and the cation or anion ( or both) that make up the salt in order to produce either an acidic or basic solution.

  3. Hydrolysis Hydrolysis of a salt is… • All salts are considered 100% ionized in water. • We will only consider the reactions between the ions and water. • Ignore any reactions between the ions themselves.

  4. Hydrolysis Not all ions will react with water. The ones that do not are called “spectator ions” Memorize these spectator ions!

  5. Spectator ions • NaOH • HCl

  6. Spectator Ions Spectator Cations: alkali metals (group 1 on periodic table) + alkaline earth metals ( group 2 on periodic table) • Column I and column II Spectator Anions: the first 5 anions found on the top right of the table ClO4, I, Br, Cl, NO3 memorize them! HSO4 is not a spectator because it is a weak acid.

  7. So what to do with salts now? • Determine ions that make them up • Discard any spectators • Remaining ions will act as acids if found on the left side of table (acids), or they will act as bases if found on right side of the table.

  8. NaCl

  9. NH4Cl

  10. NaF

  11. Fe(H20)6Cl3

  12. Al(H2O)5(OH)(NO3)2

  13. Amphiprotic Ions Acids or Bases?

  14. Amphiprotic Ions H3PO4Acid H2PO4-Amphiprotic HPO42-Amphiprotic PO43-Base Amphiprotic ionshave a Ka and a Kb. If the Ka > Kb, then the ion is an acid. If the Kb > Ka, then the ion is a base.

  15. Is H2PO4- acid or basic acid

  16. 1. Is H2PO4- an acid or base when in water? Write the predominate hydrolysis equation for this ion. Ka (H2PO4-) = 6.2 x 10-8 Kb (H2PO4-)=Kw Ka(H3PO4) =1 x 10-14 7.5 x 10-3 =1.3 x 10-12 Ka > Kb Acid H2PO4- + H2O ⇄HPO42- + H3O+

  17. Is HPO42- acid or basic basic

  18. 2. Is HPO42- an acid or base when in water? Write the hydrolysis equation for this ion. Ka (HPO42-) = 2.2 x 10-13 Kb (HPO42-)= Kw Ka(H2PO4-) =1 x 10-14 6.2 x 10-8 =1.6 x 10-7 Kb > Ka base HPO42- + H2O ⇄H2PO4- + OH-

  19. 3. Show by calculation if NH4F is an acid or base when in water. NH4F → NH4+ + F- acid base Neither is a spectator; neither will cross off! What will the salt solution be? Ka(NH4+) = 5.6 x 10-10 Kb (F-) = = Kw Ka(HF) = 1 x 10-14 3.5 x 10-4 =2.9 x 10-11 Ka > Kbacid

  20. TRY Show by calculation if NH4CH3COO is an acid or base when in water. NH4CH3COO → NH4+ + CH3COO- acid base Ka(NH4+) = 5.6 x 10-10 Kb (CH3COO-) = = Kw Ka(CH3COOH) = 1 x 10-14 1.8 x 10-5 =5.6 x 10-10 Ka = Kbneutral pH = 7.00

  21. Homework • Hebden 148 • #69 (top row), #70 (top row) • # 71, 72, 73.

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