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(This section is in Chp 18 pages 605 – 612)

Determining Strengths of Acids and Bases. (This section is in Chp 18 pages 605 – 612). -. +. Strength. Strong Acids – Dissociate almost completely in water to produce H 3 O + ions Strong Bases – Strongly attract hydrogen ions in water, thus leaving OH -. STRONG ACIDS "The Big Six”.

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(This section is in Chp 18 pages 605 – 612)

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  1. Determining Strengths of Acids and Bases (This section is in Chp 18 pages 605 – 612)

  2. - + Strength • Strong Acids – Dissociate almost completely in water to produce H3O+ ions • Strong Bases – Strongly attract hydrogen ions in water, thus leaving OH- STRONG ACIDS "The Big Six” STRONG BASES HBr HI HClO4 HCl HNO3 H2SO4 Ca(OH)2 CaO NaOH KOH

  3. - + Strength • Weak Acids – Dissociate slightly in water to produce H3O+ ions. Do not readily dissociate. • Weak Bases – react only partially with water to form OH- ions. WEAK BASES WEAK ACIDS HF HC2H3O2 H3PO4 CO32- PO43- NH3 H2NNH2 H2CO3 HCN

  4. HC2H3O2 + H2O HC2H3O2 + H2O H3O++ C2H3O2– H3O++ C2H3O2– SINGLE ARROW Strong Acid: HCl + H2O  H3O+ + Cl– DOUBLE ARROW Weak Acid:

  5. SINGLE ARROW Strong Base: CaO Ca2+ + O2– O2–+ H2O 2OH– DOUBLE ARROW Weak Base: CO32-+ H2O HCO3- + OH–

  6. Strong & Weak

  7. Acid Dissociation Constant Ka is a measure of the strength of an acid. HA(aq)+ H2O (l) H3O+ (aq)+ A– (aq) The greater the Ka, the stronger the acid! Ka = [H3O+][A-] [HA]

  8. If the acid is diprotic or triprotic, the loss of each hydrogen is a separate ionization. Each ionization results in a different Ka value.

  9. Base Dissociation Constant Kb is a measure of the strength of a base. B(aq)+ H2O(l) HB(aq)+ OH– (aq) The greater the Kb, the stronger the base! Kb = [HB][OH-] [B]

  10. Practice Problem #1 Acetic acid is a weak monoprotic acid. If the initial concentration of acetic acid is 0.200 M and the equilibrium concentration of H3O+ is 0.0019 M, calculate Ka for acetic acid. HA(aq)+ H2O(l) H3O+ (aq)+ A– (aq) [H3O+][A-] Ka = [HA]

  11. Practice Problem #1 HA(aq)+ H2O(l) H3O+ (aq)+ A– (aq) [H3O+][A-] Ka = [H3O+] = [A-] [HA] Use Stoichiometry! The reaction produces an A- ion for every H3O+ ion.

  12. Practice Problem #1 HA(aq)+ H2O(l) H3O+ (aq)+ A– (aq) The equilibrium concentration of HA equals its initial concentration minus the amount that ionizes. [H3O+][A-] Ka = [HA] [HA] = 0.200M – 0.0019M [HA] = 0.1981M

  13. Practice Problem #1 HA(aq)+ H2O(l) H3O+ (aq)+ A– (aq) [H3O+][A-] (0.0019M)(0.0019M) Ka = = [HA] (0.1981M) [H3O+] = [A-] = 0.0019M = 1.8 x 10-5 [HA] = 0.1981M

  14. Acid-Base Properties of Salts Salts dissociate in water to form H3O+ or OH- Knowing what type of acid and base formed the salt helps predict salt solution acid-base properties.

  15. Acid-Base Properties of Salts RULES: Strong Acid + Strong Base Neutral Salt Strong Acid + Weak Base Acidic Salt Weak Acid + Strong Base Basic Salt Weak Acid + Weak Base Cannot predict very easily

  16. Neutral Salt HCl + NaOH NaCl STRONG ACID & BASE

  17. Acidic Salt NH3 + HCl NH4Cl WEAK BASE STRONG ACID

  18. Basic Salt NaOH + H2CO3 Na2CO3 STRONG BASE WEAK ACID

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