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Chapter 18 Acids, Bases, and Salts

Chapter 18 Acids, Bases, and Salts. Acids Sour - lemons Feel like water React vigorously with metal Solution will conduct Blue to red litmus test Use a base to neutralize. Bases Bitter taste –horseradish. Slimy touch Do not react with metals Solution will conduct

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Chapter 18 Acids, Bases, and Salts

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  1. Chapter 18 Acids, Bases, and Salts

  2. Acids • Sour - lemons • Feel like water • React vigorously with metal • Solution will conduct • Blue to red litmus test • Use a base to neutralize

  3. Bases • Bitter taste –horseradish. • Slimy touch • Do not react with metals • Solution will conduct • Red to blue litmus paper • Use an acid to neutralize

  4. Arrhenius Definition – Acids dissociate in water to produce H+ ions. A base dissociates to produce OH- ions. • Acids have to have an H in their formula and bases have to have an OH in their formula.

  5. Bronsted-Lowry Definition – An acid is any substance that donates an H+ ion (known as a proton). A base is anything that accepts an H+ ion. • ***This is a more general definition.*** • Something can be a Bronsted-Lowry base but not be an Arrhenius base. For example, NH3 is a Bronsted-Lowry base but doesn’t have an OH so is not an Arrhenius base.

  6. **Water can act as an acid or a base making it amphoteric.** (IE it can either gain or lose an H) See below for example of a base. • Hydronium ion – H+ + H2O  H3O+ • H3O+ is called a Hydronium ion. It forms when H+ ions released from an acid combine with water.

  7. Conjugate Acid-Base Pairs – If an acid donates a proton (H+) the proton is accepted to form the conjugate base. (Hint: The pair is always different by one H)

  8. For example • NH3 + H2O  NH4+ + OH- • NH3 is the base and NH4+ is the conjugate acid. H2O is the acid and OH- is the conjugate base.

  9. 18-2 Determining the Strengths of Acids and Bases • Strong and Weak Acids • A strong acid readily transfers their H+ ions. • A weak acid does not readily transfer its H+ ions. • One way to tell is that strong acids dissociate in only one direction. • Ex. HCl  H+ + Cl-

  10. Weak acids will dissociate with reversible arrows  because the reaction will go back and forth. • Ex. HCN  H+ + CN- • Strong bases completely dissociate to form OH- ions in water. Weak bases only react to partially form OH- ions in water.

  11. Again one way to tell is that strong bases dissociate in only one direction. • Ex. NaOH  Na+ + OH-

  12. Weak bases will dissociate with reversible arrows  because the reaction will go back and forth. • Ex. CaCO3 Ca+2 + CO3-2

  13. Strengths of Conjugate Acid-Base Pairs • There is an inverse relationship between the strength of conjugate acid-base pairs. The stronger the acid the weaker its conjugate base and the stronger the base the weaker its conjugate acid.

  14. In the reversible reactions for weak acid or bases in water, Keq can be determined as with any reversible reaction. For weak acids Keq is now called Ka (for acid) and Keq is now called Kb for weak bases. Ka is called the acid dissociation constant and Kb is called the base dissociation constant. The value of the Ka or Kb indicates the strength of the acid or base.

  15. 19-1 The self-ionization of Water and pH • Self-ionization – water acts as both an acid and a base in the same reaction. • H2O (l) + H2O (l)  H3O+ (aq) + OH- (aq) • Ex. In pure water at 25 degrees C, both H3O+ and OH- ions are found at concentrations of 1.0 x 10-7 M

  16. Kw = [H3O+][OH-]  is the ion product constant • = (1.0 x 10-7)(1.0x10-7) • = 1.0x10-14 • Kw tells you the concentration of pure water.

  17. If the concentration of H3O+ in blood is 4.0x10-8M Is blood acidic, basic or neutral? • [H3O+][OH-] =Kw • [H3O+][OH-] = 1.0 x 10-14 • (4.0 x 10-8)[OH-] = 1.0 x 10-14 • Solve for [OH-] • [OH-] = 1.0x10-14= 2.5x10-7M • 4.0x10-8 • **Since the concentration is greater than 1.0x10-7, it is a basic solution.**

  18. The pH scale • pH = -log[H3O+] • In one brand of vegetable juice, the concentration of H3O+ ions is 7.3x10-5M. What is the pH of the juice? • pH =-log[7.3x10-5] = 4.14

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