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Chapter 20

Chapter 20. Acids and Bases. Section 20.1. Properties of Acids : Tart or sour taste (lemon juice) Electrolytic Both strong and weak Will cause indicators to change colors A metal + an acid will produce hydrogen gas Single replacement reaction Acid + Base → water + a “salt”

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Chapter 20

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  1. Chapter 20 Acids and Bases

  2. Section 20.1 • Properties of Acids: • Tart or sour taste (lemon juice) • Electrolytic • Both strong and weak • Will cause indicators to change colors • A metal + an acid will produce hydrogen gas • Single replacement reaction • Acid + Base → water + a “salt” • Double replacement reaction • Acids: • Something that produces a hydrogen ion (H+) in solution

  3. Properties of Bases: • Bitter • Slippery (soap) • Electrolytic • Both strong and weak • Will cause an indicator to change colors • Base: • Something that produces a hydroxide ion (OH1-) in solution

  4. Naming • HBr • Hydrogen with a single anion • Use prefix hydro- and suffix –ic • Hydrobromic acid • H2SO3 • Hydrogen with a polyatomic that ends in –ite • Change suffix to –ous • Sulfurous acid • HNO3 • Hydrogen with a polyatomic that ends in –ate • Change suffix to –ic • Nitric acid • Remember… “-ic, I -ate something gross!” • Know rules! (page 578, Table 20.1!!!)

  5. Section 20.2 • Self-ionization of water: • Reaction in which 2 water molecules produce ions • H2O + H2O → OH- + H3O+ • Also written as: • H2O ↔ H+ + OH- • The H3O+ and H+ represent hydrogen ions in solution.

  6. Neutral Solutions • In pure water, the concentration of hydrogen ions is equal to the concentration of hydroxide ions • 1 x 10-7M • [H+] = [OH-] • (brackets represent concentration) • This represents a neutral solution.

  7. Solutions • In a solution, if the [H+] increases, the [OH-] decreases and vice versa. • Ion-product constant of water, Kw: • Kw = [H+] x [OH-] = 1 x 10-14M • Acidic Solution: • The [H+] is greater than [OH-]. • Therefore, the [H+] is greater than 1 x 10-7M. • Basic Solution: • The is [H+] less than [OH-]. • Therefore, the [H+] is less than 1 x 10-7M. • A.k.a. alkaline solutions

  8. Problem • If the [H+] is 1 x 10-5M, is the solution acidic, basic, or neutral? What is the [OH-]?

  9. pH Scale • The pH scale ranges from 0-14. • 0 = strongly acidic • 7 = neutral • 14 = strongly basic • pH = -log [H+] • What is the pH of a neutral solution?

  10. Sample Problems • What is the pH of the following concentrations? • [H+] = 1 x 10-2M • [H+] = 1 x 10-9M • [H+] = 1 x 10-5M • As long as you have a 1 x 10 to some power, the pH is the exponent.

  11. Other Formulas and Problems • pOH = -log [OH-] • pH + pOH = 14 • What is the pH of a solution with a [OH-] of 4.0 x 10-11M? • Two ways to solve: • 1. find pOH then subtract from 14 Or • 2. Use Kw to find [H+] then find pH using –log function.

  12. Flow Chart of pH and pOH • Use the map to help you get from any point A to any point B… pH = -log [H+]pH + pOH = 14pOH = -log [OH-] [H+] ↔pH ↔ pOH ↔ [OH-] Kw = [H+] [OH-] = 1 x 10-14M

  13. More Samples • What is the [H+] of a solution with a pH of 3.7? • If the [H+] is 3.1 x 10-5M, what is the pH? What is the pOH? What is the [OH-]?

  14. Section 20.3 – Other definitions of Acids and Bases • Arrhenius Acids and Bases: • Acid: • Hydrogen containing compound that ionize to yield a hydrogen ion in solution. • Base: • Compounds that ionize to yield a hydroxide ion in solution.

  15. Brønsted – Lowry Acids and Bases • He felt the Arrhenius definition was too limiting. • Acids: • Hydrogen ion donor • Bases: • Hydrogen ion acceptor • Examples: • NH3 + H2O ↔ NH4+ + OH- • HCl + H2O ↔ H3O + + Cl-

  16. Conjugate Acids: • Particle formed when a base gains a hydrogen ion. • Conjugate Base: • Particle that remains when an acid has donated a hydrogen ion. • Example: • NH3 + H2O ↔ NH4+ + OH- • B A CA CB • HCl + H2O ↔ H3O + + Cl- • A B CA CB • Amphoteric: • Substance that can act as both an acid or a base.

  17. Strong Acids and Bases • Strong Acids/Bases: • Those that ionize completely in solution. • Ex: HCl, NaOH • Weak Acids/Bases: • Those that only slightly ionize in solution. • Ex: NH3, Acetic Acid (vinegar) • Tooth decay is caused by the weak acid – lactic acid: C3H6O3

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