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Acids and Bases

Acids and Bases. Electrolytes. Substance that conducts electricity when dissolved in water Ionizes in water Examples: aqueous ionic solutions, acids, bases. Properties of Acids. Acids have a pH less than 7.0 Acids will burn your skin Dilute acids have a sour taste

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Acids and Bases

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  1. Acids and Bases

  2. Electrolytes • Substance that conducts electricity when dissolved in water • Ionizes in water Examples: aqueous ionic solutions, acids, bases

  3. Properties of Acids • Acids have a pH less than 7.0 • Acids will burn your skin • Dilute acids have a sour taste • Strong acids are good conductors of electricity • Acids react with bases to form water and a salt (neutralization reaction) • Acids react with certain metals to produce hydrogen gas • Metals above H2 will react with acids to produce H2(g)

  4. Properties of Bases • Bases have a pH greater than 7.0 • Bases have a slippery or soapy feeling • Dilute bases have a bitter taste • Strong bases are good conductors of electricity • Bases react with acids to form water and a salt (neutralization reaction)

  5. Common Acids and Bases

  6. pH Scale • Scale ranges from 0-14 • Acids = pH less than 7 • Bases = pH greater than 7 • Neutral = pH = 7

  7. pH of common substances

  8. Indicators • Common indicators are listed in Table M Examples: • What color will thymol blue be in a solution with a pH of 6.5? • What color will methyl orange turn if a solution has a pH of 7.0? • What color will phenolphthalein turn in an acid?

  9. Arrhenius Theory • Definition of acids and bases • Acids – substances whose water solution contain hydrogen ions (H+), ionize to produce H+ • Bases – substances whose water solutions contain hydroxide ions (OH-), ionize to produce OH- • Properties of acids and bases are due to an excess of H+ or OH- ions

  10. Hydrogen/Hydronium • H+ cannot exist unbonded in a system; instead it is bonded with a water molecule to make the hydronium ion (H3O+) • H+ and (H3O+) are both used to indicate the presence of an acid

  11. Bronsted-Lowry Theory • Acids – donate/lose H+ • Bases – gain H+ Example: NH3 + H2O  NH4+ + OH- • H2O is the • NH3 is the

  12. Strength of Acids/Bases • Strength is proportional to the degree to which it ionizes in solution • Greater dissociation (more ions), stronger

  13. Ionization Constant for Water Kw • For pure water, at 25oC • Kw = 1.0 x 10-14 = [H+][OH-] • Kw is a constant • therefore [H+][OH-] = 1.0 x 10-14 • Examples: 1. Find the [OH-] concentration if [H+] = 10-8 2. Find the [H+] concentration if [OH-] = 10-3 3. Find the [OH-] concentration if [H+] = 10-7 * Exponents add up to -14

  14. Hydrogen Ion Concentration (pH) • used for convenience • pH = -log [H+] • Examples: • [H+] = 1.0 x 10-7, pH = • 2. [H+] = 1.0 x 10-3.5, pH = • Acids: pH is lower than 7, [H+] is greater than [OH-] • Bases: pH is greater than 7, [H+] is less than [OH-]

  15. Hydroxide Ion Concentration (pOH) • pOH = -log [OH-] • Since [H+][OH-] = 1.0 x 10-14 • pH + pOH = 14 • Examples: • Find the pOH of a solution with a pH = 8. Is this solution acidic or basic? • Find the pH of a solution with a pOH = 12. Is this solution acidic or basic?

  16. Concentration and pH • A change of 1 in pH is a tenfold increase in acid or base strength • A pH of 4 is 10 times more acidic than a pH of 5 • A pH of 12 is 100 times more basic than a pH of 10

  17. Mono/Di/Triprotic • Monoprotic acids • produce a single hydrogen ion • Examples: HCl, HBr • Diprotic aicds • produce two hydrogen ions • Examples: H2SO4, H2S • Triprotic acids • produce three hydrogen ions • Examples: H3PO4

  18. Neutralization Reactions • An acid and a base react together to form water and an ionic salt Examples: • HCl + NaOH  H2O + NaCl • H2SO4 + Ca(OH)2 2H2O + CaSO4 • HNO3 + Ca(OH)2

  19. Acid-Base Titrations • Process of adding a measured volume of an acid (or a base) of known molarity to a base (or an acid) of unknown molarity until neutralization occurs • Standard Solution – acid or base of known molarity • End Point – point of neutralization • Unknown molarity is calculated using the titration formula

  20. Titration • MAVA = MBVB equation • MA = Molarity of H+ • MB = Molarity of OH- • Moles of acid = moles of base (moles = molarity x liters)

  21. Titration Examples • What volume of 1.0M sulfuric acid can be neutralized by 50.0mL of 3.0M sodium hydroxide? • 50.0mL of a 0.250M KOH are needed to neutralize 20.0mL of a HCl solution of unknown concentration. What is the concentration of the HCl?

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