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ACIDS, BASES, AND pH

ACIDS, BASES, AND pH. Aqueous Solutions. How do we know ions are present?. The solutions conduct electricity! They are called ELECTROLYTES HCl, MgCl 2 , and NaCl are strong electrolytes . They dissociate completely (or nearly so) into ions. Aqueous Solutions. weak electrolyte,

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ACIDS, BASES, AND pH

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  1. ACIDS, BASES, AND pH

  2. Aqueous Solutions How do we know ions are present? The solutions conduct electricity! They are called ELECTROLYTES HCl, MgCl2, and NaCl are strong electrolytes. They dissociate completely (or nearly so) into ions.

  3. Aqueous Solutions weak electrolyte, like Acetic acid, ionizes only to a small extent, CH3CO2H(aq) t CH3CO2-(aq) + H+(aq)

  4. Aqueous Solutions Some compounds dissolve in water but do not conduct electricity. They are called nonelectrolytes. Examples include: sugar ethanol ethylene glycol

  5. Acid Properties • Sour taste (grape fruit) • Found in many fruits • Vinegar • Will burn if not diluted • Made up of Nonmetals • Acid formulas usually start with hydrogen- ex HCl, H2SO4

  6. Base Properties • Bitter taste • Slippery feel • Most household cleaners • Also dangerous if not diluted • Made up of a metal and nonmetals in formulas • Arrhenius bases start with metals in their formulas and end with a OH- ex NaOH, KOH, Ba(OH)2

  7. Arrhenius Theory • Substances ionize in water • Acids, bases, and salts when dissolved in water, will conduct electricity. • Called Electrolytes

  8. Arrhenius Theory • Acids release hydrogen ions (H+) • HCl → H+ + Cl- • Bases release hydroxide ions (OH-) NaOH → Na+ + OH-

  9. Strong and Weak Acids/Bases • Generally divide acids and bases into STRONG or WEAK ones. STRONG ACID: HNO3(aq) + H2O(liq) ---> H3O+(aq) + NO3-(aq) HNO3 is about 100% dissociated in water.

  10. Strong and Weak Acids/Bases HNO3, HCl, H2SO4 and HClO4 are among the only known strong acids.

  11. Strong Acids will completely ionize

  12. Strong and Weak Acids/Bases • Weak acids are much less than 100% ionized in water. One of the best known is acetic acid = CH3CO2H

  13. CaO Strong and Weak Acids/Bases • Strong Base: 100% dissociated in water. NaOH(aq) ---> Na+(aq) + OH-(aq) Other common strong bases include KOH and Ca(OH)2. CaO (lime) + H2O --> Ca(OH)2 (slaked lime)

  14. Strong and Weak Acids/Bases • Weak base: less than 100% ionized in water One of the best known weak bases is ammonia NH3(aq) + H2O(liq) e NH4+(aq) + OH-(aq)

  15. ACID-BASE THEORIES • The most general theory for common aqueous acids and bases is the BRØNSTED - LOWRY theory • ACIDS DONATE H+ IONS • BASES ACCEPT H+ IONS

  16. Bronsted Base: adds one hydrogen ion Reactants Products Bronsted Acid: removes one hydrogen ion

  17. ACID-BASE THEORIES NH3 is a BASE in water — and water is itself an ACID NH3 / NH4+ is a conjugate pair — related by the gain or loss of H+ Every acid has a conjugate base - and vice-versa.

  18. Conjugate Pairs

  19. You Practice • NH3 + H2O → NH4+ + OH- • HNO3 + NaOH → H2O + NaNO3 • NaHCO3 + HCl → NaCl + H2CO3

  20. Amphoteric • A substance having the ability to act as an acid or a base or AmphoPROTIC Hydrogen ion = proton • Water is an example

  21. Water is amphoprotic It can gain and lose a H+

  22. Hydronium ion – An ion formed when a free H+ forms with water to form an H3O+

  23. Why is Water Neutral? [H3O+ ] = [OH-] When one water gains, another loses a H+

  24. The pH scale only for water solutions Basic = more OH- Neutral H3O+ = OH- Acidic = more H3O+

  25. Relative ion concentrations • pH is a relative measure of the hydrogen ion concentration pH is a rating; ranges from 0 – 14 0 = most,7 equal, 14 = least

  26. Why at a pH = 7 ? • Determined by concentration [ X ] of each ion [H+ ]= [OH-] = 10-7M The concentration of hydrogen ion equals the concentration of hydroxide ion equals ten to the negative seventh molar concentration Need to remember molarity and concentration

  27. [H3O+], [OH-] and pH A common way to express acidity and basicity is with pH pH = - log [H3O+] In a neutral solution, [H3O+] = [OH-] = 1.00 x 10-7 at 25 oC pH = -log (1.00 x 10-7) = - (-7) = 7

  28. Relative ion concentrations • pOH is a relative measure of the hydroxide ion concentration pOH is a rating; ranges from 0 – 14 0 = most,7 equal, 14 = least

  29. Any pX Scales In general pX = -log X pOH = - log [OH-] pH = - log [H+]

  30. Determining pOH pH + pOH = 14 If know one can determine the other. If pH = 13, what is the pOH? 13 + pOH = 14 pOH = 14 – 13 = 1

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