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Bases

Acids. and. Bases. What are acids? Why are they important? What are bases? Why are they important? Which is dangerous? Acids or Bases?. 16.1 acids and bases. acids from the Latin acidus (sour)

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Bases

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  1. Acids and Bases

  2. What are acids? • Why are they important? • What are bases? • Why are they important? • Which is dangerous? Acids or Bases?

  3. 16.1 acids and bases • acids from the Latin acidus (sour) • bases (a.k.a. alkalis) are known for their bitter tastes, and slippery feel; most soaps are basic

  4. the arrhenius model • Svante Arrhenius • acids produce H+ ions in aqueous solutions • bases produce OH- (hydroxide) ions in aqueous solutions

  5. 16.1 Example • HCl(g)H+(aq) + Cl-(aq) or • HCl(g) +H2O H3O+(aq) + Cl-(aq)this is a strong acid • NaOH(s) Na+(aq) + OH-(aq)this is a strong base

  6. the Brønsted-Lowry model • The Arrhenius concept is limited because the only base is hydroxide (OH-) • Bronsted and Lowry both formulated a better explanation • acids donate protons (H+) • bases accept protons (H+)

  7. 16.1 • assume our acid is HA; then… • HA + H2O  H3O+ + A- • The HA lost an H+ (proton); it acted acidic • The water gained a proton; it acted as a base

  8. 16.1 • when an acid loses an H+ it becomes a conjugate base • when a base gains an H+ it becomes a conjugate acid

  9. + + + H H O H O Cl Cl H H H The Bronsted-Lowry concept • In this idea, the ionization of an acid by water is just one example of an acid-base reaction. conjugate acid conjugate base acid base conjugate acid-base pairs • Acids and bases are identified based on whether they donate or accept H+. • “Conjugate” acids and bases are found on the products side of the equation. A conjugate base is the same as the starting acid minus H+.

  10. 16.1 • a conjugate acid-base pair differs just by one single H+: • HCl/Cl- • H2O/H3O+ • NH4+/NH3

  11. Conjugate Acid base pairs Identify the acid, base, conjugate acid, conjugate base, and conjugate acid-base pairs: HC2H3O2(aq) + H2O(l)  C2H3O2–(aq) + H3O+(aq) conjugate base conjugate acid acid base conjugate acid-base pairs OH–(aq) + HCO3–(aq)  CO32–(aq) + H2O(l) base acid conjugate base conjugate acid conjugate acid-base pairs

  12. Practice HF(aq) + SO32–(aq)  F–(aq) + HSO3–(aq) (a) conjugate base conjugate acid acid base conjugate acid-base pairs (b) CO32–(aq)+HC2H3O2(aq)C2H3O2–(aq)+HCO3–(aq) base acid conjugate base conjugate acid conjugate acid-base pairs (c) H3PO4(aq) + OCl–(aq)  H2PO4–(aq) + HOCl(aq) conjugate base conjugate acid acid base conjugate acid-base pairs

  13. 16.2 acid strength • Find the Conjugate acid or base of the following • Find the acid of NO3- • Find the base ofHCO3-

  14. 16.2 acid strength • strong acids give up every H they can, they are completely ionized • HCl H+ + Cl- • weak acids hold on to most of their H, they are only partially ionized. • H2CO3 H+ + HCO3-

  15. The strong acids are : • HCl, HBr, HI, HNO3, H2SO4, HClO4 • All other acids are weak • Ex. H3PO4 is weak because it does not completely ionize and it is not one of the 6 strong acids.

  16. 16.2 acid strength strong basescompletely ionize and form OH- Strong bases include group 1(Alkali metal) hydroxides, Sr(OH)2, Ca(OH)2 and Ba(OH)2.  All others are weak. Strong NaOH Weak CuOH NaOHNa+ + OH- CuOHCu+ + OH- Weak bases do not completely ionize.

  17. 16.2 strong weak

  18. 16.2 strong weak

  19. Identify if the following are strong or weak acids/bases and state whether a light bulb will be bright, dim or dark. • NaOH • HC2H3O2 • HF • HCl • H2C2O4 • Fe(OH)2 • CH3CH2OH

  20. 16.2 acid ionization flash.swf

  21. 16.2 • diprotic acids have 2 protons that can be lost (e.g. H2SO4) • H3PO4 is triprotic. • Oxyacids: the proton to be lost is hooked up to an O (e.g. HNO3, HOCl, H2SO4, H3PO4) The more O’s in the formula, the stronger the acid.

  22. 16.2 • organic acids carbon-containing chemicals with acid properties; most common are carboxylic acids –C–O–H || O • they are weak (e.g. acetic acid (vinegar), formic acid (ant bites), citric acid, vitamin C, aspirin)

  23. 16.3 water as an acid and a base • Water is amphoteric (acts as both acid and base) • It can accept a proton (to become hydronium), or • donate a proton (to become hydroxide ion)

  24. 16.3 H2O + H2O  H3O+ + OH– • Because of this even purewater has someacids and basesin it

  25. How ‘acid’ or ‘basic’ is it? Acidic Solutions = Hydronium ion concentration is greater than hydroxide ion concentration Basic Solutions = Hydroxide concentration is greater than hydronium ion concentration

  26. 16.3 • a solution is acidic if [H3O+] > [OH-] • a solution is basic if [H3O+] < [OH-] • a solution is neutral if [H3O+] = [OH-] • The brackets [ ] mean concentration What are the units for concentration? M, moles/liter

  27. 16.4 the pH scale • What does pH mean? • the pH scale is an easy way to see how acidic or basic a solution is • mathematically: pH = –log[H3O+] • A pH of 7 is 10-7 mol/liter or 10-7 M H3O+ • if you know the [H3O+] you can figure out the pH of the solution by: entering the [H3O+], taking the log, and changing the sign (+/-)

  28. example • what is the pH if the [H3O+] = 0.001 M • pH = 3 • pH if the [H3O+] = 0.000021 M • pH = 4.68 • pH if the [H3O+] = 0.000000059 M • pH = 7.23

  29. 16.4 • every change of one pH unit = 10x acidic concentration change • pH > 7 basic • pH = 7 neutral • pH < 7 acidic

  30. 16.4 • to find the [H3O+] from pH, do the opposite • enter pH; change sign; take inverse log (10^…) • so if pH is 8.53 • change sign (-8.53) • take inv log 10^(-8.53) = (3.0 x 10-9 M) = 0.000000003 M

  31. Water • Water ionizes- falls apart into ions. • H2O  H+ + OH- • Called the self ionization of water. • Only a small amount. • [H+ ] = [OH-] = 1 x 10-7M • A neutral solution. • In water Kw = [H+ ] x [OH-] = 1 x 10-14 • Kw is called the ion product constant.

  32. Ion Product Constant • H2O  H+ + OH- • Kw is constant in every aqueous. solution [H+] x [OH-] = 1 x 10-14 M2 • If [H+] > 10-7 then [OH-] < 10-7 • If [H+] < 10-7 then [OH-] > 10-7 • If we know one, we can determine the other. • If [H+] > 10-7 acidic [OH-] < 10-7 • If [H+] < 10-7 basic [OH-] > 10-7

  33. pH and pOH These are the most useful…. • pH = - log [H+] • pOH = - log [OH-] • pH + pOH = 14 • [H+] x [OH-] = 1.0 x 10 -14

  34. pH and pOH Calculations pH + pOH = 14 [H+] [OH-] = 1 x 10-14

  35. 1. If the pOH of a solution is 5.25, what is pH? 2. What is the pH of a solution with a pOH of 4? 3. What is the [H+] of a solution with a [OH-] of 1.0 x10 – 4 4. If the pH is 2.7, what is the [H+] ? 5. What is the [OH-] of a solution with a pH of 10? = 5. x 10 -6

  36. Strong acids have the same [H+] as the acid (so do bases with [OH-] • Calculate the pH of a 0.25 M HCl solution. • Calculate the pH of a 0.10 M NaOH solution. So [H+]= 0.25 M HCl  H+ + Cl- pH= - Log (0.25) = 0.60 So [OH-] = 0.10 M NaOH  Na+ + OH- pOH= - Log (0.10) = 1, so pH = 14 -1 = 13

  37. 16.5 measuring pH pH can be measured in several ways one way involves indicators, things which change colors in the presence of different H3O+ concentrations

  38. 16.5 some indicators can be put on paper, we can read colors to determine pH

  39. 16.5 a really accurate way of doing it is with a pH meter

  40. Neutralization Reactions • Acid + Base  Salt + water • Salt = an ionic compound • Water = HOH • HNO3 + KOH  • HCl + Mg(OH)2 • H2SO4 + NaOH  • Really just double replacement.

  41. Titration • When you add the same number of moles of acid and base, the solution is neutral. • By measuring the amount of a base added you can determine the concentration of the acid. • If you know the concentration of the base. • This is a titration.

  42. Titration equations • Ma x Va x # of H+ = Mb x Vb x # of OH- moles of H+ = moles of OH-

  43. More Practice • If it takes 45 mL of a 1.0 M NaOH solution to neutralize 57 mL of HCl, what is the concentration of the HCl ? • If it takes 67 mL of 0.500 M HF to neutralize 15mL of NaOH what was the concentration of the NaOH ? • How much of a 0.275 M HCl will be needed to neutralize 25mL of .154 M NaOH?

  44. 16.8 buffered solutions a buffered soln resists a change in pH even when a strong acid or base is put in it especially important to living critters whose bio systems require a cnst pH how does it work?

  45. 16.8 a soln contains a weak acid HA, and its conjugate base A- when we dump in extra acid or base these two gobble it up: the A- reacts with the xs protons to become HA the HA reacts with the xs OH- to become A- overall there is little change in pH!!!

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