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Chapter 16

Chapter 16. acids and bases. are acids important? boy howdy! lemons, heartburn, digestion, cavities, pools, cleaners, etc., etc., etc. sulfuric acid alone is used to make fertilizers, detergents, plastics, pharmaceuticals, batteries, metals… here we hit the highlights of acids and bases….

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Chapter 16

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  1. Chapter 16 acids and bases

  2. are acids important? boy howdy! • lemons, heartburn, digestion, cavities, pools, cleaners, etc., etc., etc. • sulfuric acid alone is used to make fertilizers, detergents, plastics, pharmaceuticals, batteries, metals… • here we hit the highlights of acids and bases…

  3. 16.1 acids and bases • acids were first known for their sour taste (think vit c, vinegar, lemons, vomit, underarm juice, orange juice, bad milk • bases (alkalis) are known for their bitter tastes, and slippery feel; most soaps are basic

  4. the arrhenius model • svante arrhenius was the first guy to try and figure out what was going on chemically; he found: • acids produced H+ ions in aq solns • bases give us hydroxide (OH-) ions

  5. 16.1 • HCl(g)H+(aq) + Cl-(aq)this is the strong acid (hydrochloric)or… • NaOH(s) Na+(aq) + OH-(aq)this is a strong base • but there is a better way of looking at it…

  6. the brønsted-lowry model • the brønsted way of things looked at it this way: • acids donate protons (H ions) • bases accept protons EZ!

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

  8. 16.1 • when the HA lost its H it went from acid to base; i.e. it cd get the H back at some other time • when an acid loses an H it becomes a conjugate base • when water gained a proton to become H3O+ it became an acid • called conjugate acid

  9. 16.1

  10. 16.1 • a conjugate acid-base pair differs just by one single H: • HCl/Cl- • H2O/H3O+ • NH4+/NH3 • BTW; H3O+ has a special name; hydronium ion

  11. 16.1 • can you see each of these rxns are acid-base rxns? • can you ID the conjugate pairs?

  12. 16.2 acid strength • some acids dump every H they can • they are completely ionized • = strong acids • some acids hold on tomost their Hs • they are only partiallyionized • = weak acid

  13. 16.2 strong weak

  14. 16.2 strong weak

  15. 16.2

  16. 16.2 • some acids have 2 protons that can be lost • = diprotic acid • e.g. H2SO4 • most acids are oxyacids, i.e. the proton to be lost is hooked up to an O • e.g. HNO3, HOCl, H2SO4, H3PO4

  17. 16.2 • some of the most common acids are organic acids which have a carboxyl group hooked up to them • –C–O–H || O • these critters are weak (e.g. acetic acid (vinegar), formic acid (ant bites), citric acid, vitamin C, aspirin

  18. 16.3 water as an acid and a base • water can accept a proton (to become hydronium), or… • donate a proton (to become hydroxide ion) • acts as both acid and base!!! • called amphoteric • water can actually self-ionize!…

  19. 16.3 H2O + H2O  H3O+ + OH– • this hardly happens at all (thankfully) • important toknow here thatit does happen,and even purewater has someacids and basesfloating around init…

  20. 16.3 • a soln is acidic if [H3O+] > [OH-] • a soln is basic if [H3O+] < [OH-] • a soln is neutral if [H3O+] = [OH-] • important to see here that whatever the soln is there’s always some of the enemy in there

  21. 16.4 the pH scale • fyi: [H3O+] is also known as [H+] • the pH scale is an easy way to see how acidic or basic a soln is • mathematically: pH = –log[H3O+] • if I give you the [H3O+] you can figure out the pH of the soln by: • entering the [H3O+], taking the log, and changing the sign (+/-)

  22. 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

  23. 16.4 • every change of one pH unit = 10x acidic concentration change • pH > 7 basic • pH = 7 neutral • pH < 7 acidic

  24. 16.4 • to find the [H3O+] from pH do opposite • enter pH; change sign; take inverse log! • so if pH is 8.53… • change sign (-8.53) • take inv log (3.0 x 10-9 M)

  25. 16.5 measuring pH • a couple ways we have to measure pH • one way involves indicators, things which change colors in the presence of different [H3O+]…

  26. 16.5 • some indicators can be put on paper, we can read colors to determine pH

  27. 16.5 • a really accurate way of doing it is with a pH meter

  28. 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?

  29. 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!!!

  30. 16.8 EOC questions • 45

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