The Chemistry of Acids and Bases

1. The Chemistry of Acids and Bases

2. Acids and Bases: Define and Calculate pH/pOHAt the conclusion of our time together, you should be able to: Define pH and pOH Explain the pH scale and what it means Change any pH reading to pOH Convert pH to concentration of hydronium ion concentrations, hydronium ion concentrations to pH

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4. The pH scale is a way of expressing the strength of acids and bases. This scale is defined by:pH = - log [H+] Under 7 = acid 7 = neutral Over 7 = base What is pH???

5. What is pH??? p = count H = Hydronium ion (H3O+) In 1 Liter of water, (55+ moles of water), how many moles of hydronium ions are there??? Understanding pH gives me this number!!! If there was 1 mole of H3O+in 1 Liter of water, (55+ moles of water), this count would be 1 mole.

6. What is pH??? Remember: pH = - log [H+] pH = -log[1] Therefore, by definition, the pH of this solution is = 0

7. What is the pH of water??? H2O + H2O ---> H3O+ + OH- <=== This equation indicates that most water molecules stay as molecules, very few will form hydronium ions If we count the number of hydrogen ions in one liter of water (pH) we would get: .0000001 moles of H3O+/liter of water or 10-7 moles of H3O+/liter of water What is the pH of water?? pH = 7

8. What is the pOH of water??? H2O + H2O ---> H3O+ + OH- <=== This equation indicates that most water molecules stay as molecules, very few will form hydroxide ions If we count the number of hydroxide ions in one liter of water (pOH) we would get: .0000001 moles of OH-/liter of water or 10-7 moles of OH-/liter of water What is the pOH of water?? pOH = 7

9. How High is the pH Scale?? Since 1 mole of OH- in one Liter of water would be a pOH = 0 And the pH and pOH of water is 7 or neutral, Therefore, the pH of a strong base with a pOH of 0 would be? pH = 14 Therefore, the pH scale goes from 0-14 Also, any pH can be converted to pOH by? Subtracting from 14.

10. pH- The Amount Of H+ Ions In A Solution. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 ACID extra H+1 ions (protons) BASE fewer H+1 ions. extra OH-1 ions.

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13. Examples of Converting pH If an acid has a pH of 3, what would be the pOH? 14 – 3 = 11 If an base has a pOH of 2, what would be the pH? 14 – 2 = 12

14. Calculating the pH pH = - log [H+] (Remember that the [ ] mean Molarity) Example: If [H+] = 1 X 10-10pH = - log 1 X 10-10 pH = 10 Example: If [H+] = 1.80 X 10-5pH = - log 1.80 X 10-5 pH = 4.7

15. Try These! pH = 0.82 pH = 6.5 Find the pH of these: • A 0.15 M solution of Hydrochloric acid 2) A 3.00 X 10-7 M solution of Nitric acid

16. But Why Only 2 Significant Figures?? pH = 6.5 Remember, we are working with logarithms. Therefore, we will use the pHAD principle. Add significant figures after the Decimal Point for pH. 2) A 3.00 X 10-7 M solution of Nitric acid

17. pH Calculations – Solving for H+ If the pH of Coke is 3.12, [H+] = ??? Because pH = - log [H+] then - pH = log [H+] Divide both sides by log or Take antilog (10x) of both sides and get 10-pH=[H+] 10-3.12 = [H+] = 7.6 x 10-4 M *** to find antilog on your calculator, press “Shift” or “2nd function” and then the log button

18. pH Calculations – Solving for H+ pH = -log [H+] 3.78 = -log [H+] -3.78 = log [H+] Inverse log -3.78 = inverse log (log [H+]) 10-3.78 = [H+] 1.66 x 10-4 = [H+] A solution has a pH of 3.78. What is the concentration of hydrogen ions in the solution? (#1 on handout)

19. What is the pOH? If an acid has a pH of 3.78, what would be the pOH? (#1 on handout) 14 – 3.78 = 10.22

20. pH Calculations – Solving for H+ pOH = - log [OH-] 10.22 = - log [OH- ] - 10.22 = log [OH- ] Inverse log -10.22 = inverse log (log [OH- ]) 10-10.22 = [OH-] 6.03 x 10-11 = [OH-] A solution has a pH of 3.78. What is the concentration of hydroxide ions in the solution? (#1 on handout)

21. Calculating [H3O+], pH, [OH-], and pOH Problem 1: What is the [H3O+], [OH-], and pOH of a solution with pH = 3.78? Is this an acid, base, or neutral? [H3O+] = 1.66 x 10-4 M pOH = 10.22 [OH-] = 6.03 x 10-11 M Acid

22. Calculating the pOH pOH = - log [OH-] (Remember that the [ ] mean Molarity) Example #4 on handout: If [OH-] = 4.88 x 10-6pOH = - log (4.88 x 10-6) pOH = 5.31

23. Calculating [H3O+], pH, [OH-], and pOH Problem 2: A chemist dilutes concentrated hydrochloric acid to make: 0.000 389 M HCl. Calculate the pH, [OH-], and pOH pH = 3.41 pOH = 10.59 [OH-] = 2.57 x 10-11 M Acid

24. [OH-] 1.0 x 10-14 [OH-] 10-pOH 1.0 x 10-14 [H+] -Log[OH-] [H+] pOH 10-pH 14 - pOH -Log[H+] 14 - pH pH

25. pH [H+] [OH-] pOH

26. Acids and Bases: Define and Calculate pH/pOHLet’s see if you can: Define pH and pOH Explain the pH scale and what it means Change any pH reading to pOH Convert pH to concentration of hydronium ion concentrations, hydronium ion concentrations to pH

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31. The “p” in pH stands for? • Priority • Count • Number • Molarity • Not listed

32. The “H” in pH stands for? • House • Hydrogen ions • Acid • Concentration • Not listed

33. If a solution has a pH of 6.5, what is the pOH of that same solution? • 4.5 • 7.5 • 6.5 • 0.0 • 12.5 • Not listed

34. If a solution has a pH of 6.2, what is the [H+] of that solution? • 6.2 • 6.3 x 10-7 • 1.0 x 106.2 • 1.0 x 107.8 • 7.8 • Not listed

35. If a solution has a pOH of 9.44, what is the [OH-] of that same solution? • 0.98 • 1.00 x 109.44 • 3.63 x 10-10 • 4.56 • 9.44 • Not listed

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37. The Chemistry of Acids and Bases

38. Acids and Bases: Strength and IndicatorsAt the conclusion of our time together, you should be able to: Determine the relative strength of acids and bases and the reason for the strengths List the 3 basic types of indicators Explain each indicator’s strengths and weaknesses Use an appropriate indicator to determine the pH of a substance

39. Remember: the pH scale is a way of expressing the strength of acids and bases. Under 7 = acid 7 = neutral Over 7 = baseWhat makes an acid strong or weak??

40. Strong or Weak Acids/Bases The strength of an acid (or base) is determined by the amount of IONIZATION. HNO3, HCl, H2SO4 and HClO4 are among the only known strong acids.

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

42. Weak Acids • Weak acidsare much less than 100% ionized in water. One of the best known is acetic acid = CH3CO2H

43. Strong ACID HCl Hydrochloric acid H2SO4 Sulfuric acid HNO3 Nitric acid Weak ACID CH3COOH Acetic acid H2CO3 Carbonic acid Citric acid

44. CaO Strong Bases Other common strong bases include KOH andCa(OH)2. CaO (lime) + H2O --> Ca(OH)2 (slaked lime) Strong Base:100% dissociated in water. NaOH (aq) ---> Na+ (aq) + OH- (aq)

45. Weak base:less than 100% ionized in water One of the best known weak bases is ammonia NH3 (aq) + H2O (l) NH4+ (aq) + OH- (aq) Weak Bases

46. Weak Bases

47. Strong or Weak Acids/Bases Summary • Strong acids and bases dissolve in water • Hydrochloric, Hydrobromic, Hydroiodic, • (All Binaries) • Nitric, Sulfuric, Perchloric Acids • (Ternary Acids with 2 more O than H) • Group I hydroxides

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49. There are Several Ways to Test for pH • There are three basic types: • Paper • pH meter • Liquid indicators • (Some are natural liquid indicators like red cabbage, radishes)

50. Paper Testing Paper tests like litmus paper and pH paper Put a stirring rod into the solution and stir. Take the stirring rod out, and place a drop of the solution from the end of the stirring rod onto a piece of the paper Read and record the color change. Note what the color indicates. Use a small portion of the paper. You can use one piece of paper for several tests.