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Acid and Bases

Acid and Bases. Acid and Bases. Some Properties of Acids. Produce H + (as H 3 O + ) ions in water (the hydronium ion is a hydrogen ion attached to a water molecule) Taste sour Corrode metals (react to  H 2 (g)) Are electrolytes (conduct electricity)

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Acid and Bases

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  1. Acid and Bases

  2. Acid and Bases

  3. Some Properties of Acids • Produce H+ (as H3O+) ions in water (the hydronium ion is a hydrogen ion attached to a water molecule) • Taste sour • Corrode metals (react to  H2 (g)) • Are electrolytes (conduct electricity) • React with bases to form a salt and water • pH is less than 7 • Turns blue litmus paper to red “Blue to Red A-CID”

  4. Some Properties of Bases • Produce OH- ions in water • Taste bitter, chalky • Are electrolytes (conduct electricity) • Feel soapy, slippery • React with acids to form salts and water • pH greater than 7 • Turns red litmus paper to blue “Basic Blue”

  5. Some Common Acids & Bases- (video) HCl Hydrochloric Acid Stomach acid HNO3 Nitric Acid Jewelry making H2SO4 Sulfuric Acid Paper making; Car batteries H3PO4 Phosphoric Acid Preservative in Coca-Cola NaOH Sodium hydroxide lye KOH Potassium hydroxide liquid soap Ba(OH)2 Barium hydroxide stabilizer for plastics Mg(OH)2 Magnesium hydroxide “MOM” Milk of magnesia Al(OH)3 Aluminum hydroxide Maalox (antacid)

  6. Acid/Base definitions • Definition #1: Arrhenius (traditional) Acids – produce H+ ions (or hydronium ions H3O+) Bases – produce OH- ions (problem: some bases don’t have hydroxide ions!)

  7. Arrhenius acid is a substance that produces H+ (H3O+) in water Arrhenius base is a substance that produces OH- in water

  8. Arrhenius Acids and Bases- (video) • Strong acid- ionizes completely in aqueous solution • Strong electrolytes • HCl, HNO3 • Weak acid- releases few hydrogen ions in aqueous solution • HCN and acetic acid (-COOH) • Strong base- ionizes completely in aqueous solution • Strong electrolytes • Weak base- releases few hydroxide ions in aqueous solution

  9. Strong and Weak Acids/Bases The strength of an acid (or base) is determined by the amount of IONIZATION. STRONG=100% IONIZED HNO3, HCl, H2SO4 and HClO4 are among the only strong acids.

  10. Strong and Weak Acids/Bases • Weak acids are much less than 100% ionized in water. One of the best known is acetic acid = CH3COOH

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

  12. 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 (l)  NH4+ (aq) + OH- (aq)

  13. Acid/Base Definitions- (video) • Definition #2: Brønsted – Lowry Acids – molecule or ion that is a proton donor Bases – molecule or ion that is a proton acceptor A “proton” is really just a hydrogen atom that has lost it’s electron!

  14. A Brønsted-Lowryacidis a proton donor A Brønsted-Lowrybaseis a proton acceptor conjugatebase conjugateacid base acid

  15. ACID-BASE THEORIES The Brønsted definition means NH3 is aBASEin water — and water is itself anACID

  16. Conjugate Pairs- (video)

  17. Acids & Base Definitions Definition #3 – Lewis Lewis acid - a substance that accepts an electron pair Lewis base - a substance that donates an electron pair

  18. Lewis Acids & Bases Formation ofhydronium ion is also an excellent example. • Electron pair of the new O-H bond originates on the Lewis base.

  19. SUMMARY

  20. Acid Rain • NO, NO2, CO2, SO2, and SO3 gases from industrial processes can dissolve in atmospheric water to produce acidic solutions. • Burning of fossil fuels by coal-burning power plants, factories, and automobiles • Very acidic rain is known asacid rain. • Acid rain can erode statues and affect ecosystems. example:

  21. Acid Rain

  22. Amphoteric Compounds • Any species that can react as either an acid or a base is described asamphoteric. • example:water • water can act as a base acid1 base2 acid2 base1 • water can act as an acid base1 acid2 acid1 base2

  23. More About Water H2O can function as both an ACID and a BASE. In pure water there can beAUTOIONIZATION Equilibrium constant for water = Kw Kw = [H3O+] [OH-] =1.00 x 10-14at 25 oC

  24. Self-ionization or Autoionization of Water • In the self-ionization of water,two water molecules produce a hydronium ion and a hydroxide ion by transfer of a proton. -

  25. Relationship of [H3O+] to [OH–]

  26. More About Water Autoionization Kw= ionization constant of water Kw = [H3O+] [OH-] = 1.00 x 10-14 at 25 oC In a neutral solution [H3O+] = [OH-] so Kw = [H3O+]2 = [OH-]2 and so [H3O+] = [OH-] = 1.00 x 10-7 M

  27. Kw: the Constant of Water or How to find the missing # Kw = [H+1][OH-1] = 1E-14 Used to find unknown [H+1] or [OH-1] if the other is known or given If [H+1] = .0003M, find the [OH-1] 1E-14 = [.0003M] [OH-1] [OH-1]=3.33E-11M

  28. The pH scale is a way of expressing the strength of acids and bases. Instead of using very small numbers, we just use pH

  29. Logarithms • Base 10 logarithms (log) • The log of a number is the power to which 10 must be raised to get that number • log 1000 = 3 because 103 = 1000 • log 0.1 = -1 because 10-1 = 0.1 • Use your calculator to solve • log (1.25*10-3) = -2.90 • -log (3.64*10-12) = 11.44

  30. Calculating the pH pH = - log [H+] Example: If [H+] =1E-10pH = - log( 1E-10) pH = - (- 10) pH = 10 Example: If [H+] = 1.8E-5pH = - log 1.8E-5 pH = - (- 4.74) pH = 4.74

  31. pH Values as Specified [H3O+]

  32. Try These! Find the pH of these: • A 0.15 M solution of Hydrochloric acid (answer: .8239) 2) A 3.00 X 10-7 M solution of Nitric acid (answer: 6.5229) STOP

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

  34. pH calculations – Solving for H+ • A solution has a pH of 8.5. What is the Molarity of hydrogen ions in the solution? pH = - log [H+] 8.5 = - log [H+] -8.5 = log [H+] Antilog -8.5 = antilog (log [H+]) 10-8.5 = [H+] 3.16E-9 M = [H+]

  35. Using Logarithms in pH Calculations

  36. pOH • Since acids and bases are opposites, pH and pOH are opposites! • pOH does not really exist, but it is useful for changing bases to pH. • pOH looks at the perspective of a base pOH = - log [OH-] Since pH and pOH are on opposite ends, pH + pOH = 14

  37. [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

  38. The OH- ion concentration of a blood sample is 2.5 x 10-7 M. What is the pH of the blood? (answer: 7.3979) The pH of rainwater collected in a certain region of the northeastern United States on a particular day was 4.82. What is the H+ ion concentration of the rainwater? (answer: 1.51E-5M)

  39. Calculating [H3O+], pH, [OH-], and pOH Problem 1: Calculate the [H3O+], pH, [OH-], and pOH of a solution of 0.0024 Mhydrochloric acid at 25°C. [H3O+]= 0.0024 M pH= 2.62 [OH-]= 4.17 E^-12M pOH= 11.38 End

  40. Problem 2: What is the [H3O+], [OH-], and pOH of a solution with pH = 3.67? Is this an acid, base, or neutral? • [H3O+]= 10^ -3.67 = 2.14E-4 M • [OH-]= 10^-14 / (2.14E-4) = 4.67E-11 M • pOH= 14 – 3.67 = 10.33 • Acid

  41. pH meter • Tests the voltage of the electrolyte • Voltage changes as hydronium ion concentration changes • Converts the voltage to pH • Very cheap, accurate • Must be calibrated with a buffer solution

  42. pH indicators • Indicators are compounds that will change color in the presence of an acid or base. • Indicators are either weak acids or weak bases • Indicators only work in a specific range of pH • Some dyes are natural, like radish skin or red cabbage

  43. Neutralization ReactionsStrong Acid-Strong Base Neutralization • In aqueous solutions,neutralizationis the reaction of hydronium ions and hydroxide ions to form water molecules. • H3O+(aq) + OH(aq)  2H2O(l) • Asalt is an ionic compound composed of a cation from a base and an anion from an acid.

  44. Titration • Titration is the controlled addition and measurement of the amount of a solution of known concentration required to react completely with a measured amount of a solution of unknown concentration. • The point at which the two solutions used in a titration are present in chemically equivalent amounts is the equivalence point. • The point in a titration at which an indicator changes color is called the end point of the indicator.

  45. Setup for titrating an acid with a base

  46. Titration Curve for a Strong Acid and a Strong Base

  47. Titration Curve for a Weak Acid and a Strong Base

  48. Titration 1. Add solution from the buret to the flask. 2. Reagent (base) reacts with compound (acid) in solution in the flask. • Indicator shows when exact stoichiometric reaction has occurred. (Acid = Base) This is called the END POINT where NEUTRALIZATION has occurred. Titration Math(short version) M1• V1 = M2 • V2 Moles H3O+ = Moles OH-

  49. BURET Standard Solution = NaOH Solution of Unknown Concentration = HCl

  50. Titration using a pH Meter • Set up the buret and the chemicals the same except no Phenolphthalein is added • Set up the Nova with a pH sensor attached and insert the probe into the Unknown solution. Proceed with the addition of the base solution until the graph looks like the one attached • The volume where the large jump takes place is the End Point, moles Base=moles Acid • Begin calculations

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