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Acids and Bases Chapter 19

Acids and Bases Chapter 19. 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-this ion determines pH) Taste sour (like vinegar) Corrode metals Electrolytes React with bases to form a salt and water

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Acids and Bases Chapter 19

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  1. Acids and BasesChapter 19

  2. Some Properties of Acids • Produce H+ (as H3O+) ions in water (the hydronium ion is a hydrogen ion attached to a water molecule-this ion determines pH) • Taste sour (like vinegar) • Corrode metals • Electrolytes • React with bases to form a salt and water • pH is less than 7 • Turns blue litmus paper to red “Blue to Red Ah-CeD” • Indicator-phenolphathalein-remains clear • Indicator-cabbage juice-turns red/violet

  3. Acid Nomenclature Flowchart

  4. Acid Nomenclature Review • HBr (aq) • H2CO3 • H2SO3 hydrobromicacid  carbonicacid  sulfurousacid

  5. Name ‘Em! • HI (aq) • HCl (aq) • H2SO3 • HNO3 • HIO4 • Hydroiodic Acid • Hydrobromic Acid • Sulfuric Acid • Nitric Acid • Iodic Acid

  6. Some Properties of Bases • Produce OH- ions in water • Taste bitter, chalky • Are electrolytes • Feel soapy, slippery • React with acids to form salts and water • pH greater than 7 • Turns red litmus paper to blue “Basic Blue” • Indicator-phenolphathalein-turns pink • Indicator-cabbage juice-turns green/yellow

  7. Some Common Bases 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)

  8. The pH scale is a way of expressing the strength of acids and bases. Instead of using very small numbers, we just use the NEGATIVE power of 10 on the Molarity of the H+ (or OH-) ion.Under 7 = acid 7 = neutral Over 7 = base

  9. pH of Common Substances

  10. Calculating the pH pH = - log [H+] or –log[H3O] Remember that the [ ] means concentration/molarityStrong Acids have a [H3O+] equal to their molarity because they 100% disassociate Example: If [H+] = 1 X 10-10 MpH = - log (1 X 10-10) pH = - (- 10) pH = 10 (Base) Example: If [H+] = 1.8 X 10-5 MpH = - log (1.8 X 10-5) pH = - (- 4.74) pH = 4.74 (Acid)

  11. Try These! Find the pH of these: 1) A 0.15 M solution of Hydrochloric acid (100% disassociates) pH = -log(0.15) = 0.82 This is less than 7, so it’s a (strong) acid 2) A 3.00 X 10-7 M solution of Nitric acid pH = -log(3.00 x 10-7 ) = 6.52 This is barely less than 7, so it’s a (weak) acid

  12. 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

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

  14. 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

  15. Comparing pH, pOH and Concentrations pH [H+] [OH-] pOH

  16. [H3O+], [OH-] and pH What is the pH of a NaOH solution if [OH-] = 0.0010 (or 1.0 X 10-3 M)? pOH = - log 0.0010 pOH = 3 So pH = 14 – 3 = 11 This is a base!

  17. The OH- ion concentration of a blood sample is 2.5 x 10-7 M. What is the pH of the blood? 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? pH = -log [H+] 4.82 = -log [H+] 1 x 10-4.82 = [H+] 1.51 x 10-5= [H+] pOH = -log [OH-] pOH = -log 2.5 x 10-7 pOH = 6.6 pH + pOH = 14so 14 – 6.6 =7.4 (Nearly Basic)

  18. [OH-] 1.0 x 10-14 [OH-] 10-pOH 1.0 x 10-14 [H+] -Log[OH-] For Strong AcidsMolarity = H+ Ion concentration [H+] pOH For Strong BasesMolarity = OH- Ion concentration 10-pH 14 - pOH -Log[H+] 14 - pH pH

  19. Calculating [H3O+], pH, [OH-], and pOH Problem 1: A chemist dilutes concentrated hydrochloric acid to make two solutions: (a) 0.030 M and (b) 0.0024 M. Calculate the [H3O+], pH, [OH-], and pOH of the two solutions at 25°C. Problem 2: What is the [H3O+], [OH-], and pOH of a solution with pH = 3.67? Is this an acid, base, or neutral? Problem 3: Problem #2 with pH = 8.05? • [H3O+]= 0.03M strong acid • [OH-]=10-14/[H3O+]= 3.3x10-13 M • pH=- log [H3O+]= 1.5 • pOH=- log[OH]= 12.5 b. [H3O+]= .0024 strong acid [OH-]=10-14/[H3O+]= 4.2x10-12 M pH=- log [H3O+]= 2.6 pOH=- log[OH]= 11 [H3O+]=10-3.67= 0.00021M [OH-]=10-14/[H3O+]= 4.8x10-11 M pOH=- log[OH]= 10. Base(Weak) [H3O+]= 10-8.05= 8.9 x 10-9 M [OH-]=10-14/[H3O+]= 1.1 x 10-6 M pOH=- log[OH]= 5.9 Acid(Weak)

  20. Strong and Weak Acids/Bases The strength of an acid (or base) is determined by the amount of IONIZATION, not by concentration! HNO3, HCl, H2SO4 and HClO4 are among the only known strong acids.

  21. Strong and Weak Acids/Bases Generally acids and bases are either STRONG or WEAK. STRONG ACID: HNO3 (aq) + H2O (l) → H3O+ (aq) + NO3- (aq) HNO3 is about 100% dissociated in water. It’s molarity in solution will equal its [H3O+].

  22. Strong and Weak Acids/Bases Weak acids are much less than 100% ionized in water. This has nothing to do with concentration. The moles/L (molarity of solution) doesn’t equal the ion concentration One of the best known is acetic acid = CH3CO2H

  23. CaO Strong and Weak Acids/Bases • Strong Base:100% dissociated in water. This has NOTHING to do with concentration! • The ion concentration, [OH-] = mol/L, molarity of solution ex: NaOH (aq) → Na+ (aq) + OH- (aq) Other common strong bases include KOH andCa(OH)2. CaO (lime) + H2O → Ca(OH)2 (slaked lime)

  24. Strong and Weak Acids/Bases • Weak base:less than 100% ionized in water. Concentration of solution in mol/L doesn’t equal the [OH-], ion concentration One of the best known weak bases is ammonia NH3 (aq) + H2O (l)  NH4+ (aq) + OH- (aq)

  25. pH testing There are several ways to test pH • Blue litmus paper (red = acid) • Red litmus paper (blue = basic) • pH paper (multi-colored) • pH meter (7 is neutral, <7 acid, >7 base) • Universal indicator (multi-colored) • Indicators like phenolphthalein • Natural indicators like red cabbage, radishes

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

  27. 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!)

  28. Acid/Base Definitions • Definition #2: Brønsted – Lowry Acids – proton donor Bases – proton acceptor A “proton” is really just a hydrogen atom that has lost it’s electron!

  29. ACID-BASE THEORIES The Brønsted definition means NH3 is aBASEin water — and water is itself anACID Base Acid ConjugateAcid ConjugateBase

  30. Conjugate Pairs of Brønsted-Lowry

  31. Learning Check! Draw a line connecting the conjugate pairs: Label the acid, base, conjugate acid, and conjugate base in each reaction: HCl + OH-   Cl- + H2O Acid Base Conj.Base Conj.Acid H2O + H2SO4   HSO4- + H3O+ Conj.Base Conj.Acid Base Acid

  32. Acids & Base Definitions Definition #3 – Lewis Lewis acid - a substance that accepts an electron pair to form a covalent bond Lewis base - a substance that donates an electron pair to form a covalent bond Electron pair of the new O-H bond originates on the Lewis base Example:

  33. Lewis Acid/Base Reaction Example: Example:

  34. moles solute ( M ) = Molarity liters of solution Concentration of Solute The amount of solute in a solution is given by its concentration.

  35. PROBLEM: Dissolve 5.00 g of NiCl2 in enough water to make 250 mL of solution. Calculate the Molarity. Step 1: Calculate moles of NiCl2 5.00 g NiCl2 1 mol NiCl2 = 0.0386 mol NiCl2 129.59 g NiCl2 Step 2: Calculate Molarity 0.0386 mol NiCl2 = 0.154 M NiCl2 0.250 L [NiCl2] = 0.154 M Substance is written in brackets to indicate concentration!

  36. USING MOLARITY What mass of oxalic acid, H2C2O4, is required to make 250. mL of a 0.0500 M solution? Step 1: Change mL to L. 250 mL * 1L/1000mL = 0.250 L Step 2: Calculate. Moles = (0.0500 mol/L) (0.250 L) = 0.0125 moles Step 3: Convert moles to grams. (0.0125 mol)(90.00 g/mol) = 1.13 g moles = M•V

  37. Learning Check How many grams of NaOH are required to prepare 400. mL of 3.0 M NaOH solution? Step 1: Change mL to L. 400. mL * 1L/1000mL = 0.400 L Step 2: Calculate. Moles = (3.0 mol/L) (0.400 L) = 1.2 moles Step 3: Convert moles to grams. (1.2 mol )(40.00 g/mol) = 48 g

  38. Preparing Solutions • Weigh out a solid solute and dissolve in a given quantity of solvent. • Dilute a concentrated (stock) solution to give one that is less concentrated. To determine how to dilute, use: M1V1 = M2V2

  39. Example Dilution Problem M1 = concentration of the 1st solutionV1 = volume of the 1st solutionM2 = concentration of the 2nd solutionV2 = volume of the 2nd solution M1V1 = M2V2 You have 1 L of a 0.125 M aqueous solution of table sugar.  You want to dilute the solution to 0.05 M.  What do you do? (0.125 M) (1 L) = (0.05 M) V2 so 2.5 L = V2 Add enough water to the first solution so that the solution's volume becomes 2.5 L What do you think happens to the color when you dilute? LessIntense

  40. 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 10-14M2at 25 oC

  41. Oxalic acid, H2C2O4 ACID-BASE REACTIONSNeutralization! Acid H2C2O4(aq) + 2 NaOH(aq) → Na2C2O4(aq) + 2 H2O(l) Base Salt(neutral pH) Water(neutral pH) This reaction is called a TITRATION.

  42. Setup for titrating an acid with a base

  43. Titration 1. Add solution from the buret. 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 NEUTRALIZATION.

  44. LAB PROBLEM: Standardize a solution of NaOH — i.e., accurately determine its concentration. 35.62 mL of NaOH is neutralized with 25.2 mL of 0.0998 M HCl by titration to an equivalence point. What is the concentration of the NaOH? Known:Molarity (Base) = ? Volume (Base) = 35.62 mL = 0.03562 LMolarity (Acid) = 0.0998 M Volume (Acid) = 25.2 mL = 0.0252 L Equation: HCl + NaOH → NaCl + H2O Mole Ratio: 1 mol HCl 1 mol NaOH Find molesNaOH Molarity of NaOH = mol NaOH = 0.0025 mol = 0.0706 M L 0.03562 L

  45. The End

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