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Acids & Bases

Learn about the properties of acids and bases, the difference between strong and weak acids/bases, and how to calculate pH.

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Acids & Bases

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  1. Acids & Bases

  2. Properties of Acids • Taste SOUR (ex: lemons, vinegar) • Corrosive to Metals • Produces H+ ions • Which is the same as H3O+ (hydronium ion) • Proton (H+) Donor • Example: HCl + H2O  Cl- + H3O+

  3. Strong Acid vs Weak Acid Strong Acid – an acid that completely dissociates to produce H+ ions in solution (lot of H+) • HCl, HNO3 Weak Acid – an acid that dissociates to a slight extent in aqueous solution (not that many H+) • HC2H3O2 (vinegar), lemon juice

  4. Strong Acids vs. Weak Acids

  5. Indicators • An indicator is a chemical that will changecolors when placed in an acidic, basic or neutral environment Indicator Colors for Acids Litmus paper = red Phenolphthalein = clear Methyl orange = red

  6. Properties of Bases • Tastes Bitter (banana peel, dark chocolate, parsley) • Feels slippery (soap) • Produces OH- ions • Proton (H+) Acceptor • Example: NH3 + H2O  NH4+ + OH -

  7. Strong Bases v. Weak Bases Strong Base – a base that completely dissociates to produce many OH- ions in solution • NaOH, KOH Weak Base – a base that dissociates to a slight extent in aqueous solution (not that many OH-) • NH3 (ammonia) Strength & Weaknesses of A & B Video

  8. Indicators Indicator Colors for Bases Litmus paper = blue Phenolphthalein = pink Methyl orange = yellow

  9. Measuring the Amount of H+ and OH− Ions in a Solution pH concentration _____ Scale- measures the _____________ of [H+] ions in a solution _____ Scale- measures the concentration of [ ____ ] ions in a solution With the pH scale, we have another way to define acids and bases: Acids have a pH _________7.0 Bases have a pH _________7.0 Neutral pH ___7.0 pOH OH− below Neutral above = Acidic Basic

  10. pH of different household items • Make predictions on whether a solution would be acidic, basic or neutral • Go around the room, checking each cup with pH paper (make sure used pH paper goes in GARBAGE!)  to save pH paper, use HALF a side for each one. • Approximate pH colors: purple-ish red (pH 2) red (pH 4) brown (pH 6) Stays the same (pH 7) green (pH 8) blue (pH 10)

  11. Examples of Common Acids citrus aspirin Pepsi, _________ juices, ___________, stomach acid, battery acid, _____________, ______ vinegar DNA

  12. Examples of Common Bases ammonia Milk of magnesia, ___________, drain cleaner, soap, blood, ____________ tablets, ___________ ________. antacid baking soda

  13. Acids & Bases pH video

  14. Exit Slip • When using litmus paper, what color would it turn for an acid? • If something has a pH of 7, what is it considered?

  15. Calculating pH and pOH

  16. Strong Acids vs. Weak Acids

  17. Strong Acids and Strong Bases • Since they ______________ disassociate… …so when HCl is placed in water… 100 molecules of HCl are dissolved in water, __________and __________ions are produced. This comes into play for calculating the pH for strong solutions! completely 100 H+ ions 100 Cl- ions

  18. Measuring the Amount of H+ and OH− Ions in a Solution pH concentration _____ Scale- measures the _____________ of [H+] ions in a solution _____ Scale- measures the concentration of [ ____ ] ions in a solution Formulas pH = − (log [H+]) pOH = −(log [OH−]) [H+] = 10−pH [OH−] = 10−pOH pH + pOH = 14 With the pH scale, we have another way to define acids and bases: Acids have a pH _________7.0 Bases have a pH _________7.0 Neutral pH ___7.0 pOH OH− below above =

  19. [H+] = concentration of hydrogen ions  _______________ (M)! Molarity Before we try calculating pH’s, watch video about background information on pH

  20. Example of Calculating pH a) Calculate the pH of a 0.001 M HCl solution (so 0.001 H+ ions) b) What is the pOH of a solution with a pH of 3? c) What is the concentration of [OH−] ions in the solution? [H+] = 0.001 M pH = − (log 0.001 M) pH = 3 pH + pOH = 14 3+ pOH = 14 pOH = 11 [OH−] = 10−pOH [OH−] = 10−11 M or 1 x 10−11 M pH = − (log [H+]) pOH = −(log [OH−]) [H+] = 10−pH [OH−] = 10−pOH pH + pOH = 14

  21. You Try: a) Calculate the pOH of a NaOH solution that has a pH of 8.50 b) What is the [OH−] of this solution? c) What is the concentration of [H+] ions in the solution? pH + pOH = 14 8.5 + pOH = 14 pOH = 5.5 [OH−] = 10−pOH [OH−] = 10−5.5 Mor 3.16 x 10−6 M [H+] = 10−pH [H+] = 10−8.5 Mor 3.16 x 10−9 M pH = − (log [H+]) pOH = −(log [OH−]) [H+] = 10−pH [OH−] = 10−pOH pH + pOH = 14

  22. Exit Slip Which disassociates to more H+ ions: a strong acid or a weak acid? Calculate the pH of .005 M HCl solution Calculate the pOH of a solution with a pH of 6. pH = − (log [H+]) pOH = −(log [OH−]) [H+] = 10−pH [OH−] = 10−pOH pH + pOH = 14

  23. Acid & Bases Intro to Calculations Answers 1) concentration 2) Concentration of H+ (or Hydronium) Ions 3) Concentration of H+ (or Hydronium) ions 1. a. –log(.005)  2.3 b. –log(2)  -.301 2. a. 5, A b. 12, B c. 7, N d. 10, A 3. a. 10-1.04  0.0912 b. 1013.1  1.26 x 10-13 4. a. –log(.4)  0.398 b. –log(4)  -0.602 *Calculating out a negative pH value does happen when concentrations are above 1.0 M (so for a very concentrated acid)

  24. Recognizing Acids & Bases Neutralization

  25. Recognizing Acids & Bases hydrogen • Acids start with the element: _______________ • Bases generally have the polyatomic ion: _________________ • Another common base: NH3 ammonia! Hydroxide: OH- Hydrogen: H+ hydroxide

  26. Conjugate Acid-Base Pairs Acid base • Conjugate______- substance formed when a _______ gains a [H+] ion. • Conjugate______- substance formed when an ______ loses a [H+] ion. Practice Problems: Label the acid & base on the left side of the reaction and the conjugate acid & conjugate base on the right side. a) HCl + H2O  H3O+ + Cl− ______ ______ ______ ______ b) NH3 + H2O  NH4+ + OH− _____ ______ ______ ______ Base acid acid base C.A. C.B. base acid C.A. C.B.

  27. Neutralization Reactions • Strong acid solutions contain: • Strong base solutions contians: Neutralization reaction: an acid-base reaction that has initial concentrations and volume of reactants equal. Equal H+ and OH-  NEUTRAL solution (pH = 7) H+ ions OH- ions

  28. Neutralization Reactions salt When an acid and base are mixed, the reaction produces a _______ and ___________. • All neutralization reactions are ___________ replacement reactions. water double HX + M(OH)  ______ + ______ MX H2O (“Salt”)

  29. Neutralization (or Acid-Base Reaction) Hydrochloric acid reacts with Sodium hydroxide… HCl (aq) + NaOH (aq)  _________ + __________ NaCl H2O (l) • Salt • an ionic compound produced from a neutralization reaction • composed of equal amount of cations & anions • thus neutral • can be aqueous or depending on solubility may be a precipitate Neutralization Video

  30. Alka-Seltzer Activity Each group needs: 1 small (150 or 250 mL) beaker, 1 alka-seltzer tablet, 1 pH paper • The Indicator is in the front table, add your 10 to 15 drops and then return it to the front! • Vinegar will be at the lab stations. • When you add 3 dropper fullsof vinegar!! *When finished, you may pick up a study guide for the quiz on Wednesday! (will have class time tomorrow to work on the study guide).

  31. Titration A titration is a technique to determine the concentration of a solution (mixes acids and bases) Known concentration is delivered by a buret to an unknown concentration and an indicator is used to determine when neutralization has occurred. The end pointor the equivalence point is the point of neutralization. • H+ ions = OH- ions

  32. Determining the Concentration of an Acid (or Base) by Titration MacidVacid = MbaseVbase A 25 mL solution of HNO3 is neutralized by 18 mL of 1.0 M NaOH standard solution using phenolphthalein as an indicator. What is the concentration of the HNO3 solution? ( ) x ( ) = ( ) x ( ) Macid 25 mL 1.0 M 18 mL Macid = 0.72 M

  33. Determining the Concentration of an Acid (or Base) by Titration You Try How many mL of 2.0 M KOH will it take to neutralize 55 mL of a 0.76 M HCl standard solution? A 0.05 L solution of HNO3 is neutralized by 0.025 L of 1.5 M NaOH standard solution using phenolphthalein as an indicator. What is the concentration of the HNO3 solution?

  34. Exit Slip How many mL of 1.5 M KOH will it take to neutralize 150 mL of a 0.75 M HCl standard solution? What is the pH of a solution has a 1.0M concentration of H+ ions? If you could be a strong acid, weak acid, strong base, weak base, giraffe, kangaroo or the moon, which would you be and why?

  35. Exit Slip Label the acid, base, conjugate acid and conjugate base HF + H2O  H3O+ + F−

  36. Answer Key Practice II 2. False – there is a small amount of H+, pH measures concentration of H ions. If you have a high pH there is a small, if you have a low pH there are more H+ ions 4. A, N, A, B, A, A, B, A, B, A 5)100 mL 6) 0.14 M 7) 0.125 M 8) pH = 10.37, pOH = 3.63, [OH-] = 10-3.63 0.000234 M 9) 25 mL 10) Water and a salt

  37. Semi-answer Key to Acids *  = indicates that it completely breaks apart into the ions (the arrows both ways, indicate that it does not) 4. Hydrofluoric acid, hydrobromic acid, hydroiodic acid, hydrosulfuric acid 1) Phosphoric acid 2) Phosphorous acid 3) Carbonic acid 4) Hydronitric acid 5) Nitrous acid 6) H3P 7) HNO3 8) H2SO3 1) Bariumn Hydroxide 3) Iron (II) Hydroxide 4) NaOH 5) Ca(OH)2 7) A, B, CA, CB 1) Calcium Hydroxide (B) 5) Sulfuric Acid (A) Prediction: HBr + LiOH  LiBr + H2O

  38. Acids & Bases 2

  39. Strong Acids and Strong Bases • Since they ______________ disassociate… …so when HCl is placed in water… 100 molecules of HCl are dissolved in water, __________and __________ions are produced. This comes into play for calculating the pH for strong solutions! completely 100 H+ ions 100 Cl- ions

  40. Find the pH of the following solution… A solution containing 1 mole of hydrochloric acid in 12 L of water pH measures ________________________________. concentration of H+ ions M = mol/L M = 1 mol / 12L M = _____ M HCl • _____ M H+ 0.0833 0.0833 pH = -log( ) 0.0833

  41. Find the pH of the following solution… A solution containing 5 moles of HCl in 10 L of water

  42. Find the pH of the following solution… A solution containing 20 grams of HCl in 10 L of water

  43. Exit Slip Calculate the pH of a solution containing 50 grams of HCl in 2.5 L of water.

  44. Measuring the Amount of H+ and OH− Ions in a Solution pH concentration _____ Scale- measures the _____________ of [H+] ions in a solution _____ Scale- measures the concentration of [ ____ ] ions in a solution Formulas pH = − (log [H+]) pOH = −(log [OH−]) [H+] = 10−pH [OH−] = 10−pOH pH + pOH = 14 With the pH scale, we have another way to define acids and bases: Acids have a pH _________7.0 Bases have a pH _________7.0 Neutral pH ___7.0 pOH OH− below above =

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