Chapter 19 “ Acids, Bases, and Salts ”
Section 19.1 Acid-Base Theories <ul><li>OBJECTIVES: </li></ul><ul><ul><li>Define  the  properties  of acids and bases. </l...
Section 19.1 Acid-Base Theories <ul><li>OBJECTIVES: </li></ul><ul><ul><li>Compare and contrast  acids and bases as  define...
Properties of Acids <ul><li>They taste  sour  (don’t try this at home). </li></ul><ul><li>They can  conduct electricity . ...
Properties of Acids <ul><li>They have a  pH of less than 7  (more on this concept of pH in a later lesson) </li></ul><ul><...
Acids Affect Indicators, by changing their color Blue litmus paper turns red in contact with an acid  (and red paper stays...
Acids have a pH  less   than 7
Acids React with Active Metals Acids react with active metals to form salts and hydrogen gas: HCl (aq)  + Mg (s)   -> MgCl...
Acids React with Carbonates and Bicarbonates HCl  +  NaHCO 3 NaCl + H 2 O + CO 2 Hydrochloric acid + sodium bicarbonate sa...
Effects of  Acid Rain  on Marble (marble is calcium  carbonate ) George Washington: BEFORE acid rain George Washington: AF...
Acids  Neutralize  Bases HCl + NaOH  ->  NaCl + H 2 O - Neutralization reactions ALWAYS produce a salt (which is an  ionic...
Sulfuric Acid  = H 2 SO 4 <ul><li>Highest volume production of  any  chemical in the U.S.  (approximately 60 billion pound...
Nitric Acid  = HNO 3 <ul><li>Used in the production of fertilizers </li></ul><ul><li>Used in the production of explosives ...
Hydrochloric Acid  = HCl <ul><li>Used in the “pickling” of steel </li></ul><ul><li>Used to purify magnesium from sea water...
Phosphoric Acid  = H 3 PO 4 <ul><li>A flavoring agent in sodas (adds “tart”) </li></ul><ul><li>Used in the manufacture of ...
Acetic Acid  = HC 2 H 3 O 2  (also called Ethanoic Acid, CH 3 COOH) <ul><li>Used in the manufacture of plastics </li></ul>...
Properties of Bases   (metallic hydroxides) <ul><li>React with acids  to form water and a salt. </li></ul><ul><li>Taste  b...
Examples of Bases (metallic hydroxides) <ul><li>Sodium hydroxide,  NaOH   ( lye for drain cleaner; soap ) </li></ul><ul><l...
Bases Affect Indicators Red litmus paper turns blue in contact with a base  (and blue paper stays blue). Phenolphthalein t...
Bases have a pH  greater   than 7
Bases Neutralize Acids Milk of Magnesia contains magnesium hydroxide, Mg(OH) 2 , which neutralizes stomach acid, HCl. 2 HC...
Acid-Base Theories
Svante Arrhenius <ul><li>He was a Swedish chemist (1859-1927), and a Nobel prize winner in chemistry (1903) </li></ul><ul>...
Hubert N. Alyea (1903-1996)
1. Arrhenius Definition - 1887 <ul><li>Acids  produce hydrogen ions (H 1+ )  in  aqueous solution   (HCl  ->  H 1+  + Cl 1...
Svante Arrhenius (1859-1927)
Polyprotic Acids? <ul><li>Some compounds have  more than one ionizable hydrogen  to release </li></ul><ul><li>HNO 3  nitri...
Acids <ul><li>Not all compounds that have hydrogen are acids.  Water? </li></ul><ul><li>Also, not all the hydrogen in an a...
Arrhenius examples... <ul><li>Consider HCl = it is an acid! </li></ul><ul><li>What about CH 4  (methane)? </li></ul><ul><l...
Organic Acids  (those with carbon) Organic acids all contain the  carboxyl  group,  (-COOH), sometimes several of them.  C...
2. Brønsted-Lowry - 1923 <ul><li>A broader definition than Arrhenius </li></ul><ul><li>Acid  is hydrogen-ion donor (H +  o...
Johannes Brønsted  Thomas Lowry   (1879-1947)  (1874-1936)   Denmark   England
Why Ammonia is a Base <ul><li>Ammonia can be explained as a base by using Brønsted-Lowry: </li></ul><ul><li>NH 3(aq)  + H ...
Acids and bases come in pairs <ul><li>A “ conjugate base ”  is the remainder of the original acid, after it  donates  it’s...
Acids and bases come in pairs <ul><li>General equation is:  </li></ul><ul><li>HA (aq)  + H 2 O (l)   ↔  H 3 O + (aq)  + A ...
3. Lewis Acids and Bases <ul><li>Gilbert Lewis focused on the donation or acceptance of a pair of electrons during a react...
Gilbert Lewis (1875-1946)
- Page 593
Section 19.2 Hydrogen Ions and Acidity <ul><li>OBJECTIVES: </li></ul><ul><ul><li>Describe  how [H 1+ ] and [OH 1- ] are  r...
Section 19.2 Hydrogen Ions and Acidity <ul><li>OBJECTIVES: </li></ul><ul><ul><li>Classify  a solution as neutral, acidic, ...
Section 19.2 Hydrogen Ions and Acidity <ul><li>OBJECTIVES: </li></ul><ul><ul><li>Convert  hydrogen-ion concentrations  int...
Section 19.2 Hydrogen Ions and Acidity <ul><li>OBJECTIVES: </li></ul><ul><ul><li>Describe  the  purpose  of an acid-base i...
Hydrogen Ions from Water <ul><li>Water ionizes, or falls apart into ions: </li></ul><ul><ul><li>H 2 O  ↔  H 1+  + OH 1- </...
Ion Product Constant <ul><li>H 2 O  ↔  H 1+  + OH 1- </li></ul><ul><li>K w  is  constant  in every aqueous solution:  [H +...
- Page 596
The pH concept – from 0 to 14 <ul><li>pH =  pouvoir hydrogene  (Fr.)      “hydrogen power” </li></ul><ul><li>definition:  ...
 
Calculating pOH <ul><li>pOH = -log [OH - ]  </li></ul><ul><li>[H + ] x [OH - ] = 1 x 10 -14  M 2 </li></ul><ul><li>pH + pO...
pH and Significant Figures <ul><li>For pH calculations, the hydrogen ion concentration is usually expressed in scientific ...
- Page 599
- Page 600
Measuring pH <ul><li>Why measure pH? </li></ul><ul><ul><li>Everyday solutions  we use - everything from swimming pools, so...
How to measure pH with wide-range paper 1. Moisten the pH indicator paper strip with a few drops of solution, by using a s...
Some of the many pH Indicators  and their pH range
Acid-Base Indicators <ul><li>Although useful, there are  limitations   to indicators: </li></ul><ul><ul><li>usually given ...
Acid-Base Indicators <ul><li>A  pH meter  may give more definitive results </li></ul><ul><ul><li>some are  large , others ...
Section 19.3 Strengths of Acids and Bases <ul><li>OBJECTIVES: </li></ul><ul><ul><li>Define   strong acids  and  weak acids...
Section 19.3 Strengths of Acids and Bases <ul><li>OBJECTIVES: </li></ul><ul><ul><li>Describe  how an acid’s strength is  r...
Section 19.3 Strengths of Acids and Bases <ul><li>OBJECTIVES: </li></ul><ul><ul><li>Calculate  an  acid dissociation const...
Section 19.3 Strengths of Acids and Bases <ul><li>OBJECTIVES: </li></ul><ul><ul><li>Order  acids  by strength  according t...
Section 19.3 Strengths of Acids and Bases <ul><li>OBJECTIVES: </li></ul><ul><ul><li>Order  bases  by strength  according t...
Strength <ul><li>Acids and Bases are classified acording to the degree to which they ionize in water: </li></ul><ul><ul><l...
Strength <ul><li>Strong – means it forms  many  ions when dissolved (100 % ionization) </li></ul><ul><li>Mg(OH) 2  is a st...
Strong Acid Dissociation   (makes 100 % ions)
Weak Acid Dissociation (only partially ionizes)
Measuring strength <ul><li>Ionization is reversible: </li></ul><ul><li>HA + H 2 O  ↔  H +  + A -  </li></ul><ul><li>This m...
What about bases? <ul><li>Strong bases dissociate completely. </li></ul><ul><li>MOH + H 2 O  ↔  M +  + OH -   (M = a metal...
Strength vs. Concentration <ul><li>The words  concentrated  and  dilute  tell how much of an acid or base is dissolved in ...
Practice <ul><li>Write the K a  expression for HNO 2 </li></ul><ul><ul><li>Equation: HNO 2   ↔ H 1+  + NO 2 1- </li></ul><...
- Page 610
Section 19.4 Neutralization Reactions <ul><li>OBJECTIVES: </li></ul><ul><ul><li>Define  the  products  of an acid-base rea...
Section 19.4 Neutralization Reactions <ul><li>OBJECTIVES: </li></ul><ul><ul><li>Explain  how acid-base  titration  is used...
Section 19.4 Neutralization Reactions <ul><li>OBJECTIVES: </li></ul><ul><ul><li>Explain  the concept of  equivalence  in n...
Section 19.4 Neutralization Reactions <ul><li>OBJECTIVES: </li></ul><ul><ul><li>Describe  the relationship between  equiva...
Acid-Base Reactions <ul><li>Acid + Base    Water + Salt </li></ul><ul><li>Properties related to every day: </li></ul><ul>...
Acid-Base Reactions <ul><li>Neutralization Reaction  - a reaction in which an acid and a base react in an aqueous solution...
Titration <ul><li>Titration  is the process of adding a known amount of solution of known concentration to determine the c...
- Page 614
Titration <ul><li>The concentration of acid (or base) in solution can be determined by performing a neutralization reactio...
Steps - Neutralization reaction <ul><li>#1. A measured volume of acid of unknown concentration is added to a flask </li></...
Neutralization <ul><li>The solution of known concentration is called the  standard solution </li></ul><ul><ul><li>added by...
Section 19.5 Salts in Solution <ul><li>OBJECTIVES: </li></ul><ul><ul><li>Describe  when a solution of a  salt  is acidic o...
Section 19.5 Salts in Solution <ul><li>OBJECTIVES: </li></ul><ul><ul><li>Demonstrate  with equations how  buffers  resist ...
Salt Hydrolysis <ul><li>A  salt  is an ionic compound that: </li></ul><ul><ul><li>comes from the  anion  of an acid </li><...
Salt Hydrolysis <ul><li>Hydrolyzing salts usually come from: </li></ul><ul><ul><li>a strong acid + a weak base, or </li></...
Salt Hydrolysis <ul><li>To see if the resulting salt is acidic or basic, check the  “parent” acid and base  that formed it...
Buffers <ul><li>Buffers  are solutions in which the pH remains relatively constant, even when small amounts of acid or bas...
Buffers <ul><li>A buffer system is better able to resist changes in pH than pure water </li></ul><ul><li>Since it is a  pa...
Buffers <ul><li>Example: Ethanoic (acetic) acid and sodium ethanoate (also called sodium acetate) </li></ul><ul><li>Exampl...
Buffers <ul><li>The two buffers that are crucial to maintain the pH of human blood are: </li></ul><ul><ul><li>1. carbonic ...
Aspirin (which is a type of acid) sometimes causes stomach upset; thus by adding a “buffer”, it does not cause the acid ir...
End of Chapter 19
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Chemistry - Chp 19 - Acids, Bases, and Salt - PowerPoints

  1. 1. Chapter 19 “ Acids, Bases, and Salts ”
  2. 2. Section 19.1 Acid-Base Theories <ul><li>OBJECTIVES: </li></ul><ul><ul><li>Define the properties of acids and bases. </li></ul></ul>
  3. 3. Section 19.1 Acid-Base Theories <ul><li>OBJECTIVES: </li></ul><ul><ul><li>Compare and contrast acids and bases as defined by the theories of: a) Arrhenius, b) Brønsted-Lowry, and c) Lewis. </li></ul></ul>
  4. 4. Properties of Acids <ul><li>They taste sour (don’t try this at home). </li></ul><ul><li>They can conduct electricity . </li></ul><ul><ul><li>Can be strong or weak electrolytes in aqueous solution </li></ul></ul><ul><li>React with metals to form H 2 gas. </li></ul><ul><li>Change the color of indicators (for example: blue litmus turns to red). </li></ul><ul><li>React with bases (metallic hydroxides) to form water and a salt. </li></ul>
  5. 5. Properties of Acids <ul><li>They have a pH of less than 7 (more on this concept of pH in a later lesson) </li></ul><ul><li>They react with carbonates and bicarbonates to produce a salt, water, and carbon dioxide gas </li></ul><ul><li>How do you know if a chemical is an acid? </li></ul><ul><ul><li>It usually starts with Hydrogen. </li></ul></ul><ul><ul><li>H Cl, H 2 SO 4 , H NO 3 , etc. (but not water!) </li></ul></ul>
  6. 6. Acids Affect Indicators, by changing their color Blue litmus paper turns red in contact with an acid (and red paper stays red).
  7. 7. Acids have a pH less than 7
  8. 8. Acids React with Active Metals Acids react with active metals to form salts and hydrogen gas: HCl (aq) + Mg (s) -> MgCl 2(aq) + H 2(g) This is a single-replacement reaction
  9. 9. Acids React with Carbonates and Bicarbonates HCl + NaHCO 3 NaCl + H 2 O + CO 2 Hydrochloric acid + sodium bicarbonate salt + water + carbon dioxide An old-time home remedy for relieving an upset stomach
  10. 10. Effects of Acid Rain on Marble (marble is calcium carbonate ) George Washington: BEFORE acid rain George Washington: AFTER acid rain
  11. 11. Acids Neutralize Bases HCl + NaOH -> NaCl + H 2 O - Neutralization reactions ALWAYS produce a salt (which is an ionic compound ) and water. -Of course, it takes the right proportion of acid and base to produce a neutral salt
  12. 12. Sulfuric Acid = H 2 SO 4 <ul><li>Highest volume production of any chemical in the U.S. (approximately 60 billion pounds/year) </li></ul><ul><li>Used in the production of paper </li></ul><ul><li>Used in production of fertilizers </li></ul><ul><li>Used in petroleum refining; auto batteries </li></ul>
  13. 13. Nitric Acid = HNO 3 <ul><li>Used in the production of fertilizers </li></ul><ul><li>Used in the production of explosives </li></ul><ul><li>Nitric acid is a volatile acid – its reactive components evaporate easily </li></ul><ul><li>Stains proteins yellow (including skin!) </li></ul>
  14. 14. Hydrochloric Acid = HCl <ul><li>Used in the “pickling” of steel </li></ul><ul><li>Used to purify magnesium from sea water </li></ul><ul><li>Part of gastric juice, it aids in the digestion of proteins </li></ul><ul><li>Sold commercially as Muriatic acid </li></ul>
  15. 15. Phosphoric Acid = H 3 PO 4 <ul><li>A flavoring agent in sodas (adds “tart”) </li></ul><ul><li>Used in the manufacture of detergents </li></ul><ul><li>Used in the manufacture of fertilizers </li></ul><ul><li>Not a common laboratory reagent </li></ul>
  16. 16. Acetic Acid = HC 2 H 3 O 2 (also called Ethanoic Acid, CH 3 COOH) <ul><li>Used in the manufacture of plastics </li></ul><ul><li>Used in making pharmaceuticals </li></ul><ul><li>Acetic acid is the acid that is present in household vinegar </li></ul>
  17. 17. Properties of Bases (metallic hydroxides) <ul><li>React with acids to form water and a salt. </li></ul><ul><li>Taste bitter . </li></ul><ul><li>Feel slippery (don’t try this either). </li></ul><ul><li>Can be strong or weak electrolytes in aqueous solution </li></ul><ul><li>Change the color of indicators (red litmus turns blue). </li></ul>
  18. 18. Examples of Bases (metallic hydroxides) <ul><li>Sodium hydroxide, NaOH ( lye for drain cleaner; soap ) </li></ul><ul><li>Potassium hydroxide, KOH ( alkaline batteries ) </li></ul><ul><li>Magnesium hydroxide, Mg(OH) 2 ( Milk of Magnesia ) </li></ul><ul><li>Calcium hydroxide, Ca(OH) 2 ( lime ; masonry ) </li></ul>
  19. 19. Bases Affect Indicators Red litmus paper turns blue in contact with a base (and blue paper stays blue). Phenolphthalein turns purple in a base.
  20. 20. Bases have a pH greater than 7
  21. 21. Bases Neutralize Acids Milk of Magnesia contains magnesium hydroxide, Mg(OH) 2 , which neutralizes stomach acid, HCl. 2 HCl + Mg(OH) 2 MgCl 2 + 2 H 2 O Magnesium salts can cause diarrhea (thus they are used as a laxative) and may also cause kidney stones.
  22. 22. Acid-Base Theories
  23. 23. Svante Arrhenius <ul><li>He was a Swedish chemist (1859-1927), and a Nobel prize winner in chemistry (1903) </li></ul><ul><li>one of the first chemists to explain the chemical theory of the behavior of acids and bases </li></ul><ul><li>Dr. Hubert Alyea (professor emeritus at Princeton University) was the last graduate student of Arrhenius. </li></ul>
  24. 24. Hubert N. Alyea (1903-1996)
  25. 25. 1. Arrhenius Definition - 1887 <ul><li>Acids produce hydrogen ions (H 1+ ) in aqueous solution (HCl -> H 1+ + Cl 1- ) </li></ul><ul><li>Bases produce hydroxide ions (OH 1- ) when dissolved in water . </li></ul><ul><ul><li>(NaOH -> Na 1+ + OH 1- ) </li></ul></ul><ul><li>Limited to aqueous solutions . </li></ul><ul><li>Only one kind of base (hydroxides) </li></ul><ul><li>NH 3 (ammonia) could not be an Arrhenius base: no OH 1- produced. </li></ul>
  26. 26. Svante Arrhenius (1859-1927)
  27. 27. Polyprotic Acids? <ul><li>Some compounds have more than one ionizable hydrogen to release </li></ul><ul><li>HNO 3 nitric acid - mono protic </li></ul><ul><li>H 2 SO 4 sulfuric acid - di protic - 2 H + </li></ul><ul><li>H 3 PO 4 phosphoric acid - tri protic - 3 H + </li></ul><ul><li>Having more than one ionizable hydrogen does not mean stronger! </li></ul>
  28. 28. Acids <ul><li>Not all compounds that have hydrogen are acids. Water? </li></ul><ul><li>Also, not all the hydrogen in an acid may be released as ions </li></ul><ul><ul><li>only those that have very polar bonds are ionizable - this is when the hydrogen is joined to a very electronegative element </li></ul></ul>
  29. 29. Arrhenius examples... <ul><li>Consider HCl = it is an acid! </li></ul><ul><li>What about CH 4 (methane)? </li></ul><ul><li>CH 3 COOH (ethanoic acid, also called acetic acid) - it has 4 hydrogens just like methane does…? </li></ul><ul><li>Table 19.2, p. 589 for bases, which are metallic hydroxides </li></ul>
  30. 30. Organic Acids (those with carbon) Organic acids all contain the carboxyl group, (-COOH), sometimes several of them. CH 3 COOH – of the 4 hydrogen, only 1 ionizable The carboxyl group is a poor proton donor, so ALL organic acids are weak acids . (due to being bonded to the highly electronegative Oxygen )
  31. 31. 2. Brønsted-Lowry - 1923 <ul><li>A broader definition than Arrhenius </li></ul><ul><li>Acid is hydrogen-ion donor (H + or proton); base is hydrogen-ion acceptor. </li></ul><ul><li>Acids and bases always come in pairs. </li></ul><ul><li>HCl is an acid. </li></ul><ul><ul><li>When it dissolves in water, it gives it’s proton to water. </li></ul></ul><ul><li>HCl (g) + H 2 O (l) ↔ H 3 O + (aq) + Cl - (aq) </li></ul><ul><li>Water is a base; makes hydronium ion. </li></ul>
  32. 32. Johannes Brønsted Thomas Lowry (1879-1947) (1874-1936) Denmark England
  33. 33. Why Ammonia is a Base <ul><li>Ammonia can be explained as a base by using Brønsted-Lowry: </li></ul><ul><li>NH 3(aq) + H 2 O (l) ↔ NH 4 1+ (aq) + OH 1- (aq) </li></ul><ul><li>Ammonia is the hydrogen ion acceptor ( base ), and water is the hydrogen ion donor ( acid ). </li></ul><ul><li>This causes the OH 1- concentration to be greater than in pure water, and the ammonia solution is basic </li></ul>
  34. 34. Acids and bases come in pairs <ul><li>A “ conjugate base ” is the remainder of the original acid, after it donates it’s hydrogen ion </li></ul><ul><li>A “ conjugate acid ” is the particle formed when the original base gains a hydrogen ion </li></ul><ul><li>Thus, a conjugate acid-base pair is related by the loss or gain of a single hydrogen ion . </li></ul><ul><li>Chemical Indicators ? They are weak acids or bases that have a different color from their original acid and base </li></ul>
  35. 35. Acids and bases come in pairs <ul><li>General equation is: </li></ul><ul><li>HA (aq) + H 2 O (l) ↔ H 3 O + (aq) + A - (aq) </li></ul><ul><li>Acid + Base ↔ Conjugate acid + Conjugate base </li></ul><ul><li>NH 3 + H 2 O ↔ NH 4 1+ + OH 1- </li></ul><ul><li>base acid c.a. c.b. </li></ul><ul><li>HCl + H 2 O ↔ H 3 O 1+ + Cl 1- </li></ul><ul><li>acid base c.a. c.b. </li></ul><ul><li>Amphoteric – a substance that can act as both an acid and base- as water shows </li></ul>
  36. 36. 3. Lewis Acids and Bases <ul><li>Gilbert Lewis focused on the donation or acceptance of a pair of electrons during a reaction </li></ul><ul><li>Lewis Acid - electron pair acceptor </li></ul><ul><li>Lewis Base - electron pair donor </li></ul><ul><li>Most general of all 3 definitions; acids don’t even need hydrogen! </li></ul><ul><li>Summary : Table 19.4, page 592 </li></ul>
  37. 37. Gilbert Lewis (1875-1946)
  38. 38. - Page 593
  39. 39. Section 19.2 Hydrogen Ions and Acidity <ul><li>OBJECTIVES: </li></ul><ul><ul><li>Describe how [H 1+ ] and [OH 1- ] are related in an aqueous solution. </li></ul></ul>
  40. 40. Section 19.2 Hydrogen Ions and Acidity <ul><li>OBJECTIVES: </li></ul><ul><ul><li>Classify a solution as neutral, acidic, or basic given the hydrogen-ion or hydroxide-ion concentration. </li></ul></ul>
  41. 41. Section 19.2 Hydrogen Ions and Acidity <ul><li>OBJECTIVES: </li></ul><ul><ul><li>Convert hydrogen-ion concentrations into pH values and hydroxide-ion concentrations into pOH values. </li></ul></ul>
  42. 42. Section 19.2 Hydrogen Ions and Acidity <ul><li>OBJECTIVES: </li></ul><ul><ul><li>Describe the purpose of an acid-base indicator. </li></ul></ul>
  43. 43. Hydrogen Ions from Water <ul><li>Water ionizes, or falls apart into ions: </li></ul><ul><ul><li>H 2 O ↔ H 1+ + OH 1- </li></ul></ul><ul><li>Called the “ self ionization ” of water </li></ul><ul><li>Occurs to a very small extent : </li></ul><ul><ul><li>[H 1+ ] = [OH 1- ] = 1 x 10 -7 M </li></ul></ul><ul><li>Since they are equal, a neutral solution results from water </li></ul><ul><li>K w = [H 1+ ] x [OH 1- ] = 1 x 10 -14 M 2 </li></ul><ul><li>K w is called the “ ion product constant ” for water </li></ul>
  44. 44. Ion Product Constant <ul><li>H 2 O ↔ H 1+ + OH 1- </li></ul><ul><li>K w is constant in every aqueous solution: [H + ] x [OH - ] = 1 x 10 -14 M 2 </li></ul><ul><li>If [H + ] > 10 -7 then [OH - ] < 10 -7 </li></ul><ul><li>If [H + ] < 10 -7 then [OH - ] > 10 -7 </li></ul><ul><li>If we know one, other can be determined </li></ul><ul><li>If [H + ] > 10 -7 , it is acidic and [OH - ] < 10 -7 </li></ul><ul><li>If [H + ] < 10 -7 , it is basic and [OH - ] > 10 -7 </li></ul><ul><ul><li>Basic solutions also called “alkaline” </li></ul></ul>
  45. 45. - Page 596
  46. 46. The pH concept – from 0 to 14 <ul><li>pH = pouvoir hydrogene (Fr.) “hydrogen power” </li></ul><ul><li>definition: pH = -log[H + ] </li></ul><ul><li>in neutral pH = -log(1 x 10 -7 ) = 7 </li></ul><ul><li>in acidic solution [H + ] > 10 -7 </li></ul><ul><li>pH < -log(10 -7 ) </li></ul><ul><ul><li>pH < 7 (from 0 to 7 is the acid range) </li></ul></ul><ul><ul><li>in base , pH > 7 (7 to 14 is base range) </li></ul></ul>
  47. 48. Calculating pOH <ul><li>pOH = -log [OH - ] </li></ul><ul><li>[H + ] x [OH - ] = 1 x 10 -14 M 2 </li></ul><ul><li>pH + pOH = 14 </li></ul><ul><li>Thus, a solution with a pOH less than 7 is basic; with a pOH greater than 7 is an acid </li></ul><ul><li>Not greatly used like pH is. </li></ul>
  48. 49. pH and Significant Figures <ul><li>For pH calculations, the hydrogen ion concentration is usually expressed in scientific notation </li></ul><ul><li>[H 1+ ] = 0.0010 M = 1.0 x 10 -3 M, and 0.00 10 has 2 significant figures </li></ul><ul><li>the pH = 3. 00 , with the two numbers to the right of the decimal corresponding to the two significant figures </li></ul>
  49. 50. - Page 599
  50. 51. - Page 600
  51. 52. Measuring pH <ul><li>Why measure pH? </li></ul><ul><ul><li>Everyday solutions we use - everything from swimming pools, soil conditions for plants, medical diagnosis, soaps and shampoos, etc. </li></ul></ul><ul><li>Sometimes we can use indicators , other times we might need a pH meter </li></ul>
  52. 53. How to measure pH with wide-range paper 1. Moisten the pH indicator paper strip with a few drops of solution, by using a stirring rod. 2.Compare the color to the chart on the vial – then read the pH value.
  53. 54. Some of the many pH Indicators and their pH range
  54. 55. Acid-Base Indicators <ul><li>Although useful, there are limitations to indicators: </li></ul><ul><ul><li>usually given for a certain temperature (25 o C), thus may change at different temperatures </li></ul></ul><ul><ul><li>what if the solution already has a color , like paint? </li></ul></ul><ul><ul><li>the ability of the human eye to distinguish colors is limited </li></ul></ul>
  55. 56. Acid-Base Indicators <ul><li>A pH meter may give more definitive results </li></ul><ul><ul><li>some are large , others portable </li></ul></ul><ul><ul><li>works by measuring the voltage between two electrodes; typically accurate to within 0.01 pH unit of the true pH </li></ul></ul><ul><ul><li>Instruments need to be calibrated </li></ul></ul><ul><ul><li>Fig. 19.15, p.603 </li></ul></ul>
  56. 57. Section 19.3 Strengths of Acids and Bases <ul><li>OBJECTIVES: </li></ul><ul><ul><li>Define strong acids and weak acids . </li></ul></ul>
  57. 58. Section 19.3 Strengths of Acids and Bases <ul><li>OBJECTIVES: </li></ul><ul><ul><li>Describe how an acid’s strength is related to the value of its acid dissociation constant. </li></ul></ul>
  58. 59. Section 19.3 Strengths of Acids and Bases <ul><li>OBJECTIVES: </li></ul><ul><ul><li>Calculate an acid dissociation constant (K a ) from concentration and pH measurements. </li></ul></ul>
  59. 60. Section 19.3 Strengths of Acids and Bases <ul><li>OBJECTIVES: </li></ul><ul><ul><li>Order acids by strength according to their acid dissociation constants (K a ). </li></ul></ul>
  60. 61. Section 19.3 Strengths of Acids and Bases <ul><li>OBJECTIVES: </li></ul><ul><ul><li>Order bases by strength according to their base dissociation constants (K b ). </li></ul></ul>
  61. 62. Strength <ul><li>Acids and Bases are classified acording to the degree to which they ionize in water: </li></ul><ul><ul><li>Strong are completely ionized in aqueous solution; this means they ionize 100 % </li></ul></ul><ul><ul><li>Weak ionize only slightly in aqueous solution </li></ul></ul><ul><li>Strength is very different from Concentration </li></ul>
  62. 63. Strength <ul><li>Strong – means it forms many ions when dissolved (100 % ionization) </li></ul><ul><li>Mg(OH) 2 is a strong base- it falls completely apart (nearly 100% when dissolved). </li></ul><ul><ul><li>But, not much dissolves- so it is not concentrated </li></ul></ul>
  63. 64. Strong Acid Dissociation (makes 100 % ions)
  64. 65. Weak Acid Dissociation (only partially ionizes)
  65. 66. Measuring strength <ul><li>Ionization is reversible: </li></ul><ul><li>HA + H 2 O ↔ H + + A - </li></ul><ul><li>This makes an equilibrium </li></ul><ul><li>Acid dissociation constant = K a </li></ul><ul><li>K a = [H + ][A - ] [HA] </li></ul><ul><li>Stronger acid = more products (ions), thus a larger K a (Table 19.7, page 607) </li></ul>(Note that water is NOT shown, because its concentration is constant, and built into K a ) (Note that the arrow goes both directions.)
  66. 67. What about bases? <ul><li>Strong bases dissociate completely. </li></ul><ul><li>MOH + H 2 O ↔ M + + OH - (M = a metal) </li></ul><ul><li>Base dissociation constant = K b </li></ul><ul><li>K b = [M + ][OH - ] [MOH] </li></ul><ul><li>Stronger base = more dissociated ions are produced, thus a larger K b . </li></ul>
  67. 68. Strength vs. Concentration <ul><li>The words concentrated and dilute tell how much of an acid or base is dissolved in solution - refers to the number of moles of acid or base in a given volume </li></ul><ul><li>The words strong and weak refer to the extent of ionization of an acid or base </li></ul><ul><li>Is a concentrated, weak acid possible? </li></ul>
  68. 69. Practice <ul><li>Write the K a expression for HNO 2 </li></ul><ul><ul><li>Equation: HNO 2 ↔ H 1+ + NO 2 1- </li></ul></ul><ul><ul><li>K a = [H 1 + ] x [NO 2 1 - ] [ HNO 2 ] </li></ul></ul><ul><li>Write the K b expression for NH 3 (as NH 4 OH) </li></ul>
  69. 70. - Page 610
  70. 71. Section 19.4 Neutralization Reactions <ul><li>OBJECTIVES: </li></ul><ul><ul><li>Define the products of an acid-base reaction. </li></ul></ul>
  71. 72. Section 19.4 Neutralization Reactions <ul><li>OBJECTIVES: </li></ul><ul><ul><li>Explain how acid-base titration is used to calculate the concentration of an acid or a base. </li></ul></ul>
  72. 73. Section 19.4 Neutralization Reactions <ul><li>OBJECTIVES: </li></ul><ul><ul><li>Explain the concept of equivalence in neutralization reactions. </li></ul></ul>
  73. 74. Section 19.4 Neutralization Reactions <ul><li>OBJECTIVES: </li></ul><ul><ul><li>Describe the relationship between equivalence point and the end point of a titration. </li></ul></ul>
  74. 75. Acid-Base Reactions <ul><li>Acid + Base  Water + Salt </li></ul><ul><li>Properties related to every day: </li></ul><ul><ul><li>antacids depend on neutralization </li></ul></ul><ul><ul><li>farmers adjust the soil pH </li></ul></ul><ul><ul><li>formation of cave stalactites </li></ul></ul><ul><ul><li>human body kidney stones from insoluble salts </li></ul></ul>
  75. 76. Acid-Base Reactions <ul><li>Neutralization Reaction - a reaction in which an acid and a base react in an aqueous solution to produce a salt and water: </li></ul><ul><li>HCl (aq) + NaOH (aq)  NaCl (aq) + H 2 O (l) </li></ul><ul><li>H 2 SO 4(aq) + 2KOH (aq)  K 2 SO 4(aq) + 2H 2 O (l) </li></ul><ul><ul><li>Table 19.9, page 613 lists some salts </li></ul></ul>
  76. 77. Titration <ul><li>Titration is the process of adding a known amount of solution of known concentration to determine the concentration of another solution </li></ul><ul><li>Remember? - a balanced equation is a mole ratio </li></ul><ul><li>The equivalence point is when the moles of hydrogen ions is equal to the moles of hydroxide ions (= neutralized!) </li></ul>
  77. 78. - Page 614
  78. 79. Titration <ul><li>The concentration of acid (or base) in solution can be determined by performing a neutralization reaction </li></ul><ul><ul><li>An indicator is used to show when neutralization has occurred </li></ul></ul><ul><ul><li>Often we use phenolphthalein - because it is colorless in neutral and acid; turns pink in base </li></ul></ul>
  79. 80. Steps - Neutralization reaction <ul><li>#1. A measured volume of acid of unknown concentration is added to a flask </li></ul><ul><li>#2. Several drops of indicator added </li></ul><ul><li>#3. A base of known concentration is slowly added, until the indicator changes color; measure the volume </li></ul><ul><ul><li>Figure 19.22, page 615 </li></ul></ul>
  80. 81. Neutralization <ul><li>The solution of known concentration is called the standard solution </li></ul><ul><ul><li>added by using a buret </li></ul></ul><ul><li>Continue adding until the indicator changes color </li></ul><ul><ul><li>called the “ end point ” of the titration </li></ul></ul><ul><ul><li>Sample Problem 19.7, page 616 </li></ul></ul>
  81. 82. Section 19.5 Salts in Solution <ul><li>OBJECTIVES: </li></ul><ul><ul><li>Describe when a solution of a salt is acidic or basic. </li></ul></ul>
  82. 83. Section 19.5 Salts in Solution <ul><li>OBJECTIVES: </li></ul><ul><ul><li>Demonstrate with equations how buffers resist changes in pH. </li></ul></ul>
  83. 84. Salt Hydrolysis <ul><li>A salt is an ionic compound that: </li></ul><ul><ul><li>comes from the anion of an acid </li></ul></ul><ul><ul><li>comes from the cation of a base </li></ul></ul><ul><ul><li>is formed from a neutralization reaction </li></ul></ul><ul><ul><li>some neutral; others acidic or basic </li></ul></ul><ul><li>“ Salt hydrolysis ” - a salt that reacts with water to produce an acid or base </li></ul>
  84. 85. Salt Hydrolysis <ul><li>Hydrolyzing salts usually come from: </li></ul><ul><ul><li>a strong acid + a weak base, or </li></ul></ul><ul><ul><li>a weak acid + a strong base </li></ul></ul><ul><li>Strong refers to the degree of ionization </li></ul><ul><ul><li>A strong Acid + a strong Base = Neutral Salt </li></ul></ul><ul><li>How do you know if it’s strong? </li></ul><ul><ul><li>Refer to the handout provided (downloadable from my web site) </li></ul></ul>
  85. 86. Salt Hydrolysis <ul><li>To see if the resulting salt is acidic or basic, check the “parent” acid and base that formed it. Practice on these: </li></ul><ul><ul><li>HCl + NaOH  </li></ul></ul><ul><ul><li>H 2 SO 4 + NH 4 OH  </li></ul></ul><ul><ul><li>CH 3 COOH + KOH  </li></ul></ul>NaCl, a neutral salt (NH 4 ) 2 SO 4 , acidic salt CH 3 COOK, basic salt
  86. 87. Buffers <ul><li>Buffers are solutions in which the pH remains relatively constant, even when small amounts of acid or base are added </li></ul><ul><ul><li>made from a pair of chemicals : a weak acid and one of it’s salts ; or a weak base and one of it’s salts </li></ul></ul>
  87. 88. Buffers <ul><li>A buffer system is better able to resist changes in pH than pure water </li></ul><ul><li>Since it is a pair of chemicals: </li></ul><ul><ul><li>one chemical neutralizes any acid added, while the other chemical would neutralize any additional base </li></ul></ul><ul><ul><li>AND, they produce each other in the process!!! </li></ul></ul>
  88. 89. Buffers <ul><li>Example: Ethanoic (acetic) acid and sodium ethanoate (also called sodium acetate) </li></ul><ul><li>Examples on page 621 of these </li></ul><ul><li>The buffer capacity is the amount of acid or base that can be added before a significant change in pH </li></ul>
  89. 90. Buffers <ul><li>The two buffers that are crucial to maintain the pH of human blood are: </li></ul><ul><ul><li>1. carbonic acid (H 2 CO 3 ) & hydrogen carbonate (HCO 3 1- ) </li></ul></ul><ul><ul><li>2. dihydrogen phosphate (H 2 PO 4 1- ) & monohydrogen phoshate (HPO 4 2- ) </li></ul></ul><ul><ul><li>Table 19.10, page 621 has some important buffer systems </li></ul></ul><ul><ul><li>Conceptual Problem 19.2, p. 622 </li></ul></ul>
  90. 91. Aspirin (which is a type of acid) sometimes causes stomach upset; thus by adding a “buffer”, it does not cause the acid irritation. Bufferin is one brand of a buffered aspirin that is sold in stores. What about the cost compared to plain aspirin?
  91. 92. End of Chapter 19
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