Chapter 10. Acids and Bases

Transcription

1 Chapter 10 Acids and Bases 1

2 Properties of Aqueous Solutions of Acids and Bases Aqueous acidic solutions have the following properties: 1. They have a sour taste.. They change the colors of many indicators. Acids turn blue litmus to red.. They react with metals to generate hydrogen, H (g). 4. Acidic aqueous solutions conduct electricity.

3 Properties of Aqueous Solutions of Acids and Bases Aqueous basic solutions have the following properties: 1. They have a bitter taste.. They have a slippery feeling.. They change the colors of many indicators Bases turn red litmus to blue. Bases turn bromothymol blue from yellow to blue. 4. They react with acids to form salts and water. 5. Aqueous basic solutions conduct electricity.

4 Properties of Aqueous Solutions of Acids and Bases 4

5 The Arrhenius Theory Svante Augustus Arrhenius first presented this theory of acids and bases in Acids are substances that contain hydrogen and produces H in aqueous solutions. H is a proton. Protons (H ) generated in acid-base reactions and dissociations are not present in aqueous solution by themselves. Protons are ALWAYS surrounded by several water molecules. How many varies from solution to solution. H (aq) is really H(H O) n Chemists normally write the hydrated hydrogen ion as H O and call it the hydronium ion. 5

6 The Arrhenius Theory Two examples of substances that behave as Arrhenius acids: HCl HCO (aq) H H (aq) O ( ) H O H O Cl H O ( ) ( aq ) ( aq ) ( aq ) - HCO (aq) 6

7 The Arrhenius Theory Bases are substances that contain the hydroxyl, OH, group and produce hydroxide ions, OH -, in aqueous solutions. Two examples of substances that behave as Arrhenius bases: NaOH NH (g) H Na O OH ( aq ) ( aq ) NH 4 - OH ( aq ) ( aq ) 7

8 Bases 8

9 Naming Acids Acids are compounds consisting of hydrogen and a nonmetal. Compounds are gases at room temperature and pressure. Nomenclature for compounds is hydrogen (stem)ide. Become aqueous acids when dissolved in water, NEW NAME! hydro stemic acid Hydrogen and an anion HCl hydrochloric acid stemic acid Polyatomics with ate Nitric Acid HNO stemous acid Polyatomics with ite Nitrous Acid- HNO 9

10 Naming Some Inorganic Compounds 10

11 Naming Bases Most bases are compounds consisting of hydroxide and a metal. Compounds are solids at room temperature and pressure. In water dissociate to cation of metal and hydroxide No special namng, follow old rules NaOH Ca(OH) Al(OH) 11

12 Some bases in over the counter meds 1

13 The Arrhenius Theory Strong acids are acidic substances that ionize 100% in water. List of aqueous strong acids: HCl, HBr, HI, H SO 4, HNO, HClO 4, HClO Strong bases are basic substances that ionize 100% in water. List of aqueous strong bases: LiOH, NaOH, KOH, RbOH, CsOH, Ca(OH), Sr(OH), Ba(OH) 1

14 Strong Acids vs. Weak Acids 14

15 The Arrhenius Theory Neutralization reactions are the combination of H (or H O ) with OH - to form H O. Example strong acid-strong base reaction, HCl NaOH NaCl H aq O ( ( ) ( aq) ( aq) ) 15

16 The BrØnsted-Lowry Theory J.N. BrØnsted and T.M. Lowry developed this more general acid-base theory in 19. An acid is a proton donor (H ). A base is a proton acceptor. Two examples to illustrate this concept. NH H O NH 4 OH - base acid HBr H O H O Br - acid base 16

17 The BrØnsted-Lowry Theory Acid-base reactions are the transfer of a proton from an acid to a base. HCl NH NH 4 You determine the acid and base for this reaction. Cl - 17

18 The BrØnsted-Lowry Theory An important part of BrØnsted-Lowry acid-base theory is the idea of conjugate acid-base pairs. Two species that differ by a proton are called acid-base conjugate pairs. For example we can use this reaction: HNO H O H O NO - 1. Identify the reactant acid and base.. Find the species that differs from the acid by a proton, that is the conjugate base. 18

19 The BrØnsted-Lowry Theory. Find the species that differs from the base by a proton, that is the conjugate acid. HNO is the acid, conjugate base is NO - H O is the base, conjugate acid is H O 19

20 The BrØnsted-Lowry Theory Conjugate acid-base pairs are species that differ by a proton. Some examples: 0

21 The BrØnsted-Lowry Theory Standard format for writing conjugate acid-base pairs. - HF H O H O F acid base acid base The subscript 1's indicate the1 H HF - acid 1 O - base F H O - base acid The subscript 's indicate the st nd pair. pair. 1

22 The BrØnsted-Lowry Theory An important concept in BrØnsted-Lowry theory involves the relative strengths of acid-base pairs. Weak acids have strong conjugate bases. Weak bases have strong conjugate acids. The weaker the acid or base, the stronger the conjugate partner. The reason why a weak acid is weak is because the conjugate base is so strong it reforms the original acid. Similarly for weak bases.

23 The BrØnsted-Lowry Theory NH H O NH OH 4 Since NH is a weak base, NH 4 must be a strong acid. NH 4 gives up H to reform NH. Compare that to NaOH Na (aq) OH - (aq) Na must be a weak acid or it would recombine to form NaOH Remember NaOH ionizes 100%. NaOH is a strong base. -

24 Conjugate Acids and Bases 4

25 The BrØnsted-Lowry Theory Amines are weak bases that behave similarly to ammonia. The functional group for amines is an -NH group attached to other organic groups. NH H O NH OH 4 CH NH H O CH NH - OH - 5

26 The Autoionization of Water Water can be either an acid or base in Bronsted-Lowry theory. Consequently, water can react with itself. This reaction is called autoionization. One water molecule acts as a base and the other as an acid. - H O H O H O OH base 1 acid acid 1 base 6

27 The Autoionization of Water Water does not do this extensively. [H O ] [OH - ] 1.0 x 10-7 M Autoionization is the basis of the ph scale 7

28 The Autoionization of Water We can write the autoionization of water as a dissociation reaction H O H O H O OH - ( ) ( ) (aq) (aq) K [ H O ][ OH ] c 8

29 The Autoionization of Water Experimental measurements have determined that the concentration of each ion is 1.0 x 10-7 M at 5 o C. Note that this is at 5 o C, not every temperature! We can determine the value of K c from this information. K [ H O ][ OH ] c ( 1.0 x 10-7 )( 1.0 x 10-7 ) 1.0 x

30 The Autoionization of Water This particular equilibrium constant is called the ionproduct for water and given the symbol K w. [ ][ ] K H O OH w 1.0 x

31 The Autoionization of Water Example 10-1: Calculate the concentrations of H O and OH - in M HCl. The [ H O ] HCl 0.050M Thus and K H the w O 0.050M [ H O ] H O Cl 0.050M 0.050M. - will allow us to calculate[oh ]. 1

32 The Autoionization of Water Use the [H O ] and K w to determine the [OH - ]. [ ][ ] H O OH You do it! [ ] OH [ ] H O 5.0 [ ] 1 OH.0 10 M

33 The ph and poh scales A convenient way to express the acidity and basicity of a solution is the ph and poh scales. The ph of an aqueous solution is defined as: ph -log[ H O ] [ - ] poh -log OH

34 The ph and poh scales 4

35 The ph and poh scales ph poh

36 The ph and poh scales 6

37 The ph and poh scales If either the [H O ] or [OH - ] is known, the ph and poh can be calculated. Example 10-: Calculate the ph of a solution in which the [H O ] 0.00 M. ph ph ph -log log 1.5 [ ] H O ( )

38 The ph and poh scales Example 10-: The ph of a solution is What is the concentration of H O? You do it! log[h O [H O [H O ph ] ] 10 ] -log[h O log[h O ] ] M 8

39 The ph and poh scales The usual range for the ph scale is 0 to 14. [ H O ] 1.0 to [ H O ] M ph 0 to ph And for poh the scale is also 0 to 14 but inverted from ph. ph 0 has a poh 14 and ph 14 has a poh 0. [ ] [ ] OH M up to OH poh poh M 1.0M 0 9

40 The ph and poh scales Example 10-4: Calculate the [H O ], ph, [OH - ], and poh for a 0.00 M HNO solution. Is HNO a weak or strong acid? What is the [H O ]? HNO 0.00M [ H O ] ph ph H -log % O H O.0 10 M (.0 10 M ) 0.00M NO M 40

41 The ph and poh scales Example 10-5: Calculate the [H O], ph, [OH - ], and poh for a 0.00 M HNO solution. K w [ OH ] poh [ H O ][ OH ] [ ] H O.0 10 [ ] log M 41

42 Dilution of Solutions To dilute a solution, add solvent to a concentrated solution. One method to make tea less sweet. How fountain drinks are made from syrup. The number of moles of solute in the two solutions remains constant. The relationship M 1 V 1 M V is used for dilutions. 4

43 Dilution of Solutions 4

44 Dilution of Solutions Example 10-6: If 10.0 ml of 1.0 M HCl is added to enough water to give 100. ml of solution, what is the concentration of the solution? 1.0 M M M V ml 1 M M V ml 1.0 M ml 1.0 M ml 44

45 Dilution of Solutions Example 10-7: What volume of 18.0 M sulfuric acid is required to make.50 L of a.40 M sulfuric acid solution? You do it! 45

46 Dilution of Solutions Example 10-8: What volume of 18.0 M sulfuric acid is required to make.50 L of a.40 M sulfuric acid solution? M 1 V V V M M V M 1 V.50 L.40 M 18.0 M 0. L or ml 46

47 Buffer Solutions 1. Buffers are solutions made of weak acids plus a soluble ionic salt of the weak acid One example of this type of buffer system is: The weak acid - acetic acid CH COOH The soluble ionic salt - sodium acetate NaCH COO The weak acid reacts with bases. - CH COOH CH COO Na CH COO 100% H Na CH COO The salt anion (a base) reacts - with acids. 47

48 Buffer Solutions 48

49 Buffer Solutions 49

50 Buffer Solutions in Medicine 50

51 Buffer Solutions The general expression for the ionization of a weak monoprotic acid is: HA H A The generalized ionization constant expression for a weak acid is: K a [ H ][ A ] [ HA] 51

52 Buffer Equation ph pka log [ salt] [ acid] 5

53 Using Solutions in Chemical Reactions Titrations are a method of determining the concentration of an unknown solutions from the known concentration of a solution and solution reaction stoichiometry. Requires special lab glassware Buret, pipet, and flasks Must have an an indicator also 5

54 Titrations Acid-base Titration Terminology 1. Titration A method of determining the concentration of one solution by reacting it with a solution of known concentration.. Primary standard A chemical compound which can be used to accurately determine the concentration of another solution. Examples include KHP and sodium carbonate.. Standard solution A solution whose concentration has been determined using a primary standard. 4. Standardization The process in which the concentration of a solution is determined by accurately measuring the volume of the solution required to react with a known amount of a primary standard. 54

55 Titrations Acid-base Titration Terminology 5. Indicator A substance that exists in different forms with different colors depending on the concentration of the H in solution. Examples are phenolphthalein and bromothymol blue. 6. Equivalence point The point at which stoichiometrically equivalent amounts of the acid and base have reacted. 7. End point The point at which the indicator changes color and the titration is stopped. 55

56 Titrations 56

57 Titration Curves Strong Acid/Strong Base Titration Curves These graphs are a plot of ph vs. volume of acid or base added in a titration. As an example, consider the titration of ml of M perchloric acid with M potassium hydroxide. In this case, we plot ph of the mixture vs. ml of KOH added. Note that the reaction is a 1:1 mole ratio. HClO KOH KClO H O

58 Strong Acid/Strong Base Titration Curves Before any KOH is added the ph of the HClO 4 solution is Remember perchloric acid is a strong acid that ionizes essentially 100%. HClO H ClO M ph [ ] H 100% 0.100M 0.100M log(0.100) M 58

59 Strong Acid/Strong Base Titration Curves After a total of 0.0 ml M KOH has been added the ph of the reaction mixture is? Start Change After rxn. M : HClO 4 : - HClO mmol mmol mmol mmol HClO 10 ml [ ] H M ph KOH.0 mmol mmol mmol 4 KClO M 4 H mmol mmol O 59

60 Strong Acid/Strong Base Titration Curves After a total of 50.0 ml of M KOH has been added the ph of the reaction mixture is? Start Change After rxn. M : HClO 4 : HClO mmol mmol mmol mmol HClO 150 ml [ ] H 0.0M ph KOH mmol mmol mmol 4 KClO M 4 H mmol mmol O 60

61 Strong Acid/Strong Base Titration Curves After a total of 90.0 ml of M KOH has been added the ph of the reaction mixture is? Start Change After rxn. M : HClO 4 : HClO mmol mmol mmol mmol HClO 190 ml mmol [ ] H 0.005M ph.8 4 KOH mmol mmol 4 KClO M 4 H mmol mmol O 61

62 Strong Acid/Strong Base Titration Curves After a total of ml of M KOH has been added the ph of the reaction mixture is? Start : HClO4 KOH KClO4 HO 10.0 mmol 10.0 mmol Change :-10.0 mmol mmol After 0.0 mmol 0.0 mmol rxn. No acid or base neutral ph mmol 10.0 mmol 6

63 Strong Acid/Strong Base Titration Curves We have calculated only a few points on the titration curve. Similar calculations for remainder of titration show clearly the shape of the titration curve. 6

64 Using Solutions in Chemical Reactions Combine the concepts of molarity and stoichiometry to determine the amounts of reactants and products involved in reactions in solution. 64

65 Using Solutions in Chemical Reactions Example 10-9: What volume of M BaCl is required to completely react with 4. g of Na SO 4? Na SO BaCl BaSO 4 4 NaCl 65

66 Using Solutions in Chemical Reactions Example 10-9: What volume of M BaCl is required to completely react with 4. g of Na SO 4? Na SO? L BaCl 4 BaCl 4. gna SO BaSO 4 4 NaCl 1mol Na 14 g Na SO SO

67 Using Solutions in Chemical Reactions Example 10-9: What volume of M BaCl is required to completely react with 4. g of Na SO 4? Na SO? L BaCl 1mol BaCl 1mol Na SO 4 BaCl 4. gna 4 SO BaSO 1mol 14 g 1L BaCl mol BaCl 4 4 NaCl Na Na SO SO L 67

68 Using Solutions in Chemical Reactions Example 10-10: (a)what volume of 0.00 M NaOH will react with 50.0 ml 0f 0.00 M aluminum nitrate, Al(NO )? ( NO ) NaOH Al( OH) Al NaNO 68

69 Using Solutions in Chemical Reactions Example 10-10: (a)what volume of 0.00 M NaOH will react with 50.0 ml 0f 0.00 M aluminum nitrate?? Al ml ( NO ) NaOH 0.00 mol Al(NO 1 L Al(NO ) 1 L NaOH 0.00 mol NaOH 50.0 NaOH L Al(OH) or 150 ml NaNO 1 L ml Al(NO ) sol' n 1000 ml ) sol' n mol NaOH sol' n 1 mol Al(NO ) NaOH sol' n 69