Amount of substance dissolved in 1 L of water

Transcription

1 Chapter 7: Phenomena Phenomena: Scientists dissolved different substances in water and then measured the [H + ] and [OH - ] concentrations in each solution. What patterns do you notice about the substances? Substance Amount of substance dissolved in 1 L of water [H + ] [OH - ] HCl 1.0 mol 1.0 M M KOH 1.0 mol M 1.0 M HC 2 H 2 ClO mol M M HBr 1.0 mol 1.0 M M HOCl 1.0 mol M M CH 3 NH mol M M NH mol M M HNO mol 1.0 M M NaOH 1.0 mol M 1.0 M C 5 H 5 N 1.0 mol M M H 2 O N/A

2 Big Idea: A Bronsted-Lowry acid is a proton donor and a Bronsted-Lowry base is a proton acceptor. After an acid/base loses/gains its proton it becomes a conjugate base/acid. Acids and bases can either completely dissociate (strong) or incompletely dissociate (weak). An equilibrium problem must be set up to solve for the ph of a weak acid or base. Chapter 7 Acids and Bases Acids and Bases Conjugate Acids/Bases Strength of Acids/Bases ph/poh Scales ph/poh of Strong Acids/Bases ph/poh of Weak Acids/Bases Acid/Base Properties of Salts Acid Rain 2

3 Acids and Bases Acid Sour taste (lemon citric acid) Dissolve many metals (Acid(aq) + metal(s) salt(aq) + H 2 (g)) Turn litmus paper red Base Bitter taste (unsweetened baker s chocolate) Slippery feel (cleaning products) Turn litmus paper blue 3

4 Acids and Bases Arrhenius (1884) Acid: A compound that forms hydrogen ions (H + ) in water. Examples: HCl(aq) acid CH 4 (aq) not an acid because it does not release (H + ) ions in solution Base: A compound that forms hydroxide ions (OH - ) in water. Examples: NaOH(aq) base NH 3 base because NH 3 (aq) + H 2 O(l) NH 4+ (aq) + OH - (aq) Bronsted-Lowry (1923) Acid: A proton donor. Base: A proton acceptor. 4

5 Acids and Bases Deprotonation: The loss of a proton from a Bronsted-Lowry acid Note: First deprontination is the loss of the first H, the second deprotination is the loss of a second H, and the third deprotination is the loss of a third H. Amphoteric: A substance that can act as an acid or base Example: H 2 O 5

6 Acids and Bases Conjugate Acid Base Pair: Two substances that are related to each other by the transfer of one proton Acid donates a proton Conjugate Base Base accepts a proton Conjugate Acid 6

7 Conjugate Acids/Bases Student Question Which of the following represent conjugate acid-base pairs? For those pairs that are not conjugates, write the correct conjugate acid or base for each species in the pair. a) H 2 SO 4 and SO 2-4 b) H 2 PO 4- and HPO 2-4 c) HClO 4 and Cl - d) NH 4+ and NH - 2 7

8 Strength of Acids/Bases Strong Acid or Base: An acid/base that completely ionizes in solution. Weak Acid or Base: An acid/base that does not completely ionize in solution. Strong Acids HCl HNO 3 HBr HClO 4 HI HClO 3 HBrO 3 HBrO 4 H 2 SO 4 HIO 4 Strong Bases LiOH Sr(OH) 2 NaOH Ca(OH) 2 KOH Ba(OH) 2 RbOH Mg(OH) 2 CsOH 8

9 Strength of Acids/Bases Name Formula K a Hydrogen Sulfate Ion HSO Chlorous Acid HClO Monochloracetic Acid HC 2 H 2 ClO Hydrofluoric Acid HF Nitrous Acid HNO Acetic Acid HC 2 H 3 O Hydrated Aluminum(III) Ion [Al(H 2 O) 6 ] Hypochlorous Acid HOCl Hydrocyanic Acid HCN Ammonium Ion NH Phenol HOC 6 H Note: A strong acid is defined as an acid that has a K a larger than 1. Not all strong acids have the same K a. For example the K a of H 3 O + is 55, whereas the K a of HCl is Therefore, H 3 O + is one of the weakest strong acids. 9

10 Strength of Acids/Bases Name Formula K b Ammonia NH Methylamine CH 3 NH Ethylamine C 2 H 5 NH Aniline C 6 H 5 NH Pyridine C 5 H 5 N Note: The stronger the base, the larger the K b. 10

11 Strength of Acids/Bases Student Question The K a values for HPO 4 2- and HSO 3- are and respectively. Therefore, it follows that HPO 4 2- is a acid than HSO 3- and PO 4 3- is a base than SO a) weaker, weaker b) weaker, stronger c) stronger, weaker d) stronger, stronger 11

12 Strength of Acids/Bases Is there a relationship between K a and K b? General Weak Acid Equilibrium Equation HA(aq) H + (aq) + A - (aq) K a = H+ A HA General Weak Base Equilibrium Equation B(aq) + H 2 O(l) BH + (aq) + OH - (aq) K b = BH+ OH Water Equilibrium Equation B H 2 O(l) H + (aq) + OH - (aq) K W = H + OH = Note: K W is known as the ion product constant. 12

13 ph/poh Scale How do you tell if a solution acidic, basic, or neutral? [H + ] = [OH - ] [H + ] > [OH - ] [H + ] < [OH - ] neutral acidic basic Are the [H + ] and [OH - ] related? K W = H + OH = For neutral solutions H + = OH = [H + ] > and [OH - ] < [H + ] < and [OH - ] > How do you calculate ph? ph=-log[h + ] ph = 7 ph < 7 ph > 7 neutral acidic basic acidic basic 13

14 ph/poh Scale Lye Milk of magnesia Average seawater Alkaline soil Neutral (above 7) Theoretical ph of rain Acidic soil ( ) Most acidic rainfall recorded in U.S. Vinegar Ammonia Baking soda Milk Human blood Tomato juice Battery acid Apples Lemon juice 14

15 ph/poh of Strong Acids/Bases Student Question Calculate the ph of 0.25 M Ba(OH) 2. a) 0.60 b) c) d) e) None of the above 15

16 ph/poh of Weak Acids/Bases Student Question What is the ph of a 0.18 M monoprotic acid solution whose conjugate base has a K b = 2.8 x10-8? a) 3.22 b) 2.85 c) 3.90 d) 4.70 e) None of the above 16

17 Acid/Base Properties of Salts Student Question Is NH 4 C 2 H 3 O 2 : Helpful Information: K b NH 3 = and K a HC 2 H 3 O 2 = a) Acid b) Base c) Neutral d) More information needed 17

18 Acid Rain ph water ~7, ph of unpolluted rain ~5.7 ph of rain in industrial areas has been recorded at ~2.4 18

19 Acid Rain What are the natural causes of acids in rain? Source CO 2 NO SO 2 Causes Decomposition/Respiration/Fires What are the man made causes of acids in rain? Source CO 2 NO SO 2 Electrical Discharge Volcanic Gases Causes Fossil Fuel Combustion/Fires High Temperature Air Combustion Fossil Fuel Combustion 19

20 Acid Rain CO 2 (produced from the combustion of C or C x H y ) Coal C(s) + O 2 (g) CO 2 (g) Gas CH 4 (g) + 2O 2 (g) CO 2 (g) + 2H 2 O(g) CO 2 (g) + H 2 O(l) H 2 CO 3 (aq) NO (formed from N at high temperatures) N 2 (g) + O 2 (g) heat 2NO(g) 2NO(g) + O 2 (g) 2NO 2 (g) 3NO 2 (g) + H 2 O(l) 2HNO 3 (aq) + NO(g) Note: The majority of the NO emissions come from automobiles. 20

21 Acid Rain SO 2 (formed from the combustion of S) S(s) + O 2 (g) SO 2 (g) 2SO 2 (g) + O 2 (g) 2SO 3 (g) SO 3 (g) + H 2 O(l) H 2 SO 4 (aq) Note: The majority of all SO 2 emissions come from the production of electricity. Note: Why are we more worried about controlling SO 2 and NO emissions for acid rain? 21

22 Acid Rain NO Three Way Catalytic converters (1981) 2NO(g) Pt or Rh N 2 (g) + O 2 (g) SO 2 Scrubbers (in the 1990) (limestone slurries are put into the smoke stacks) CaCO 3 (s) + H 2 SO 4 (aq) CaSO 4 (aq) + H 2 O(l) +CO 2 (g) Note: Acid rain level have dropped 65% since

23 Take Away From Chapter 7 Big Idea: A Bronsted-Lowery acid is a proton donor and a Bronsted-Lowery base is a proton acceptor. After an acid/base loses/gains its proton it becomes a conjugate base/acid. Acids and bases can either completely dissociate (strong) or incompletely dissociate (weak). An equilibrium problem must be set up to solve for the ph of a weak acid or base. Acids and Bases Know the different acid/base definitions. Arrhenius Acid: Forms H + in water Base: Forms OH - in water Bronsted-Lowery Acid: Proton donor Base: Proton acceptor 23 Numbers correspond to end of chapter questions.

24 Take Away From Chapter 7 Conjugate Acids/Bases (20) Be able to recognize conjugate acid base pairs. Pairs that differ by 1 hydrogen atom (H 3 PO 4 and H 2 PO 4- ). Strength of Acids/Bases Memorize the strong acids and bases. (24,33) Strong Acids: HCl, HBr, HI, HNO 3, HBrO 3, HBrO 4, HIO 3, HIO 4 HClO 4, HClO 3, and H 2 SO 4 (1 st deprotonation) Strong Bases: LiOH, NaOH, KOH, RbOH, CsOH, Sr(OH) 2, Ca(OH) 2, Ba(OH) 2, and Mg(OH) 2 Know the relationship between [H + ] and [OH - ] (40,41) [H + ][OH - ]= Be able to change between K a and K b values. K a = K w K b 24 K b = K w K a Know that the stronger the acid/base the weaker the conjugate acid/base. (31) Be able to order acids/bases in increasing strength using K a and/or K b values (27,28,29,30,69,70) Numbers correspond to end of chapter questions.

25 Take Away From Chapter 7 ph/poh Scale (74,75) Be able to calculate the ph of a solution. ph = log H + Be able to calculate the poh of a solution. poh = log OH Be able to convert between ph and poh 14 = ph + poh ph/poh of Strong Acids/Bases Be able to calculate the ph and poh of strong acids and strong bases. ph/poh of Weak Acids/Bases (79) Be able to identify the major species in solution. (51) Be able to calculate the ph and poh of weak acids and bases (ICE table). (47,48,49,52,53,55,61,65) Be able to calculate the water solubility of a substance given the ph of a saturated solution. (56) 25 Numbers correspond to end of chapter questions.

26 Take Away From Chapter 7 Acid/Base Properties of Salts (101,103,105,109,131) Be able to determine if a salt is an acidic, basic, or neutral Be able to calculate the ph of a salt with only one acid anion or cation Acid Rain 26 Numbers correspond to end of chapter questions.