Ch10. Acids. A unique class of substance and its complement. Acids & Bases. version 1.5

Transcription

1 Ch10 Acids A unique class of substance and its complement. Acids & Bases. version 1.5 Nick DeMello, PhD

2 Ch10 Acids Acids & Bases Sources & Properties Liebig Model Arrhenius Model Provides H + & OH 1- Naming Brønsted-Lowry Model Accepts/Donates H + Solvent Effects Conjugate Base Pairs Identifying Pairs 1 H + 1 Acid Strength Dissociation/Association Acids are Electrolytes Strong & Weak Acids Base Strength Equilibrium Reversible Reactions Reaction Rates Achieving Equilibrium Le Chatelier s Principle Disturbing Equilibrium Re-establishing Equilibrium

3 Acids & Bases For more than 300 years, substances that behaved like vinegar have been classified as acids. Substances that have properties like the ash from a wood fire have been called alkalies or bases. The name "acid" comes from the Latin acidus, which means "sour," and refers to the sharp odor and sour taste of many acids. Vinegar tastes sour because it is a dilute solution of acetic acid in water. Lemon juice is sour because it contains citric acid. Milk turns sour when it spoils because of the formation of lactic acid. The sour odor of rotten meat is due to carboxylic acids such as butyric acid formed when fat spoils.

4 Acids & Bases For more than 300 years, substances that behaved like vinegar have been classified as acids. Substances that have properties like the ash from a wood fire have been called alkalies or bases. The name "acid" comes from the Latin acidus, which means "sour," and refers to the sharp odor and sour taste of many acids. Vinegar tastes sour because it is a dilute solution of acetic acid in water. Lemon juice is sour because it contains citric acid. Milk turns sour when it spoils because of the formation of lactic acid. The sour odor of rotten meat is due to carboxylic acids such as butyric acid formed when fat spoils.

5 Sources and Uses Acids are all around us. and are used for diverse purposes. 5

6 Properties Acids: 1. Taste sour. 2. Turn litmus red. 3. Destroy the properties of bases. 4. Conduct electricity. 5. Produce H2 gas from active metals. Bases have the properties of: 1. Taste bitter (or chalky). 2. Turn litmus blue. 3. Destroy the properties of acids. 4. Conduct electricity. 5. Feel slippery ( soapy ). Litmus is a water soluble mixture of different dyes extracted from lichens. It is often absorbed onto filter paper to produce one of the oldest forms of ph indicator, used to test materials for acidity. Litmus was used for the first time about 1300 AD by Spanish alchemist Arnaldus de Villa Nova. 6

7 Svante Arrhenius Justus Liebig proposed that an acid was a hydrogen-containing substance in which the hydrogen could be replaced by a metal. This definition lasted for over 50 years until a better one came along. Svante Arrhenius 1883 doctoral thesis presented the idea of electrolytic dissociation that electrolytes dissociate into ions when placed in water. (At the time, it was thought you needed electric current to form ions.) Arrhenius got a D for his thesis. It became one of the most widely utilized ideas of the next 1,000 years. Arrhenius is seen as one of the greatest chemists of that millennia. He was awarded the nobel price in 1903 for that idea the one he got a D on. From the theory of electrolytic dissociate, Arrhenius defined: Acid is any substance which delivers hydrogen ion (H + ) to the solution. 7 acid HCl(g) H 2 O(l) H + (aq) + Cl (aq) Base is any substance which delivers hydroxide ion (OH ) to the solution. H 2 O(l) KOH base OH - (aq) + K + (aq)

8 Naming Binary Acids Binary compounds where one of the two non-metals is hydrogen are not acids. But some become acids when they re dissolved in water. Binary compounds only release protons into water. The binary compounds that become acids are: HF, HCl, HBr, and HI We indicate something is dissolved in water by putting (aq) after it s formula. Aqueous is Latin for with water. To name a binary acid add -ic acid to the anion and prefix the name with hydro. HBr is hydrogen bromide. It s not an acid. HBr (aq) is hydrobromic acid. HCl (aq) is hydrochloric acid, a very powerful acid. 1 H H + + What s the name or formula? Hydrogen Bromide Hydrobromic Acid Hydroiodic Acid HF HCl (aq) Answer: HBr HBr (aq) HI (aq) Hydrogen Fluoride Hydrochloric Acid 8

9 Naming Oxy-Acids Polyatomic ions with enough hydrogens on them to neutralize their charge become acids. Oxy acids do not need to be in water to be acids, they are acids with or without (aq). To name acids of oxy-ions, replace the -ate ion with -ic acid the -ite ion with -ous acid P PO4 3- Phosphate ion H3PO4 Phosphoric acid PO3 3- Phosphite ion H3PO3 Phosphorous acid S SO4 2- Sulfate ion H2SO4 Sulfuric acid SO3 2- Sulfite ion H2SO3 Sulfurous acid C CO3 2- Carbonate Ion H2CO3 Carbonic acid CO2 2- Carbonite Ion H2CO2 Carbonous acid N NO3 1- Nitrate Ion HNO3 Nitric acid NO2 1- Nitrite Ion HNO2 Nitrous acid Cl,Br, I ClO4 1- Perchlorate Ion HClO4 Perchloric acid ClO3 1- Chlorate Ion HClO3 Chloric acid ClO2 1- Chlorite Ion HClO2 Chlorous acid ClO 1- Hypochlorite Ion HClO Hypochlorous acid 9

10 Arrhenius Bases Arrhenius bases produce hydroxide ions (OH ) in water taste bitter or chalky are also electrolytes because they produce hydroxide ions (OH 1 ) in water feel soapy and slippery turn litmus indicator paper blue and phenolphthalein indicator pink Typical Arrhenius bases are named as hydroxides. NaOH sodium hydroxide KOH potassium hydroxide Ba(OH)2 barium hydroxide Al(OH)3 aluminum hydroxide 10

11 Naming Acids & Bases What is the name of each of the following? Match the formulas with the names. HBr (aq) H2CO3 A. bromic acid B. bromous acid C. hydrobromic acid A. carbonic acid B. hydrocarbonic acid C. carbonous acid D E B 1. HNO 2 A. iodic acid 2. Ca(OH) 2 B. sulfuric acid 3. H 2 SO 4 C. sodium hydroxide A C 4. HIO 3 D. nitrous acid 5. NaOH E. calcium hydroxide HBrO2 A. bromic acid B. hydrobromous acid C. bromous acid 11

12 Ch10 Acids Acids & Bases Sources & Properties Liebig Model Arrhenius Model Provides H + & OH 1- Naming Brønsted-Lowry Model Accepts/Donates H + Solvent Effects Conjugate Base Pairs Identifying Pairs 1 H + 1 Acid Strength Dissociation/Association Acids are Electrolytes Strong & Weak Acids Base Strength Equilibrium Reversible Reactions Reaction Rates Achieving Equilibrium Le Chatelier s Principle Disturbing Equilibrium Re-establishing Equilibrium

13 Problems with Arrhenius Model The Arrhenius model of acids has some problems It says solvents play no role in acidity. HCl is an acid only in water, in benzene it s not. It says salts should not produce only neutral solutions. NaCl in water is acidic. It caused Arrhenius to suggest the base of ammonia in water is NH4OH. The actual base is NH3. NH3 is just as basic in aniline, where no hydroxide is possible. H + (a bare proton) doesn t last long in water. The lone pairs on water grab it. Even in the strongest aqueous acid solutions the concentration of H + is something like M The Arrhenius theory of acids and bases was replaced by the theory proposed independently by Johannes Brønsted and Thomas Lowry in

14 Brønsted-Lowry Model The Brønsted Lowry theory is an acid base reaction theory which was proposed independently by Johannes Nicolaus Brønsted and Thomas Martin Lowry in When an acid and a base react with each other, the acid forms its conjugate base, and the base forms its conjugate acid by exchange of a proton. According to the Brønsted Lowry theory: an acid is a substance that donates H 1+ a base is a substance that accepts H 1+ Johannes Brønsted Thomas Lowry 14

15 Brønsted-Lowry Model According to the Brønsted Lowry theory: an acid is a substance that donates H 1+ a base is a substance that accepts H 1+ In the reaction of ammonia and water, NH3 acts as the base that accepts H+ H2O acts as the acid that donates H+ One either side of the arrow, there is one acid and one base. The one that s holding the traded H + is the acid. 15

16 Identify the Acid In each of the following equations, identify the Brønsted Lowry acid and base in the reactants: A B HNO3 (aq) + H2O(l) H3O + (aq) + NO 3 (aq) ACID BASE NH3 (aq) + H3O + (l) H2O (aq) + NH4 1+ (aq) BASE ACID 16

17 17 Summary of Acid-Base Properties

18 Ch10 Acids Acids & Bases Sources & Properties Liebig Model Arrhenius Model Provides H + & OH 1- Naming Brønsted-Lowry Model Accepts/Donates H + Solvent Effects Conjugate Base Pairs Identifying Pairs 1 H + 1 Acid Strength Dissociation/Association Acids are Electrolytes Strong & Weak Acids Base Strength Equilibrium Reversible Reactions Reaction Rates Achieving Equilibrium Le Chatelier s Principle Disturbing Equilibrium Re-establishing Equilibrium

19 Conjugate Acid Base Pairs In any acid base reaction, there are two conjugate acid base pairs, and each pair is related by the loss and gain of H +1 each pair is tossing a ball back and forth, the ball is H 1+ one pair occurs in the forward direction one pair occurs in the reverse direction acid and conjugate base pair 1 HA + B A 1- + BH 1+ acid and conjugate base pair 2 19

20 Conjugate Acid Base Pairs Conjugate base pair is the same substance, with and without the proton (hydrogen ion) it is either donating or accepting. HA and A 1- are one acid base conjugate pair. HA is the acid. A 1- is the base. HA + B A 1- + BH B and BH 1+ are the other acid base conjugate pair. B is the base. BH 1+ is the acid.

21 Conjugate Acid Base Pairs In the acid base reaction of HF and water the first conjugate acid base pair is HF, which donates H + to form its conjugate base, F the other conjugate acid base pair is H 2 O, which accepts H + to form its conjugate acid, H 3 O + each pair is related by a loss and gain of H + 21

22 Conjugate Acid Base Pairs In acid-base reaction of ammonia (NH 3 ) and water one conjugate acid base pair is NH 3 /NH 4 + the other conjugate acid base pair is H 2 O/H 3 O + 22

23 Write the conjugate base for ACID BASE HBr H 1+ + Br 1- HNO 3 H 1+ + NO 1-3 H 3 PO 4 H 1+ + H 2 PO 1-4 NH 1+ 4 H 1+ + NH 3 H 2 CO 3 H 1+ + HCO 1-3 H3O 1+ H 1+ + H 2 O (water)

24 Write the conjugate acid for BASE ACID Cl 1- + H 1+ HCl BrO H 1+ HBrO 3 HPO H 1+ H 2 PO 1-4 OH 1- + H 1+ H 2 O (water) NH 3 + H 1+ NH 1+ 4 H 2 O + H 1+ H 3 O 1+ (hydronium ion)

25 Ch10 Acids Acids & Bases Sources & Properties Liebig Model Arrhenius Model Provides H + & OH 1- Naming Brønsted-Lowry Model Accepts/Donates H + Solvent Effects Conjugate Base Pairs Identifying Pairs 1 H + 1 Acid Strength Dissociation/Association Acids are Electrolytes Strong & Weak Acids Base Strength Equilibrium Reversible Reactions Reaction Rates Achieving Equilibrium Le Chatelier s Principle Disturbing Equilibrium Re-establishing Equilibrium

26 Acid Strength H 2 O NaCl(aq) Na + (aq) + Dissocia'on of sodium chloride in water Cl - (aq) 26 Acids are electrolytes. Electrolyte strength describes the dissociation process of electrolytes. The stronger they are, the more they break apart. The stronger they are, the more ions they put into solution. Acid and base strength is the same process. Strong acids, put more H + into solution. Stronger bases, put more OH 1- (or other proton accepters) into solution.

27 Acid Strength H 2 O HI(s) H + (aq) + I - (aq) Strong acids dissociate completely into ions. They produce high concentra'ons of H + 27 Acids are electrolytes. Electrolyte strength describes the dissociation process of electrolytes. The stronger they are, the more they break apart. The stronger they are, the more ions they put into solution. Acid and base strength is the same process. Strong acids, put more H + into solution. Stronger bases, put more OH 1- (or other proton accepters) into solution.

28 Acid Strength H 2 O HF(aq) H + (aq) + Weak acids dissolve in water, but remain mostly an associated pair of ions. F - (aq) They produce low concentra'ons of H + 28 Acids are electrolytes. Electrolyte strength describes the dissociation process of electrolytes. The stronger they are, the more they break apart. The stronger they are, the more ions they put into solution. Acid and base strength is the same process. Strong acids, put more H + into solution. Stronger bases, put more OH 1- (or other proton accepters) into solution.

29 Acid Strength H 2 O HB(aq) H + (aq) + B - (aq) There are six common strong acids. 29 Acids are electrolytes. Electrolyte strength describes the dissociation process of electrolytes. The stronger they are, the more they break apart. The stronger they are, the more ions they put into solution. Acid and base strength is the same process. Strong acids, put more H + into solution. Stronger bases, put more OH 1- (or other proton accepters) into solution.

30 Acid Strength The stronger an acid is at donating H, the weaker the conjugate base is at accepting H. Higher oxidation number = stronger oxyacid More oxygens in oxyacid = stronger acid H 2 SO 4 > H 2 SO 3 HNO 3 > HNO 2 Cations are stronger acids than neutral molecules. Neutral molecules are stronger acids than anions. H 3 O + > H 2 O > OH ; NH 4 + > NH3 > NH 2 Trend in base strength opposite 30

31 Ch10 Acids Acids & Bases Sources & Properties Liebig Model Arrhenius Model Provides H + & OH 1- Naming Brønsted-Lowry Model Accepts/Donates H + Solvent Effects Conjugate Base Pairs Identifying Pairs 1 H + 1 Acid Strength Dissociation/Association Acids are Electrolytes Strong & Weak Acids Base Strength Equilibrium Reversible Reactions Reaction Rates Achieving Equilibrium Le Chatelier s Principle Disturbing Equilibrium Re-establishing Equilibrium

32 Acid Base Equilibrium Acid Base reactions are reversible. Forward Reaction HF(aq) + H 2 O(l) F (aq) + H 3 O + (aq) Reverse Reaction In reversible reactions, two reactions are taking place. The reaction is occurring in both the forward and reverse direction. Forward Reaction HF(aq) + H 2 O(l) F (aq) + H 3 O + (aq) Reverse Reaction F (aq) + H 3 O + (aq) HF(aq) + H 2 O(l) 32

33 Acid Base Equilibrium Acid Base reactions are reversible. Forward Reaction HF(aq) + H 2 O(l) F (aq) + H 3 O + (aq) Reverse Reaction Reactants Products Even though there are two reactions going on, by convention we always refer to: The substances on the left as reactants. The substances on the right as products. The rate of the forward reaction depends on how much reactant. The rate of the reverse reaction depends on how much product. 33

34 Acid Base Equilibrium Acid Base reactions are reversible. Forward Reaction HF(aq) + H 2 O(l) F (aq) + H 3 O + (aq) Reverse Reaction As an analogy thinking of population across a border. When Country A citizens feel overcrowded, some will emigrate to Country B. When you first dissolve HF in solution, the forward reaction goes faster than the reverse. 34

35 Acid Base Equilibrium Acid Base reactions are reversible. Forward Reaction HF(aq) + H 2 O(l) F (aq) + H 3 O + (aq) Reverse Reaction The rate of reaction changes with concentration. As we have less reactant the forward reaction slows. As we have more product, the reverse reaction speeds up. Eventually the two rates are equal. The concentration of reactants and products becomes constant. Even though both reactions are continuing to occur. 35

36 Acid Base Equilibrium Acid Base reactions are reversible. Forward Reaction HF(aq) + H 2 O(l) F (aq) + H 3 O + (aq) Reverse Reaction As an analogy thinking of population change in countries. However, after a time, emigration will occur in both directions at the same rate, leading to populations in Country A and Country B that are constant, but not necessarily equal. That dynamic is Equilibrium 36

37 Fill in the Blanks Complete each of the following with equal or not equal faster or slower change or do not change: A. Before equilibrium is reached, the concentrations of the reactants and products. change (change or do not change?) B. Initially, reactants have a rate of reaction faster than the rate of reaction of the products. (faster or slower?) C. At equilibrium, the rate of the forward reaction is equal to the rate of the reverse reaction. (equal or not equal?) D. At equilibrium, the concentrations of the reactants and products. do not change (change or do not change?) 37

38 Ch10 Acids Acids & Bases Sources & Properties Liebig Model Arrhenius Model Provides H + & OH 1- Naming Brønsted-Lowry Model Accepts/Donates H + Solvent Effects Conjugate Base Pairs Identifying Pairs 1 H + 1 Acid Strength Dissociation/Association Acids are Electrolytes Strong & Weak Acids Base Strength Equilibrium Reversible Reactions Reaction Rates Achieving Equilibrium Le Chatelier s Principle Disturbing Equilibrium Re-establishing Equilibrium

39 Le Châtelier s Principle When we alter the concentration of a reactant or product of a system at equilibrium, the rates of the forward and reverse reactions will no longer be equal a stress is placed on the equilibrium Le Châtelier s principle states that when equilibrium is disturbed, the rates of the forward and reverse reactions change to relieve that stress and reestablish equilibrium. 39

40 Le Châtelier s Principle Le Châtelier s principle predicts how disturbances will effect reaction rates. Forward Reaction HF(aq) + H 2 O(l) F (aq) + H 3 O + (aq) Reverse Reaction When the populations of Country A and Country B are in equilibrium, the emigration rates between the two countries are equal so the populations stay constant. That dynamic is Equilibrium 40

41 Le Châtelier s Principle Le Châtelier s principle predicts how disturbances will effect reaction rates. Forward Reaction HF(aq) + H 2 O(l) F (aq) + H 3 O + (aq) Reverse Reaction When an influx of population enters Country B from somewhere outside Country A, it disturbs the equilibrium established between Country A and Country B. 41

42 Le Châtelier s Principle Le Châtelier s principle predicts how disturbances will effect reaction rates. Forward Reaction HF(aq) + H 2 O(l) F (aq) + H 3 O + (aq) Reverse Reaction The result will be people moving from Country B into Country A faster than people moving from Country A into Country B. This will continue until a new equilibrium between the populations is established; the new populations will have different numbers of people than the old ones. 42

43 Le Châtelier s Principle Le Châtelier s principle predicts how disturbances will effect reaction rates. Forward Reaction HF(aq) + H 2 O(l) F (aq) + H 3 O + (aq) Reverse Reaction 43

44 Le Châtelier s Principle Le Châtelier s principle predicts how disturbances will effect reaction rates. Forward Reaction HF(aq) + H 2 O(l) F (aq) + H 3 O + (aq) Reverse Reaction Shift Equilibrium to Adding F - will Removing HF will Removing H 3 O + will Reactants Reactants Products 44

45 Ch10 Acids Acids & Bases Sources & Properties Liebig Model Arrhenius Model Provides H + & OH 1- Naming Brønsted-Lowry Model Accepts/Donates H + Solvent Effects Conjugate Base Pairs Identifying Pairs 1 H + 1 Acid Strength Dissociation/Association Acids are Electrolytes Strong & Weak Acids Base Strength Equilibrium Reversible Reactions Reaction Rates Achieving Equilibrium Le Chatelier s Principle Disturbing Equilibrium Re-establishing Equilibrium

46 46 Questions?