Acids Bases and Salts and Covalent Solutes Chapter

Acids, Bases and Salts and Covalent Solutes Chapter 14 Tro, 2 nd ed. 1

Acids and Bases: Acid Properties “Sour taste” Change the color of litmus from blue to red These properties are due to the release +, into water. of hydrogen ions, H React with: - metals such as zinc and magnesium to produce hydrogen gas - strong bases to produce water and an ionic compound (salt) - carbonates to produce carbon dioxide. 2

Acids and Bases: Base Properties Bitter or caustic taste Have a slippery, soapy feeling. Change the color of litmus from red to blue React with acids These properties are due to the release of hydroxide ions, OH+, into water. 3

Acid-base Theories An Arrhenius acid “is a hydrogencontaining substance that dissociates to produce hydrogen ions. ” Strong: HA(aq) + H 2 O(l) → H 3 O+(aq) + A-(aq) Weak: HA(aq) + H 2 O(l) H 3 O+(aq) + A-(aq) (List your six acids again and sort them as being weak or strong. ) 4

Acid-base Theories An Arrhenius base is a substance that dissociates or reacts with water to produce hydroxide ions in aqueous solution. Strong: MOH(aq) → M+(aq) + OH-(aq) Weak: BH(aq) + H 2 O(l) BH 2+(aq) + OH-(aq) Strong bases are groups I and II metal hydroxides; weak bases are ammonia and amines. 5

Arrhenius Theory: Figure 14. 9 HCl ionizes in water, producing H+ and Cl– ions Na. OH dissociates in water, producing Na+ and OH– ions 6

Acid-base Theories A Bronsted-Lowry acid is a proton (H+) donor. proton acceptor Bronsted-Lowry Acid Bronsted-Lowry Base proton donor HCl(aq) + H 2 O(l) → H 3 O+(aq) + Cl-(aq) A Bronsted-Lowry base is a proton (H+) acceptor. 7

ionion ishydrogen ion ahydrogen hydronium does formed not existcombines with water in water 8

Conjugate acid-base pairs differ by a proton. When an acid donates a proton it becomes the conjugate base. HCl acid → Cl. Conj. base When a base accepts a proton it becomes the conjugate acid. H 2 O base → H 3 O + Conj. acid 9

Conjugate acid-base pairs are identified in an acid-base reaction. HCl(g) + H 2 O (l) → Cl-(aq) + H 3 O+(aq) acid base conj acid 10

Bronsted-Lowry: acid-conj base and base-conj acid Practice: You identify the conjugate acid-base pairs in each of the following reactions. 1. H 2 CO 3(aq) + CN-(aq) HCN(aq) + HCO 3 -(aq) 2. H 2 O(l) + HCl(aq) H 3 O+(aq) + Cl-(aq) 3. H 2 O(l) + CH 3 COOH(aq) H 3 O+(aq) + CH 3 COO-(aq) 11

Acid-base Theories: A Lewis acid is an electron-pair acceptor. A Lewis base is an electron-pair donor. Electron Pair Lewis Acid Acceptor Electron pair donated to H+ Lewis Base Electron Pair Donor 12

Electron Pair Lewis Acid Acceptor Electron pair donated to B Lewis Base Electron Pair Donor 13

14

DEFINITIONS: Monoprotic acid: can donate only one proton: HF, HCl, HNO 3 Polyprotic acid: can donate > 2 protons: H 2 SO 4, H 3 PO 4 (Apply to bases as well in accepting protons: CO 32 - can accept two protons. ) 15

Reactions of Acids In aqueous solution, the H+ or H 3 O+ ions are responsible for the characteristic reactions of acids Reaction with Metals: Acids react with metals that lie above hydrogen in the activity series of element to produce hydrogen and an ionic compound (salt) acid + metal → hydrogen + ionic compound Reaction with Metals Oxidizing acids react with metals to produce water instead of hydrogen acid + metal → water + ionic compound 16

Reactions of Acids Reaction with Bases The reaction of an acid with a base is called a neutralization reaction. In an aqueous solution the products are a salt and water: HBr(aq) + KOH(aq) → KBr(aq) + H 2 O(l) 2 HNO 3(aq) + Ca(OH)2(aq) → Ca(NO 3)2(aq) + 2 H 2 O(l) 17

Reactions of Acids Reaction with Metal Oxides In an aqueous solution the products are a salt and water. This type of reaction is closely related to that of an acid with a base: 2 HCl(aq) + Na 2 O(s) → 2 Na. Cl(aq) + H 2 O(l) H 2 SO 4(aq) + Mg. O(s) → Mg. SO 4(aq) + H 2 O(l) 18

Reactions of Acids Reaction with Carbonates Most acids react with carbonates to produce carbon dioxide, water and an ionic compound: H 2 SO 4(aq) + Mg. CO 3(s) →Mg. SO 4(aq) +H 2 O(l) +CO 2(g) HCl(aq) + Na. HCO 3(aq) → Na. Cl(aq) + H 2 O(l) + CO 2(g) 19

SALTS Salts can be considered compounds derived from acids and bases. They consist of positive metal or ammonium ions combined with nonmetal ions (OH- and O 2 - excluded). Salts are crystalline solids and have very high MPs and BPs. We use the terms salt and ionic compound interchangeably. 20

Electrolytes are solutes whose aqueous solutions can carry an electrical current because they are charged particles (ions). Salts: water-soluble ionic compounds are all strong electrolytes. Acids: form H+ ions in water along with their anions; strong acids are strong electrolytes; weak acids are weak electrolytes. Bases: form OH- in water along with their cations; strong bases are strong electrolytes; weak bases are weak electrolytes. Covalent solutes: do not form ions when they dissolve in water and therefore do not carry a current; they are NONelectrolytes. 21

Ionization vs. Dissociation Ionization is the formation of ions. Ionization occurs as the result of a chemical reaction of certain substances with water. Dissociation is when cations and anions separate from each other in the solvent. 22

Ionization vs. Dissociation Acetic acid ionizes and dissociates in water to form acetate ion and hydronium ion. It is a WEAK acid, so it is less than 10% dissociated. HC 2 H 3 O 2(aq) + H 2 O(l) ↔ H 3 O+(aq) + C 2 H 3 O 2 -(aq) HNO 3, a strong acid, is 100 % dissociated. HNO 3(aq) + H 2 O(l) → H 3 O+(aq) + NO 3 -(aq) 23

HCl 100% Strong ionized Acid Solution HC 21% H 3 Oionized 2 Weak Acid Solution 24 15. 3

STRONG ACID OR BASE VS. WEAK ACID OR BASE: Strong acid or base dissociates completely. Relative strengths: just memorize these SA: HCl, HNO 3, H 2 SO 4, (HCl. O 4, HBr, HI). WA: your other three acids plus all others, including all organic acids; dissociate < 10%. SB: any Group I or Group II hydroxide or oxide. WB: all others, including NH 3 and amines dissociate < 10%. 25

Practice with Electrolytes Classify the following as strong electrolytes, weak electrolytes or nonelectrolytes AND as strong or weak acids, strong or weak bases, salts or covalent solutes: H 2 SO 4, C 12 H 22 O 11, NH 3, K 2 SO 4, CH 3 CH 2 OH, HNO 3, Na. OH, Na. NO 3, HC 2 H 3 O 2, CH 3 NH 2 26

SELF-IONIZATION OF WATER: H 2 O(l) + H 2 O(l) H 3 O+(aq) + OH-(aq) Kw = [H 3 O+][OH-] = 1. 0 x 10 -14 at 25 o. C In pure water: [H 3 O+] = [OH-] = x Then Kw = x*x = 1. 0 x 10 -14 and therefore, x = 1. 0 x 10 -7 M = [H 3 O+] 27

THE p. H SCALE: A LOGARITHM SCALE OF [H 3 O+] p. Q = - log Q p. H = - log [H 3 O+] p. OH = - log [OH-] [H 3 O+] = 10 -p. H [OH-] = 10 -p. OH The number of decimal places of a logarithm is equal to the number of significant figures in the original number. Using logs: log (a*b) = log a + log b log ([H 3 O+][OH-]) = log [H 3 O+] + log [OH-] log (1. 0 x 10 -14) = log [H 3 O+] + log [OH-] -14 = (-p. H) + (-p. OH) 14 = p. H + p. OH (What is –log(nutbutter)? 28

THE p. H SCALE: A LOGARITHM SCALE OF [H 3 O+] The p. H scale is from 0. 00 to 14. 00 because of this. Scale was developed for dilute solutions, where p. H = -log[H 3 O+] <---inc acidity----neutral ------inc alkalinity---> |----|----|----|----|----|----|----| 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 0. 1. 01 10 -4 10 -7 10 -10 p. H of pure water is 7, meaning [H 3 O+] is 1. 0 x 10 -7. Then [OH-] is 1. 0 x 10 -7 and p. OH is 7 also. 29

TO FIND p. H OF A STRONG ACID OR STRONG BASE: DO A SOLUTION INVENTORY AND FIND [H 3 O+] OR [OH-]. THEN FIND p. H OR p. OH. Find p. H, p. OH and [OH-] for 1. 0 x 10 -3 M HCl(aq) + H 2 O(l) H 3 O+(aq) + Cl-(aq), therefore [H 3 O+] = 1. 0 x 10 -3 M p. H = - log (1. 0 x 10 -3 M) = 3. 00 14. 00 = 3. 00 + p. OH, p. OH = 11. 00 [OH-] = 10 -p. OH = 10 -11. 00 = 1. 00 x 10 -11 M 30

TO FIND p. H OF A STRONG ACID OR STRONG BASE: DO A SOLUTION INVENTORY AND FIND [H 3 O+] OR [OH-]. THEN FIND p. H OR p. OH. Noninteger p. H values: If [HCl] = 6. 0 x 10 -4 M, then so is [H 3 O+] p. H = - log (6. 0 x 10 -4 M) = 3. 22 What is p. OH? 14. 00 = 3. 22 + p. OH = 10. 78 31

TO FIND p. H OF A STRONG ACID OR STRONG BASE: DO A SOLUTION INVENTORY AND FIND [H 3 O+] OR [OH-]. THEN FIND p. H OR p. OH. A saturated solution of calcium hydroxide has [OH-] of 0. 025 M. What is its p. H? p. OH = - log(0. 025) = 1. 60 p. H + 1. 60 = 14. 00 p. H = 12. 40 32

The p. H scale of Acidity and Basicity 33 15. 4

p. H of Common Substances Substance p. H 1. 0 M HCl 0. 0 0. 1 M HCl 1. 0 stomach acid 1. 0 to 3. 0 lemons 2. 2 to 2. 4 soft drinks 2. 0 to 4. 0 plums 2. 8 to 3. 0 apples 2. 9 to 3. 3 cherries 3. 2 to 4. 0 unpolluted rainwater 5. 6 human blood 7. 3 to 7. 4 egg whites 7. 6 to 8. 0 milk of magnesia (sat’d Mg(OH)2) 10. 5 household ammonia 10. 5 to 11. 5 1. 0 M Na. OH 14 34

Acid-Base Stoichiometry Neutralization: acid-base reactions are analyzed by titration. This is volumetric analysis using a standardized solution to find mass or concentration of another substance. Titration: the process of measuring the volume of one reagent required to react with a measured mass or volume of another reagent. Burettes: contain the titrant, usually standardized. Flask: contains analyte, the substance we want to analyze. Endpoint: when the indicator changes color to say reaction is done. 35

Titration Use reaction stoichiometry to determine the concentration of an unknown solution. Titrant (unknown solution) added from a burette. Indicators are chemicals added to help determine when a reaction is complete. Endpoint of the titration occurs when the reaction is complete. 36

Titration: Actually, this is TOO PINK!!! 37

Titration: The base solution is the titrant in the buret. As the base is added to the acid, the H+ reacts with the OH– to form water. But there is still excess acid present so the color does not change. At the titration’s endpoint, just enough base has been added to neutralize all the acid. At this point the indicator changes color. 38

If 42. 00 m. L of 0. 150 M Na. OH solution is required to neutralize 50. 00 m. L of hydrochloric acid solution, then what is the molarity of the acid solution? The equation for the reaction is HCl(aq) + Na. OH(aq) → Na. Cl(aq) + H 2 O(l) acid base salt Calculate the liters of Na. OH that react. The unit of volume when Convert m. L of Na. OH to using molarity is liters of Na. OH Calculate the moles of Na. OH that react. 39

The moles of Na. OH that react equals the moles of HCl that react. 0. 00630 mol Na. OH react. 0. 00630 mol HCl react. The molarity of the HCl solution is 40

Buffers are solutions that resist changing p. H when small amounts of acid or base are added. They resist changing p. H by neutralizing added acid or base. Buffers are made by mixing together a weak acid and its conjugate base, or weak base and it conjugate acid. 41

How Buffers Work The weak acid present in the buffer mixture can neutralize added base. The conjugate base present in the buffer mixture can neutralize added acid. The net result is little to no change in the solution p. H. 42

A Buffer made from Acetic acid and Sodium Acetate A buffer solution with a p. H of 4. 75 can be made by mixing equal volumes of 1 M HC 2 H 3 O 2 and 1 M Na. C 2 H 3 O 2. Adding 10 m. L of 0. 1 M HCl to 1 L of this solution will give a solution with a p. H of 4. 75. Adding 10 m. L of 0. 1 M HCl to 1 L of distilled water will give a solution with p. H of 3. 0. Adding 10 m. L of 0. 1 M Na. OH to 1 L of this solution will give a solution with a p. H of 4. 75. Adding 10 m. L of 0. 1 M Na. OH to 1 L of distilled water will give a solution with p. H of 11. 0. 43

Acetic Acid/Acetate Buffer 44

45