1 Acids, Bases and Salts Some slides from: chemistrygeek.com

Acid and Bases

Naming of Acids H + and a nonmetal hydro (nonmetal) -ide + ic acid HCl (aq) = hydrochloric acid H+ & a polyatomic ion. (polyatomic ion) -ate +ic acid HNO 3 (aq) = nitric acid (polyatomic ion) -ide +ic acid HCN (aq) = cyanic acid (polyatomic ion) -ite +ous acid HNO 2 (aq) = nitrous acid

5 Acid Properties taste sour change the color of litmus from blue to red. blue to red a-cid. react with: –metals such as Zn & Mg (lower on activity series)to produce H 2 gas & a salt –hydroxide bases to produce water and an ionic compound (salt) –carbonates to produce carbon dioxide. HCl + CaCO 3  CaCl 2 + CO 2 + H 2 O These properties are due to the release of hydrogen ions, H +, in water solution.

Formula Writing of Acids: Review Write the H +1 first, then figure out what the negative ion is based on the name. Cancel out the charges to write the formula. Don’t forget the (aq) after it…it’s only an acid if it’s in water! Hydrosulfuric acid: H +1 and S -2 = H 2 S (aq) Carbonic acid: H +1 and CO 3 -2 = H 2 CO 3 (aq) Chlorous acid: H +1 and ClO 2 -1 = HClO 2 (aq) Hydrobromic acid: H +1 and Br -1 = HBr (aq) Hypochlorous acid: Perchloric acid:

Some Common Bases NaOHsodium hydroxidelye KOHpotassium hydroxideliquid soap Ba(OH) 2 barium hydroxidestabilizer for plastics Mg(OH) 2 magnesium hydroxide“MOM” Milk of magnesia Al(OH) 3 aluminum hydroxideMaalox (antacid) Al(OH) 3 aluminum hydroxideMaalox (antacid)

8 Base Properties Produce OH- in water bitter or chalky taste a slippery, soapy feeling: react with fats to form soap & glycerol (glycerine). change litmus red to blue: “basic blue” interact with acids (neutralize acids). Form when group I & II metals react with water. The word alkali & alkaline means basic.

Naming of Bases Bases are named like any ionic compound, the name of the metal ion first (with a Roman numeral if necessary) followed by “hydroxide”. Fe(OH) 2 (aq) = iron (II) hydroxide Fe(OH) 3 (aq) = iron (III) hydroxide Al(OH) 3 (aq) = aluminum hydroxide NH 3 (aq) is the same thing as NH 4 OH: NH 3 + H 2 O  NH 4 OH Also called ammonium hydroxide.

Formula Writing of Bases Formula writing of bases is the same as for any ionic formula writing. The charges of the ions have to cancel out. Calcium hydroxide = Ca +2 and OH -1 = Ca(OH) 2 (aq) Potassium hydroxide = K +1 and OH -1 = KOH (aq) Lead (II) hydroxide = Pb +2 and OH -1 = Pb(OH) 2 (aq) Lead (IV) hydroxide = Pb +4 and OH -1 = Pb(OH) 4 (aq) Lithium hydroxide = Copper (II) hydroxide = Magnesium hydroxide =

11 Arrhenius Acid/Base Definition Svante Arrhenius( )was a Swedish scientist An Acid is a hydrogen-containing substance that dissociates to produce hydrogen ions (or hydronium ions, H3O + ) in water.” An Arrhenius base is a hydroxide-containing substance that dissociates to produce hydroxide ions in aqueous solution. HA → H + + A - MOH → M + (aq) + OH - (aq)

Arrhenius acid is a substance that produces H + (H 3 O + ) in water Arrhenius base is a substance that produces OH - in water

13 Bronsted and Lowry Definition J.N. Bronsted ( ) and T. M. Lowry ( ) advanced theory of acids and bases. Acids – proton donor Bases – proton acceptor A “proton” is really just a hydrogen atom that has lost it’s electron!

14 HCl (aq) + H 2 O(l) → H 3 O + (aq) + Cl - (aq) proton acceptor Bronsted-Lowry Base proton donor Bronsted-Lowry Acid

A Brønsted-Lowry acid is a proton donor A Brønsted-Lowry base is a proton acceptor acid conjugate base base conjugate acid Conjugate acid-base pairs differ by a single proton.

ACID-BASE THEORIES The Brønsted definition means NH 3 is a BASE in water — and water is itself an ACID

Conjugate Pairs

Label the acid, base, conjugate acid, and conjugate base in each reaction: HCl + OH -  Cl - + H 2 O H 2 O + H 2 SO 4  HSO H 3 O +

19 1. Are sulphate and sulfuric acid conjugate acid and base of each other? Why or why not? 2. Write conjugate base of H 3 PO Write conjugate acid of NO 3 -

20 Lewis Acids and Bases G. N. Lewis (1923) developed a more comprehensive theory of acids and bases. Deals with the way in which a substance with an unshared pair of electrons reacts in an acid-base type of reaction.

Lewis Acids & Bases Lewis acid - a substance that accepts an electron pair ( has a vacant orbital) Lewis base - a substance that donates an electron pair

22 Lewis Acid Electron Pair Acceptor Lewis Base Electron Pair Donor Electron pair donated to H + Species that act as Lewis bases are also are also B-L bases (can accept H+). Lewis acids need not be B-L acids,broadens definition of acid.

Formation of hydronium ion is also an excellent example. Lewis Acids & Bases Electron pair of the new O-H bond originates on the Lewis base.Electron pair of the new O-H bond originates on the Lewis base.

Lewis Acid-Base Interactions in Biology The heme group in hemoglobin can interact with O 2 and CO.The heme group in hemoglobin can interact with O 2 and CO. The Fe ion in hemoglobin is a Lewis acidThe Fe ion in hemoglobin is a Lewis acid O 2 and CO can act as Lewis basesO 2 and CO can act as Lewis bases Heme group

Identify the lewis acid &base Ni NH 3  Ni(NH 3 )6 Cation can accept electrons Nitrogen has lone pair

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Strong and Weak Acids/Bases The strength of an acid (or base) is determined by the amount of IONIZATION. Acids and bases are generally divided into STRONG or WEAK ones.

Strong and Weak Acids/Bases STRONG ACID: HNO 3 (aq) + H 2 O (l) ---> H 3 O + (aq) + NO 3 - (aq) HNO 3 is about 100% dissociated in water. Weak acids are much less than 100% ionized in water. One of the best known is acetic acid, CH 3 CO 2 H

Strong Base: 100% dissociated in water.Strong Base: 100% dissociated in water. NaOH (aq) ---> Na + (aq) + OH - (aq) NaOH (aq) ---> Na + (aq) + OH - (aq) Strong and Weak Acids/Bases Other common strong bases include KOH and Ca(OH) 2. CaO + H 2 O -->Ca(OH) 2 CaO

Weak base: less than 100% ionized in waterWeak base: less than 100% ionized in water One of the best known weak bases is ammonia NH 3 (aq) + H 2 O(l)  NH 4 + (aq) + OH - (aq) Strong and Weak Acids/Bases

Weak Bases

32 A strong acid has a weak conjugate base & vice versa. List of strong Acids: HCl, HNO 3, H 2 SO 4, HI, HBr,, HClO 4 List of Strong Bases: group 1 metals (except Fr) and Sr, Ba, Ca hydroxides ( remember solubility rules) Monoprotic Acids: Have one proton that can be donated. Ex. HCl, HNO 3, H C 2 H 3 O 2 Diprotic Acids: Have two protons that can be donated. H 2 SO 4 Polyprotic Acids: Have more than two protons that can be donated. Ex. H 3 PO 4

Strong vs Weak Acids Ionize completely, forming H+ ions & anions. HCl (aq)  H+ (aq) + Cl- (aq) In 0.1 mol of HCl in water, there is 0.1 mol of H+ ions, 0.1 mol Cl- ions & no HCl. All acids that are not strong acids are weak acids: only partially ionized to H+ ions in water. HF (aq)  H+ (aq) + F- (aq) ( double arrow means does not go to completion) In 0.1 mol of HF in water, there is 0.01 mol of H + ions, 0.01 mol of F- ions & 0.09 mol of HF molecules. 33

34 HBr(aq) + KOH(aq) → KBr(aq) + H 2 O(l) 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: 2HNO 3 (aq) + Ca(OH) 2 (aq) → Ca(NO 3 ) 2 (aq) + 2H 2 O(l) acidbasesalt acidbasesalt

35 titration: The process of measuring the volume of one reagent required to react with a measured mass or volume of another reagent.

TitrationTitration 1. Add solution from the buret. 2. Reagent (base) reacts with compound (acid) in solution in the flask. 3.Indicator shows when exact stoichiometric reaction has occurred. (Acid = Base) This is called NEUTRALIZATION. This is called NEUTRALIZATION.

Setup for titrating an acid with a base

mL of M NaOH solution is required to neutralize mL of hydrochloric acid solution. What is the molarity of the acid solution? The equation for the reaction is HCl(aq) + NaOH(aq) → NaCl(aq) + H 2 O(l) acidbasesalt Convert mL of NaOH to liters of NaOH The unit of volume when using molarity is liters. Calculate the moles of NaOH that react. Calculate the liters of NaOH that react.

mL of M NaOH solution is required to neutralize mL of hydrochloric acid solution. What is the molarity of the acid solution? The equation for the reaction is HCl(aq) + NaOH(aq) → NaCl(aq) + H 2 O(l) acidbasesalt The mole ratio of HCl to NaOH is 1:1The moles of NaOH that react equals the moles of HCl that react mol NaOH react mol HCl react. The molarity of the HCl solution is.0126 M

40 (H + + Cl - ) + (K + + OH - ) → K + + Cl - + H 2 O In the total ionic equation all ions present in solution are written. H + (aq) + OH - (aq) → H 2 O(l) In the net ionic equation only the ions that react are written. HCl(aq) + KOH(aq) → KCl(aq) + H 2 O(l) acidbasesalt In the un-ionized equation all compounds are written using their molecular or formula expressions. K + ion does not react.Cl - ion does not react. Ions that do not participate in a chemical reaction are called spectator ions.

35.62 mL of NaOH is neutralized with 25.2 mL of M HCl by titration to an equivalence point. What is the concentration of the NaOH? mL of NaOH is neutralized with 25.2 mL of M HCl by titration to an equivalence point. What is the concentration of the NaOH? LAB PROBLEM #1: Standardize a solution of NaOH — i.e., accurately determine its concentration.

PROBLEM: You have 50.0 mL of 3.0 M NaOH and you want 0.50 M NaOH. What do you do? Dilute the solution. But how much water do we add?

PROBLEM: You have 50.0 mL of 3.0 M NaOH and you want 0.50 M NaOH. What do you do ? How much water is added? The important point is that ---> moles of NaOH in ORIGINAL solution = moles of NaOH in FINAL solution moles of NaOH in FINAL solution

moles of NaOH in ORIGINAL solution = moles of NaOH in FINAL solution Amount of NaOH in original solution = M V = (3.0 mol/L)(0.050 L) = 0.15 mol NaOH Amount of NaOH in final solution must also = 0.15 mol NaOH Volume of final solution = (0.15 mol NaOH) / (0.50 M) = 0.30 L or 300 mL M 1 V 1 = M 2 V 2

The pH scale is a way of expressing the strength of acids and bases. Instead of using very small numbers, we just use the NEGATIVE power of 10 on the Molarity of the H + (or OH - ) ion. Under 7 = acid 7 = neutral Over 7 = base

pH A change of 1 in pH is a tenfold increase in acid or base strength. A pH of 4 is 10 times more acidic than a pH of 5. A pH of 12 is 100 times more basic than a pH of 10.

47 The pH Scale The pH of a solution is defined as the negative of the common logarithm of the hydronium ion concentration. pH= -log [H 3 O + ] The pOH of a solution is defined as the negative of the common logarithm of the hydroxide ion concentration. pOH= -log[OH - ] [H 3 O + ] 1.0 Increasing acidity 1.0x10 -7 Increasing basicity 1.0x10 -14

48 pH = -log[H + ] [H + ] = 1 x when this number is exactly 1 pH = this number without the minus sign. pH = 5.0

49 pH = -log[H + ] [H + ] = 2 x when this number is between 1 and 10 The number of decimal places of a logarithm is equal to the number of significant figures in the original number. pH is between this number and next lower number (4 and 5). one decimal place one significant figure ph = 4.7

50 What is the pH of a solution with an [H + ] of 1.0 x ? pH = - log(1.0 x ) pH = decimal places 2 significant figures

51 What is the pH of M HCl? [H + ] = 2 x pH = - log( 2 x ) pH = 2.7

pH calculations – Solving for H+ If the pH of Coke is 3.12, [H + ] = ??? Because pH = - log [H + ], - pH = log [H + ] Take antilog (10 x ) of both sides and get 10 -pH = [H + ] [H + ] = = 7.6 x M *** to find antilog on your calculator, look *** to find antilog on your calculator, look for “Shift” or “2 nd function” and then the log button

pH calculations – Solving for H+ A solution has a pH of 8.5. What is the Molarity of hydrogen ions in the solution?A solution has a pH of 8.5. What is the Molarity of hydrogen ions in the solution? pH = - log [H + ] 8.5 = - log [H + ] -8.5 = log [H + ] Antilog -8.5 = antilog (log [H + ]) = [H + ] 3 X = [H + ] pH = - log [H + ] 8.5 = - log [H + ] -8.5 = log [H + ] Antilog -8.5 = antilog (log [H + ]) = [H + ] 3 X = [H + ]

54 Autoionization:Water ionizes slightly. baseacid base H 2 O + H 2 O → H 3 O + + OH - → → hydronium ion hydroxide ion Water ionization equilibrium can be expressed more simply as: Kw= [H 3 O + ] [OH - ] = 1.0 x mol/L (This expression can be used to calculate H+ or OH-) [H 3 O + ] or [H + ]= [OH-] = 1.0 x mol/L What is [OH-], if [H+] is 3.0 x ? ( ans: 3.3 X 10 –12 ) Two out of every 1 billion water molecules are ionized.

pOH Since acids and bases are opposites, pH and pOH are opposites!Since acids and bases are opposites, pH and pOH are opposites! pOH does not really exist, but it is useful for changing bases to pH.pOH does not really exist, but it is useful for changing bases to pH. pOH looks at the perspective of a basepOH looks at the perspective of a base pOH = - log [OH - ] Since pH and pOH are on opposite ends, pH + pOH = 14

56 H+ OH- pH pOH [H+] = 1.0 X 10 ^-14/ [OH-] [OH-] = 1.0 X 10 ^-14/ [H+] pOH= -log [OH-] [OH-]= 10^-pOH pH= -log [H+] [H+]= 10^-pH pH= 14- pOH pOH= 14- pH pH BOX

57 1. What is the pH of M NaOH? 2. What is [H+], if pH is 3.4? [OH - ] = 3 x pOH = - log( 3 x ) pOH = = = 4 X 10 -4

The pH of rainwater collected in a certain region of the northeastern United States on a particular day was What is the H + ion concentration of the rainwater? The OH - ion concentration of a blood sample is 2.5 x M. What is the pH of the blood?

59 The pH of rainwater collected in a certain region of the northeastern United States on a particular day was What is the H + ion concentration of the rainwater? pH = 4.82 [H+] = antilog = 1.5 X The OH - ion concentration of a blood sample is 2.5 x M. What is the pH of the blood? [OH-] = 2.5 X pOH = 6.6 pH = 7.40

Calculating [H 3 O + ], pH, [OH - ], and pOH Problem 1: A chemist dilutes concentrated hydrochloric acid to make two solutions: (a) 3.0 M and (b) M. Calculate the [H 3 O + ], pH, [OH - ], and pOH of the two solutions at 25°C. Problem 2: What is the [H 3 O + ], [OH - ], and pOH of a solution with pH = 3.67? Is this an acid, base, or neutral? Problem 3: Problem #2 with pH = 8.05?

61 Problem 1: A chemist dilutes concentrated hydrochloric acid to make two solutions: (a) 3.0 M and (b) M. Calculate the [H 3 O + ], pH, [OH - ], and pOH of the two solutions at 25°C. [H 3 O + ],= 3.0 M pH= -.48, [OH - ]=3.3 X , and pOH= [H 3 O + ],= 2.4 X M pH= 2.62, [OH - ]=4.2 X , and pOH= Problem 2: What is the [H 3 O + ], [OH - ], and pOH of a solution with pH = 3.67? Is this an acid, base, or neutral? H 3 O + ],= 2.1 X M, [OH - ]=4.8 X , and pOH= Acidic Problem 3: Problem #2 with pH = 8.05? H 3 O + ],= 9.0 X M, [OH - ]=1.1 X 10 -6, and pOH= 5.95 basic

Equilibria Involving Weak Acids & Bases Consider acetic acid, HC 2 H 3 O 2 HC 2 H 3 O 2 + H 2 O  H 3 O + + C 2 H 3 O 2 - Acid Conj. base (K is designated K a for ACID) K gives the ratio of ions (split up) to molecules (don’t split up) when an H+ is removed to form conj. Base.

Ionization Constants for Acids/Bases Acids ConjugateBases Increase strength

Equilibrium Constants for Weak Acids Weak acid has K a < 1 Leads to small [H 3 O + ] and a pH of 2 – 7 Water not included because concentration pretty much stays the same even though plays role in causing acid to ionize

Equilibrium Constants for Weak Bases Weak base has K b < 1 Leads to small [OH - ] and a pH of

Write the dissociation (ionization) reaction and Ka (omitting water) for each of the following A. Hydrochloric Acid B. Ammonium ion C. C 6 H 5 NH 3 + (anilinium ion) D. Sulfuric Acid 66

67 The Strength of an acid is defined by the equilibrium position of its dissociation reaction. A strong acid: one for which the equilibrium lies far to the right. Almost all acid is dissociated (ionized). A strong acid yields a weak conjugate base, weaker than water (one that has a low affinity for a proton) A weak acid: one for which the equilibrium lies far to the left. Most of the acid originally placed in the solution is still present as HA at equilibrium. A weak acid has a conjugate base that is stronger than water.

68 Compare the strengths of two acids in the following reactions. What does the strength of acid have to do with the direction in which this reaction occurs? (Forward reaction is favored, why?) Base 1 Acid 1 HCl(g)+ → Cl - (aq)+H 3 O + (aq)H 2 O (l) Acid 2 Base 2 If strong acid will completely ionize

69 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). Chemists use the terms ionic compound and salt interchangeably. Salts are usually crystalline and have high melting and boiling points.

70 NaOHHCl NaCl base acid salt The positive ion of the salt is derived from the base. The negative ion of the salt is derived from the acid. Salt Formation