Chapter 16 Acids -taste sour -can be strong or weak electrolytes -cause indicators to change color -can dissolve metals -can neutralize a base (will form salt and water when reacted with a base)

monoprotic acid- contains one ionizable H diprotic acid- contains two ionizable H triprotic acid- contains three ionizable H

Bases -taste bitter -slippery feeling -can be strong or weak electrolytes -can neutralize an acid (will form salt and water when reacted with an acid) -cause indicators to change color

Definitions of acids and bases Arrhenius Definition acid- a substance that produces H + ions in aqueous solution ex- HCℓ(aq)  H + (aq) + Cℓ - (aq) base- a substance that produces OH - (hydroxide) ions in aqueous solution ex- NaOH(aq)  Na + (aq) + OH - (aq) *these definitions have limitations

- Bronsted-Lowry Definition acid- proton (H + ion) donor ex HCℓ(aq) + H 2 O(ℓ)  H 3 O + (aq) + Cℓ - (aq) -produces hydronium ion- H 3 O + (H + ) *Pg. 653 base- proton (H + ion) acceptor -form OH - in solution ex NH 3 (aq) + H 2 O(ℓ)  NH 4 + (aq) + OH - (aq) *Pg. 654

-in Bronsted-Lowry definition, there will be an acid and a base in each reaction -some substances can act as an acid in one reaction and a base in another amphiprotic- substances that can both accept and donate a proton -when combined with something more acidic than itself it acts as a base -when combined with something more basic than itself it acts as an acid

conjugate acid-base pair- two substances related to each other by the transfer of a proton -an acid donates a proton and becomes a conjugate base -a base accepts a proton and becomes a conjugate acid

Sample Exercise 16.1 page 655 a)conjugate base of HCℓO 4, H 2 S, PH 4 +, HCO 3 - CℓO 4 -, HS -, PH 3, CO 3 -2 b) conjugate acid of CN -, SO 4 2-, H 2 O, HCO 3 - HCN, HSO 4 -, H 3 O +, H 2 CO 3 Practice Exercise H 2 SO 3, HF, HPO 4 2-, HCO +

Sample Problem 16.2 page 656 Write equation for reaction of hydrogen sulfite with water. a)ion acts as acid HSO H 2 O ⇌ SO H 3 O + b)ion acts as a base HSO H 2 O ⇌ H 2 SO 3 + OH - a)conj base = SO 3 -2 conj acid= H 3 O + b) conj base = OH - conj acid= H 2 SO 3

Acid Strength strong acid- completely ionizes in solution, completely transfers its protons to water -conj base shows negligible basicity

weak acid- only partially ionizes in solution -exists as a mixture of acid and conj base -conj base is a weak base

-a substance with negligible acidity contains H, but does not demonstrate any acidic behavior in water -conj base is a strong base

Proton-Transfer Reactions -governed by the ability of two bases to accept protons -if base in forward reaction is stronger than conj base, then equil lies to right (strong acid) -if conj base is stronger than base in forward, then equil lies to the left (weak acid) K c > 1  lies to rightK c < 1  lies to left *Page 657 Fig 16.3

Sample Exercise 16.3 page 658 HSO 4 - (aq)+ CO 3 2- (aq) ⇌ SO 4 2- (aq) +HCO 3 - (aq) acid base conj base conj a cid Which way does equil favor? * CO 3 2- is a stronger base than conj base (SO 4 2- ) so lies to right *K c >1

Practice Exercise page 658 a)favors left b/c conj base is stronger base b)favors right b/c stronger base on left side

Autoionization/Self-ionization of Water -the reaction in which two water molecules produce ions H 2 O(ℓ) + H 2 O(ℓ) ⇌ OH - (aq) + H 3 O + (aq) -water acts as both an acid and a base even with itself K w = ion product constant for water K w = [H + ][OH - ] = 1.0 x M 2 *at 25°C

neutral solution- [H + ] and [OH - ] are equal K w = [H + ] = [OH - ] = 1.0 x M acidic solution: [H + ] is greater than [OH - ] *[H + ] > 1.0 x M basic solution: [H + ] is less than [OH - ] *[H + ] < 1.0 x M *also known as alkaline solutions

Ex: Are these solutions acidic, basic or neutral? a)[H + ] = 4 x M basic b)[OH - ] = 1.4 x M basic c) [OH - ] = 7 x M acidic

Ex: Calculate [H + ] in: a)a solution in which [OH - ] is 0.100M K w = [H + ][OH - ] 1.0 x M 2 / 0.100M = [H + ] [H + ] = 1.0 x M *basic b)a solution in which [OH - ] = 1.8 x M 1.0 x M 2 / 1.8 x M = [H + ] [H + ] = 5.6 x M *acidic

*[H + ] can also be expressed using pH scale pH = power of hydrogen -ranges from 0-14 pH < 7 = acids 0= strongly acidic pH > 7 = bases14= strongly basic pH = 7 = neutral solution **based on scales of 10 pH = -log [H + ] pOH = -log [OH - ] pH + pOH = 14

Ex: Calculate pH of solutions with: a) [H + ] = 5.6 x M pH = -log 5.6 x M = 5.3 *acidic b) [OH - ] = 5.0 x M pOH = -log 5.0 x M = = 5.7 *acidic

-if you have the pH or pOH you can find the [H + ] or [OH - ] by using antilog [H + ] = antilog -pH [OH - ] = antilog -pOH antilog = 10 x on calculator Sample Exercise 16.7 page 662 Practice Exercise page 662 and 663

How to Measure pH -pH meters -acid-base indicators -litmus paper (acids  blue litmus paper will turn red, bases  red litmus paper will turn blue) -common indicators- page 664

Strong Acids and Bases -common strong acids = HCℓ, HBr, HI, HNO 3, HCℓO 3, HCℓO 4, H 2 SO 4 *all monoprotic acids: [H + ] = [solution] -common strong bases = alkali metal and alkaline earth metal hydroxides from Ca down *both are represented by a single arrow in the equation b/c they completely ionize

Ex: What is the pH of: a)0.028M solution of NaOH *only one OH - so [NaOH] = [OH - ] pOH = -log = = b)0.0011M solution of Ca(OH) 2 *2 OH - so [OH - ] = 2 x [Ca(OH) 2 ] = pOH = -log = = Practice Exercise page 665 and 666

Weak Acids -only partially ionize in solution (page 667) Ex: HA(aq) + H 2 O(l) ⇌ H 3 O + (aq) + A - (aq) HA(aq) ⇌ H + (aq) + A - (aq) -equilibrium expression: K a = [H + ][A - ] [HA] K a = acid-dissociation constant -the larger the K a value, the stronger the acid *K a for weak acids usually range from to

Polyprotic Acids -contain more than one ionizable H Ex: H 2 SO 3 (aq) ⇌ H + (aq) + HSO 3 - (aq) K a1 = 1.7 x HSO 3 - (aq) ⇌ H + (aq) + SO 3 2- (aq) K a2 = 6.4 x * K a2 is smaller b/c it is easier to remove first p+ b/c negative charge of anion causes p+ to be held more tightly Page 674 Table 16.3 *if K values differ by at least 10 3 then treat as monoprotic acid

Weak Bases -react with water, abstracting protons from water -have one or more lone pairs to form bond with H + Ex: B(aq) + H 2 O(l) ⇌ HB + (aq) + OH - (aq) B(aq) ⇌ HB + (aq) + OH - (aq) -equilibrium expression: K b = [HB + ][OH - ] [B] K b = base-dissociation constant -higher K b = more basic

Types of Weak Bases 1)neutral substances with lone pair of e- Ex- page 676 *most contain N (amines) 2)anions of weak acids Ex: NaCℓO (sodium hypochlorite) BLEACH -dissociates into Na + and CℓO - -Na + is spectator ion and CℓO - acts as weak base

-stronger acids have weaker conj bases -leads to: K a x K b = K w -as K a gets larger, K b must get smaller to remain at 1 x *only applies to conj acid-base pairs *can also be written as pK a + pK b = pK w = (-log K a or -log K b )

Examples: 1)Calculate the K b for the F - in HF if K a = 6.8x K b = 1.0 x /6.8 x = 1.5 x )Calculate the K a for the ammonium ion if K b = 1.8x K a = 1.0 x /1.8 x = 5.6 x Practice Exercise page 681

Acid-Base Properties of Salt Solutions -salts are strong electrolytes and properties are due to behavior of cations and anions *remember that the salt is the cation from the base and the anion from the acid hydrolysis- reaction with water, when a cation or anion reacts with water it changes pH

Anion’s Ability to React with Water -anions are conj bases of acids -if anion is the conj base of a strong acid, pH will not be altered b/c there will not be any OH - (neutral) -if anion is the conj base of a weak acid, it is a weak base and OH - will be produced to increase pH (basic)

Cation’s Ability to React with Water -cations are conj acids of bases -if cation is conj acid of weak base the cation is a weak acid and the pH will be lowered b/c H 3 O + is produced (acidic) -highly charged small metal cations (+3 or >) react with water to decrease pH (acidic) -ions of alkali metals and alkaline earth metals do not react with water- small and low charges-no pH change (neutral)

Ex:a, b, or n? 1)NO 3 - 2)NO 2 - 3)C 2 H 3 O 2 - 4)C 5 H 5 NH + 5)Ca 2+ 6) Cr 3+ neutral basic acidic neutral acidic basic

Combined Effect of Anion and Cation 1) if anion is CB of SA and cation is from Group 1A or 2A, pH is neutral 2) if anion is CB of WA and cation is from Group 1A or 2A, pH is basic 3) if anion is CB of SA and cation is CA of a WB or has charge of 3+ or greater, pH is acidic 4)if anion and cation from WA and WB must look at individual ions *need to compare K a and K b values