Ch. 10: Acids and Bases

Question 1

how does an Arrhenius acid behave

Answer 1

Arrhenius acids dissociate to form an excess of H+ in solution

Question 2

how does an Arrhenius base behave

Answer 2

Arrhenius base dissociate to form an excess of OH- in solution

Question 3

how does a Bronsted-Lowry acid behave

Answer 3

Bronsted-Lowry acids are PROTON (H+) donors

Question 4

how does a Bronsted-Lowry base behave

Answer 4

Bronsted-Lowry bases are PROTON (H+) acceptors

Question 5

how does a Lewis acid behave

Answer 5

Lewis acids are ELECTRON pair acceptors

Question 6

how does a Lewis base behave

Answer 6

Lewis bases are ELECTRON pair donors

Question 7

what is an amphoteric species? how does it behave?

Answer 7

reacts like…

• an acid in a basic environment (donating proton, accepting electron)
• a base in an acidic environment (acceptation proton, donating electron)

WATER

Question 8

how is water an amphoteric species

Answer 8

acts like an acid (donates proton) in a base
H2O + B- HB + OH-

acts like a base (accepts proton) in an acid
HA + H2O A- + H3O+

Question 9

what is an amphiprotic species

Answer 9

species that can either gain or lose a proton

Question 10

what occurs during autoionizations

Answer 10

amphoteric species react with themselves to yield basic AND acidic ions

H2O + H2O -OH + H3O+

Question 11

what is the water dissociation constant, Kw

Answer 11

Kw = [H3O+][OH-] = 10^-14 at 25C (298K)

when autoionizied, the concentrations of H3O+ and OH- will always equal 10^-14 at 25C

Question 12

what properties is Kw dependent on

Answer 12

like all equilibrium constants, Kw is dependent only on temperature. Changes to concentration, pressure, and volume will not effect Kw

Question 13

what do pH and pOH scales measure

Answer 13

the concentrations of H+ and -OH ions in concentration on a negative logarithmic scale

Question 14

what is the equation for the pH of a solution

Answer 14

pH = - log[H+] = log 1/[H+]

Question 15

what is the equation for the pOH of a solution

Answer 15

pOH = -log[-OH] = log 1/[-OH]

Question 16

what does pH + pOH =

Answer 16

pH + pOH = 14

as pH increases, pOH decreases by the same amount and vice versa

Question 17

what is the approximate pvalue for n * 10^-m

Answer 17

p value ~ m - 0.n

ex: Ka = 1.8 * 10^-5 … pKa ~ 5 - 0.18 ~ 4.82

Question 18

how are strong acids and bases different than weak acids and bases

Answer 18

strong acids/bases completely dissociate into their component ions in aqueous sol’ns

weak acid/bases partially dissociate into their component ions

Question 19

what does log 1 =

Answer 19

log 1 = 0

Question 20

what does log 10 =

Answer 20

log 10 = 1

Question 21

what is the equation for an acid dissociation constant, Ka

Answer 21

HA + H2O H3O+ + A-

Ka = [H3O+][A-] / [HA]

WATER IS PURE LIQUID, NOT INCLUDED

Question 22

what is the equation for a base dissociation constant, Kb

Answer 22

BOH B+ + -OH

Kb = [B+][OH-]/[BOH]

WATER IS PURE LIQUID, NOT INCLUDED

Question 23

what do Kb and Ka values less than one indicate

Answer 23

weak bases and acids

Question 24

what kind of acid-base reaction occurs in conjugate pairs

Answer 24

bronsted-lowry acid-base reaction

base + conjugate acid
acid + conjugate base

Question 25

what is a conjugate acid

Answer 25

acid formed when a BL base accepts a proton

Question 26

what is a conjugate base

Answer 26

base formed when a BL acid donates a proton

Question 27

equation for dissociation constants of conjugate pairs

Answer 27

Ka, acid * Kb, conjugate base = Kw = 10^-14 | Kb, base * Ka, conjugate acid = Kw = 10^-14

Question 28

how are Ka and Kb values related

Answer 28

inversely | when one value is high, the other value is low

Question 29

how do electronegative elements affect acid strength

Answer 29

* increases acidity* - electronegative substituents positioned near an acidic proton pull electron density out of the acidic bond - facilitates dissociation of the acidic hydrogen

Question 30

what occurs during a neutralization reaction

Answer 30

an acid and a base are reacted together to form a salt and water HA + BOH BA + H2O

Question 31

what occurs during a hydrolysis reaction

Answer 31

water and a salt are reacted together to form an acid and a base

Question 32

what is an acid equivalent equal to

Answer 32

one mole of H+ ions (H3O+)

Question 33

what is a base equivalent equal to

Answer 33

one mole of OH- ions

Question 34

what does it mean to be polyvalent/polyprotic

Answer 34

each mole of acid or base liberates more than one acid or base equivalent

Question 35

what is the purpose of titration

Answer 35

to determine the concentration of a known reaction in a solution

Question 36

how are titrations performed [big picture]

Answer 36

small volumes of a solution with known concentration [titrant] are added to a known volume of a solution with unknown concentration [titrand] until the complete of the reaction is achieved at an equivalence point

Question 37

when is the equivalence point reached in acid base titration

Answer 37

when the number of acidic equivalents present in the original solution equals the number of base equivalents added (or vice versa)

Question 38

what equation relates normalities with volumes for titrations

Answer 38

NaNb = VaVb where N is normality (equivalents added) and V is volume of the solutions

Question 39

what are indicators

Answer 39

weak acids or bases that have different colors in their protonate and deprotonated states binding/release of a proton --> change in absorption spectrum --> perceived change in color

Question 40

what occurs at the endpoint

Answer 40

the indicator changes to its final color

Question 41

what makes a particular indicator a good choice for a titration

Answer 41

- weak acid/base | - Kb or Ka is lower than what is being titrated

Question 42

where is the equivalence point for a strong acid/strong base titration

Answer 42

pH = 7

Question 43

where is the equivalence point for a weak acid/strong base titration

Answer 43

pH > 7 reaction between weak acid a strong base produces weak conjugate base and VERY weak conjugate acid --> greater concentration of [-OH] at equilibrium

Question 44

where is the equivalence point for a strong acid/weak base titation

Answer 44

pH < 7 rxn between strong acid and weak base produces weak conjugate acid and VERY weak conjugate base --> greater concentration of [H+] at equilibrium

Question 45

where is the equivalence point of a weak acid/weak base titration

Answer 45

near neutral pH both species will partially dissociate

Question 46

what is a half equivalence point

Answer 46

point on a titration curve where half of a given species has been protonated/deprotonated

Question 47

what is a buffer solution made of

Answer 47

a weak acid/base and its salt ex: acetic acid (CH3COOH) and sodium acetate (Ch3COO-Na+) ammonia (NH3) and ammonium chloride (NH4+Cl-)

Question 48

what is useful about a buffer

Answer 48

resist changes in pH when small amounts of acid/base are added to the solution and can neutralize additions of charged compounds

Question 49

equation for pH of a weak acid buffer solution

Answer 49

pH = pKa + log [A-] / [HA]

Question 50

equation for pOH of a weak base buffer solution

Answer 50

pOH = pKb + log [B+] / [BOH]

Question 51

what is the pH or pOH when [acid/base] = [conjugate]

Answer 51

log [1] = 0 so... - pH = pKa - pOH= pKb

Question 52

what is the buffering capacity and how does it change?

Answer 52

it is the ability to which the buffer system can resist changes in pH increase with higher concentration ratios of acid/base to conjugate and decreased with lower concentrations