Ch 10 - Acids and Bases

Question 1

What are arrhenius acids?

Answer 1

dissociate to produce an excess of hydrogen ions in solution

Question 2

What are arrhenius bases?

Answer 2

dissociate to produce an excess of hydroxide ions in solution

Question 3

What are Bronsted-Lowry acids/bases?

Answer 3

• acids: species that can donate hydrogen ions
• bases: species that can accept hydrogen ions
  revolves around protons

Question 4

What are Lewis acids/bases?

Answer 4

• acids: electron pair acceptors
• bases: electron pair donors
  revolves around electrons

Question 5

How do arrhenius, Bronsted-Lowry, and Lewis acids and bases compare?

Answer 5

• all Arrhenius acids and bases are Bronsted-Lowry acids and bases, and all Bronsted-Lowry acids and bases are Lewis acids and bases
• however, the reverse is not necessarily true
• not all Lewis are Bronsted and not all Bronsted are Arrhenius

Question 6

What is the difference between amphoteric and amphiprotic?

Answer 6

• amphoteric: can behave as an acid or base
• amphiprotic: amphoteric species that specifically can behave as a Bronsted acid/base
• water, amino acids, and partially deprotonated polyprotic acids such as bicarbonate and bisulfate are common examples of both
• metal oxides and hydroxides are amphoteric by not amphiprotic (do not give off protons)

Question 7

Why is water special in acid/bases?

Answer 7

• classic example of an amphoteric, amphiprotic species

- it can accept a hydrogen ion to become hydronium ion or it can donate a hydrogen ion to become a hydroxide ion

Question 8

What is the water dissociation constant (Kw)?

Answer 8

Kw = [H3O+][OH-] = 10^-14 at 298 K
Kw = Ka x Kb
- only affected by changes in temperature, in turn, change the significance of the pH scale

Question 9

How are pH and pOH calculated?

Answer 9

can be calculated given the concentrations of H3O+ and OH- ions
pH = -log[H+] = log(1/[H+])
pOH = -log[OH-] = log (1/[OH-])
- in aqueous solution, pH + pOH = 14

Question 10

What is the difference between strong and weak acids/bases?

Answer 10

• strong completely dissociate in solution

- weak do not completely dissociate in solution and have corresponding dissociation constants (Ka and Kb)

Question 11

What are the conjugates in Bronsted-Lowry acids/bases?

Answer 11

• acids have conjugate bases that are formed when the acid is deprotonated
• bases have conjugate acids that are formed when the base is protonated
• strong acids/bases have very weak (inert) conjugates
• weak acids/bases have weak conjugates
• removing a proton from a molecule produces the conjugate base and adding a proton produces the conjugate acid

Question 12

What do neutralization reactions form?

Answer 12

salts and (sometimes) water
HA + BOH --> BA + H2O

Question 13

What is an equivalent?

Answer 13

one mole of the species of interest

Question 14

What is normality in acid-base chemistry?

Answer 14

the concentration of acid or base equivalents in solution

Question 15

What are polyvalent acids/bases?

Answer 15

• those that can donate or accept multiple electrons
• the normality of a solution containing a polyvalent species is the molarity of the acid or base times the number of protons it can donate or accept

Question 16

What are titrations used for?

Answer 16

to determine the concentration of a known reactant in a solution

Question 17

What is a titrant and a titrand?

Answer 17

• titrant: has a known concentration and is added slowly to the titrand to reach the equivalence point
• titrand: an unknown concentration but a known volume

Question 18

What is the half-equivalence point?

Answer 18

the midpoint of the buffering region, in which half of the titrant has been protonated (or deprotonated); thus, [HA] = [A-] and a buffer is formed

Question 19

What is the equivalent point?

Answer 19

• indicated by the steepest slope in a titration curve
• reached when the number of acid equivalents in the original solution equals the number of base equivalents added or vice versa

Question 20

What are the pH of equivalent points of strong/weak acids/bases titrations?

Answer 20

• strong acids and strong base titrations have equivalence points at pH=7
• weak acid and strong base titrations have equivalence points at pH>7
• strong acid and weak base titrations have equivalence points at pH<7
• weak acid and weak base titrations can have equivalence points above or below 7, depending on the relative strength of the acid and base

Question 21

What are indicators?

Answer 21

weak acids or bases that display different colors in the protonated and deprotonated forms
- the indicator chosen for a titration should have a pKa close to the pH of the expected equivalent point

Question 22

What is the endpoint of a titration?

Answer 22

when the indicator reaches its final color

Question 23

What are buffer solutions?

Answer 23

consist of a mixture of a weak acid and its conjugate sat or weak base and its conjugate salt
- they resist large fluctuations in pH

Question 24

What is buffering capacity?

Answer 24

the ability of a buffer to resist changes in pH

- maximal buffering capacity is seen within 1 pH point of the pKa of the acid in the buffer solution

Question 25

What is Henderson-Hasselbalch equation?

Answer 25

quantifies the relationship between pH and pKa for weak acids and between pOH and pKb for weak bases
- when a solution is optimally buffered, pH - pKa and pOH = pKb
pH = pKa + log[A-]/[HA]
pOH = pKb + log[B+]/[BOH]

Question 26

What is the nomenclature for acids?

Answer 26

• most acids related to parent anion end in -ide
  F- fluoride, Cl- chloride, Br- bromide
• acids formed from anions have prefix hydro- and end in -ic
  HF hydrofluoric acid, HCl hydrochloric acid, HBr hydrobromic acid

Question 27

What are the common acids from -1 charged polyatomic ions?

Answer 27

ClO- hypochlorite; HClO hypochlorous acid
ClO2- chlorite; HClO2 chlorous acid
ClO3- chlorate; HClO3 chloric acid
ClO4- perchlorate; HClO4 perchloric acid
NO2- nitrite; HNO2 nitrous acid
NO3- nitrate; HNO3 nitric acid
CH3COO- acetate; CH3COOH acetic acid

Question 28

What are the common acids from -2 charged polyatomic ions?

Answer 28

CO3 2- carbonate; H3CO3 carbonic acid
SO4 2- sulfate; H2SO4 sulfuric acid
CrO4 2- chromate; H2CrO4 chromic acid

Question 29

What are the common acids from -3 charged polyatomic ions?

Answer 29

PO4 3- phosphate; H3PO4 phosphoric acid

BP3 3- borate; H3BO3 boric acid

Question 30

How are the acid/base dissociation constants calculated?

Answer 30

HA + H2O H3O+ + A-
Ka = [H3O+][A-]/[HA]
BOH B+ + OH-
Kb = [B+][OH-]/[BOH]

Question 31

How can the unknown concentration of a titrand be calculated?

Answer 31

NaVa = NbVb
Na and Nb are the acid and base normalities
Va and Vb are the volumes of the acid and base solutions

Question 32

How can Le Chatelier’s principle be applied to indicators?

Answer 32

indicators change color as they shift between their conjugate acid and base forms:
H - indicator1 H+ + indicator-2
adding H+ shifts the equilibrium to the lect
adding OH= removes H+ and therefore shifts the equilibrium to the right

Question 33

What is the function of a buffer?

Answer 33

resist change in pH when small amounts of acid or base are added

Question 34

Where are pKa values found on titration curves?

Answer 34

midpoint between the start and the equivalence points

Question 35

What is gram equivalent weight?

Answer 35

the weight (in grams) that releases 1 acid or base equivalent from a compounds

Question 36

How do Ka values relate to pH values?

Answer 36

• a higher Ka implies a stronger acid
• weak acids usually have a Ka that is several orders of magnitude below 1
• the pKa of a compound is the pH at which there are equal concentrations of acid and conjugate base
  pKa = -logKa

Question 37

How is the p scale approximation used?

Answer 37

p value `= M - 0.n

where 0.n is the sliding decimal point of n one position to the left (n/10)