Acids and Bases Flashcards
Bronsted-Lowry Theory
- Focusses on the transfer of H+ during rxn
- Acids donate H+, bases accept (or proton)
Conjugate Pairs
- An acid can only donate if there is a base acceptor
- Conjugate pairs will only differ by one proton
ex. HA + B -> A- + BH+
HA acid -> A- base, B base -> BH+ acid
Amphiprotic Substances
- Acts like an acid or base
- For BL acid, must dissociate and release H+
- For BL base, must accept H+ and have a lp
Properties of Acid and Bases
Alkali: soluble base, usually releases OH-
Salt: Ionic compound formed when H+ is replaced with another positive ion
Types of Acid-Base Reactions
- Acid + Base -> Salt + H2O
- Metal + Acid -> Salt + H2
- Acid + Carbonate -> Salt +H2O + CO2
the pH scale
- Acidity or alkalinity related to concentration of H+ and OH- respectively
- pH = -log[H+], [H+] = 10^-pH, small number implies base
- Change in 1pH => change in [H+] x10, small pH change => large H+ change
Calculation involving Acids and Bases
- rare product of water
- ex. Kc = [H+] [OH-] /[H2O]
- [H2O] remains constants so,
[H2O] x Kc = [H+] [OH-]
Kw = [H+] [OH-] - Increase in temp favours right side, both [] increase, pH decreases
- Kw = -log[H+]
Concentrations in relation to pH
[H+] > [OH-] => acidic =. pH < 7
[H+] = [OH-] => neutral = ph=7
[H+] < [OH-] => basic = ph>7
pOH
- pOH = -log[OH-]
[OH-] = 10^-pOH - pKw = -log[OH-]
- pH and pOH are inversely related
Acid Deposition
- Acid Rain
- Rain typically is 5.6 pH, acid rain is less due to SO2 and N oxides
- Physical cleaning prior to combustion removes 80-90% of inorganic S
- CaO reacts with SO2 to remove it after combustion
pH curves
- Result of a titration, controlled neutralization
- Plot of pH v. V of added reactant
- Can be found using probes or calculations
1. Strong A + Strong B: equivalence point of 7
2. Weak A + Strong B : has a buffer, equivalence point greater than 7
3. Strong A + Weak B: buffer zone, equivalence point less than 7
4. Weak +Weak: buffer zone, approximately 7
Strong and Weak Acids
Strong: react almost completely, high conductivity, HCl, HNO3, H2SO4, HClO4
Weak: hardly reacts, low conductivity, a []ed weak A may have more H+ than a dilute strong acid
Strong and Weak Bases
Strong: react almost completely, high conductivity, Group 1 and 2 hydroxides
Weak: hardly reacts, low conductivity
Lewis Acids and Bases
Acids: e- pair acceptors
Bases: e- pair donors
- Lewis A-B rxns always result in both e- from a base
- Uses when something can only be described by Lewis
Transition metals and Ligands
Transition Metals: form ions with vacant d-sublevel orbitals, act as a lewis acid (electrophile)
Ligands: uses lp to form a dative bond with a metal ion, act as a lewis base (nucleophile)
Dissociation Constants
- Kc becomes Ka, acid dissociation constant, proportional to [H3O+]
- [H3O+] = [A-] (1:1)
- Kc becomes Kb, base dissociation constant, proportional to [OH-]
- [OH-] = [BH+]
pKa and pKb
- pKa = -logKa
- pKb = -logKb
- Inversely related
- Chnage in 1 pKa/b = 10x change in Ka/b
Kw calculations
- Ka x Kb = Kw
- -log(Ka x Kb) = -logKw
Buffers
- Aqueous solutions resistant to pH changes when a small amount of A/B is added
- Messes with equilibrium, shifts significantly in either direction
- [A-] = [HA]
- [BH+] = [B]
Preparing a Buffer
- Neutralize half of the weak A/B
- Adding a Conjugate salt
- Adding an acid: increase H3O+ (shift left) and decrease OH- (right), pH restored
- Adding a base: decrease H3O+(shift left) and increase OH- (right), pH restored
Salt Hydrolisis
Cation from base and anion from acid forming an ionic compound, 4 cases
1. Strong A and B = neutral salt , pH close to 7
2. Weak A and Strong B = basic salt, pH > 7
3. Strong A and Weak B = acidic salt, pH < 7
4. Weak A and B = depends but mostly neutral
