10. Acids and Bases Flashcards
Bronsted-Lowry acid/base vs Lewis acid/base vs Arrhenius acid/base
Proton donor/proton acceptor vs vs e- pair acceptor/e- pair donor vs dissociating to make more H30+/dissociating to make more OH-
FYI: ALL ARRHENIUS ACIDS/BASES => B-L ACIDS/BASES => LEWIS ACIDS/BASES BUT NOT ALWAYS THE REVERSE
What does amphoteric vs amphiprotic mean?
Having both acid and base properties vs can either lose or gain a p+ in Bronsted-Lowry sense
What is autoionization?
When H2O reacts with itself: H2O can react with another H2O to produce H3O+ or OH-. Both H2O and OH- act as B-L bases
Take autoionization into account when finding pH of strong acids/bases —> conc could be 10x less
How to calculate pH vs pOH?
-log[H+] = 1/log[H+] vs -log[OH-] = 1/[OH-]
What’s the relationship b/w Kw and Ka/Kb, pKa/pKb, and pH/pOH?
Ka * Kb = Kw = 1E-14 = [H3O+][OH-]
pKa + pKb = 14; pH + pOH = 14
Know the Hendersen-Hasselbach eqn. What is this used for?
pH = pKa + log[A-]/[HA]; buffer slns
When do you use ice tables?
Finding pHs of weak acids/bases, common ion effect and buffer solns (buffer problems don’t have x’s as changes)
Titrant vs titrand
liquid with known conc that’s added slowly to titrand vs liquid with known vol but unknown conc
Half-equivalence point vs equivalence point
midpoint of buffering region in which half of titrant has been de/protonated thus [HA] = [A-]; pH = pKa vs steepest slope of titration curve, soln = neutralized (you got H2O and salt) –> where conjugate base of the weak acid predominates here; indicator changes color
At what pH is the equivalence point for SA/SB, WA/SB and WB/SA?
7, >7, <7
Ex of strong acids vs weak acids. What does it mean to be weak or strong?
HCl, HBr, HI vs chlorous acid (HClO2), HF, acetic acid, NH4+. if Ka > 10^-7 –> acidic
Weak or strong depends on how much acid = willing to dissociate (ie. if ratio of acid to conjugate base will be >/< 1). Strong acids would have a conjugate base that could stabilize neg charge after being deprotonated
Ex of strong bases vs weak bases. What does it mean to be weak or strong?
NaOH, KOH, Ca(OH)2, Mg(OH)2 vs NH3, amines, pyridine. if Ka < 10^-7 –> basic
Weak or strong depends on how much base = willing to dissociate (ie. if ratio of base to conjugate acid will be >/< 1)
pH >/< pKa meaning
pH < pKa –> exist in protonated form
pH > pKa –> exist in deprotonated form
Will weak bases react with H2O?
nope (so watch out if any cmpds dissolve into a weak base)
How to find pH from titration of strong acids/bases
not yet added: straight up find pH
little added: convert to mol –> mol ICE –> find new conc –> pH
more added: convert to mol –> mol ICE –> mol cancel? => neutralization
most added: convert to mol –> mol ICE –> find new conc –> pOH
How to find pH from titration of weak acid/strong base and weak base/strong acid
not yet added: nml ICE w/ weak acid sitting in H2O –> find pH
little added: convert to mol –> mol ICE w/ rxn –> find new conc –> usually H-H eqn –> find pH
more added: convert to mol –> mol ICE –> find new conc –> nml ICE w/ H2O –> pH
most added: convert to mol –> substract from neutralized mol –> pH
How to change equil constants?
Change temp and/or identity of slns
Kw (like all other equil constants) is only DEPENDENT ON TEMP! NOT PRESSURE, VOL, OR CONC
Kw inc when temp inc (ie. Above 298 K) cuz of endothermic nature
How to quickly convert conc into pH’s and pKa’s
Take exponent: [H+]=1E-3 —> pH=3, Ka=1E-12 —> pKa=12
Or
p[] = Exponent - 0.whole#
Dissociation eqns for weak acids vs bases
HA + H2O <=> H3O+ + A-
vs
BOH <=> B+ + OH- or B + H2O <=> HB+ + OH-
Neutralization rxn
When acid reacts with base to give salt and water. Reverse = hydrolysis
Acid equivalent vs base equivalent vs polyvalent
1 mol H+ vs 1 mol OH- vs acids and bases yield more than 1 acid or base equivalent (aka polypeptide under Bronsted Lowry sense)
Gram equivalent weight
Molar mass/n
n = # of target particles produced or consumed in a rxn (ex: you need 31 g of H2CO3 (molar mass=62 g) to make 1 equivalent of H ions cuz each H2CO3 gives 2 H ions
Normality (N)
Measure of conc expressed in equivalents/L; usually done for [H+]. Ex: 1 N HCl = 1 M HCl cuz there’s 1 H ion, 1 N H2CO3 = 0.5 M H2CO3 cuz there’s 2 H ions
molarity = normality/n where n=# of p+, e-, or ions produced or consumed by solute
Buffer slns vs buffering capacity
Mixture of weak acid/base with its salt (ex: CH3COOH & NaCH3COO, NH3 & NH4Cl) vs ability to which system can resist pH changes
Equivalence point eqn for strong acids + strong bases
N1V1=N2V2 or n1M1V1 = n2M2V2 where n = mol, like mol H and mol OH; crucial for equivalence point
Potentiometric titration
Form of redox titration in which an indicator is isn’t used —> use voltage instead
How to write Ka or Kb equil expressions
1) set up equilibrium dissociation eqn (HA + H2O <=> etc)
2) [prod]/[react] = Ka
basically the same as writing any other equil expression
How to find percent dissociation?
([A-]/[HA]) * 100
All strong acids have weak conjugate bases and everything vice versa. But weak acids have what strength conjugate bases?
weak conjugate bases
Do acid/base equilbria favor strong acid/base pair or weak acid/base pair?
weak acid/base pair
Acidity and basicity trend on periodic table
acidity inc right and down, basicity dec right b/c higher electroneg means atoms won’t want to donate their e- and down b/c inc atomic radius means dec basicity (size trumps electroneg)
Why does H3PO4 make a good buffer?
b/c it has 3 H to get rid off –> their pKas = across the entire pH scale
What happens if you add a strong acid to a sln of weak acid?
weak acid won’t ionize as much
How do halogens inc acidity?
if same halogen: alpha position = more acidic than beta, which = more acidic than gamma, etc; also, more halogens bonded –> the greater acidity. if diff halogens: F > Cl > Br > I
