Exam 2 Flashcards
conjugate base
species that remains when a proton has been removed from an acid
Conjugate acid
species that forms when attaches to a base
Arrhenius and bronsted lowry acid/base definitions
Arrhenius: Acids yield H+ and bases yield OH-
Bronsted-lowry: acids donate H+ and bases accept H+
Relationship between Kw and temp
direct
Formula for how many times faster a reaction is with a catalyst or for change in Ea
ln(k1/k2)=(Ea1-Ea2)/RT
How is pH of polyprotic acids determined?
The Ka of the first step determines the pH except for H2SO4.
For H2SO4: Write the first step and use stoichiometry to calculate the initial concentrations of HSO4-, then plug those into an ice table for the second step of the dissociation. Solve for x using quadratic formula for Ka2
degree of ionization
d=|H+| / |HA|i
Factors affecting acid strength
- Oxygen’s bonded to central atom: O bonded to the central atom draw electron density towards themselves. More electron density drawn away from O-H groups=more delocalized negative charge the anion formed when H+ is lost, more O=stronger
- Higher oxidation number of central atom=stronger acid
- Higher electronegativity of halogen atom=stronger
Exception to acid strength trends
H3PO4 is not stronger than H3PO3 because H3PO3 is diprotic
how do qualitatively determine pH of salts of weak acids and bases
- pKa=pKa: neutral
2: Ka(acid)>Kb(base)
Ka(conjugate base)>Kb(conjugate acid)
acidic
vice versa=basic
How to know if amphiprotic ions are acidic or basic
see if Ka and Kb are higher
Relationship between Q and K
Q>K: shift left
Q
Effects of volume on equilibrium
Changing volume will change partial pressures, and therefore Q
Indirect relationship with pressure, directly effects pressure
Decrease volume: QK side with more moles
Effects of pressure on equilibrium
Increase pressure: decrease volume, go towards side with fewer moles
Decrease pressure; increase volume, go to side with more moles
What is used to prepare buffers?
- weak acids and their conjugate bases or weak bases and their conjugate acids
- weak acid and strong base
- weak base and strong acid
Equation for pH of a buffer solution
pH=pKa+log(Mf,base/Mf,acid)
or
pH=pKa+log(Mi,base•Vbase/Mi,acid•Vacid)
How to find final molarities of the acid and base components of buffers?
use M1V1=M2V2
Formulas for adding a strong base to a buffer solution
Mf,a,buff=(Mia,buff•Vbuff-Mbase•Vbase)/(Vbuf+Vbase)
Mf,b,buff=(Mib,buff•Vbuf+MbaseVbase)/(Vbuf+Vbase)
Formulas for adding a strong acid to a buffer solution
Mf,a,buff=(Mia,buf•Vbuf+Macid•Vacid)/(Vbuf+Vacid)
Mf,b,buf=(Mib,buf•Vbuf-Macid•Vacid)/(Vbuf+Vacid)
Strong acid-Strong base titration
Before equivalence point: Ma,f=(MaVa-MbVb)/(Vb+Va)
MaVa>MbVb
At equivalence point: MaVa=MbVb and pH=7
After equivalence point: MaVa
Strong base-strong acid titrations
Before equivalence point: Mb,f=MbVb>MaVa
Mb,f=(MbVb-MaVa)/(Vb+Va)
At equivalence point: MbVb=MaVa
pH=7
After equivalence point: MbVb
formula for change in temp(Arrhenius)
ln(k2/k1)=-Ea/R(1/T2-1/T1)
Titrating a weak acid with a strong base
Before equivalence point: MaVa>MbVb
Ma,f=(MaVa-MbVb)/(Vb+Va)
Mb, f= MbVb/(Vb+Va)
Henderson Hasselbalch can be used
At eq point: MaVa=MbVb(pH>7)
Msalt,f=MaVa/(Va+Vb)=MbVb/(Vb+Va)
equilibrium calculation with kb can be done
After eq point: MaVa
Titrating a weak base with a strong acid
Before eq point: MbVb>MaVa
Mb,f=(MbVb-MaVa)/(Vb+Va)
Ma,f=MaVa/(Vb+Va)
Henderson hasselbalch can be used
At eq point: MaVa=MbVb(pH<7)
Msalt,f=MaVa/(Vb+Va)=MbVb/(Vb+Va)
Salt hydrolysis: equilibrium calculation with Ka can be done
After eq point: MbVb
What happens to pure water as temperature increases?
Greater fraction of water molecules ionize as temp increases, and pH decreases
