Exam 2

Question 1

conjugate base

Answer 1

species that remains when a proton has been removed from an acid

Question 2

Conjugate acid

Answer 2

species that forms when attaches to a base

Question 3

Arrhenius and bronsted lowry acid/base definitions

Answer 3

Arrhenius: Acids yield H+ and bases yield OH-

Bronsted-lowry: acids donate H+ and bases accept H+

Question 4

Relationship between Kw and temp

Answer 4

direct

Question 5

Formula for how many times faster a reaction is with a catalyst or for change in Ea

Answer 5

ln(k1/k2)=(Ea1-Ea2)/RT

Question 6

How is pH of polyprotic acids determined?

Answer 6

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

Question 7

degree of ionization

Answer 7

d=|H+| / |HA|i

Question 8

Factors affecting acid strength

Answer 8

1. 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
2. Higher oxidation number of central atom=stronger acid
3. Higher electronegativity of halogen atom=stronger

Question 9

Exception to acid strength trends

Answer 9

H3PO4 is not stronger than H3PO3 because H3PO3 is diprotic

Question 10

how do qualitatively determine pH of salts of weak acids and bases

Answer 10

1. pKa=pKa: neutral

2: Ka(acid)>Kb(base)
Ka(conjugate base)>Kb(conjugate acid)
acidic

vice versa=basic

Question 11

How to know if amphiprotic ions are acidic or basic

Answer 11

see if Ka and Kb are higher

Question 12

Relationship between Q and K

Answer 12

Q>K: shift left

Q

Question 13

Effects of volume on equilibrium

Answer 13

Changing volume will change partial pressures, and therefore Q

Indirect relationship with pressure, directly effects pressure

Decrease volume: QK side with more moles

Question 14

Effects of pressure on equilibrium

Answer 14

Increase pressure: decrease volume, go towards side with fewer moles

Decrease pressure; increase volume, go to side with more moles

Question 15

What is used to prepare buffers?

Answer 15

1. weak acids and their conjugate bases or weak bases and their conjugate acids
2. weak acid and strong base
3. weak base and strong acid

Question 16

Equation for pH of a buffer solution

Answer 16

pH=pKa+log(Mf,base/Mf,acid)

or

pH=pKa+log(Mi,base•Vbase/Mi,acid•Vacid)

Question 17

How to find final molarities of the acid and base components of buffers?

Answer 17

use M1V1=M2V2

Question 18

Formulas for adding a strong base to a buffer solution

Answer 18

Mf,a,buff=(Mia,buff•Vbuff-Mbase•Vbase)/(Vbuf+Vbase)

Mf,b,buff=(Mib,buff•Vbuf+MbaseVbase)/(Vbuf+Vbase)

Question 19

Formulas for adding a strong acid to a buffer solution

Answer 19

Mf,a,buff=(Mia,buf•Vbuf+Macid•Vacid)/(Vbuf+Vacid)

Mf,b,buf=(Mib,buf•Vbuf-Macid•Vacid)/(Vbuf+Vacid)

Question 20

Strong acid-Strong base titration

Answer 20

Before equivalence point: Ma,f=(MaVa-MbVb)/(Vb+Va)
MaVa>MbVb

At equivalence point: MaVa=MbVb and pH=7

After equivalence point: MaVa

Question 21

Strong base-strong acid titrations

Answer 21

Before equivalence point: Mb,f=MbVb>MaVa
Mb,f=(MbVb-MaVa)/(Vb+Va)

At equivalence point: MbVb=MaVa
pH=7

After equivalence point: MbVb

Question 22

formula for change in temp(Arrhenius)

Answer 22

ln(k2/k1)=-Ea/R(1/T2-1/T1)

Question 23

Titrating a weak acid with a strong base

Answer 23

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

Question 24

Titrating a weak base with a strong acid

Answer 24

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

Question 25

What happens to pure water as temperature increases?

Answer 25

Greater fraction of water molecules ionize as temp increases, and pH decreases