Acids and Bases

Question 1

Arrhenius definition

Answer 1

An acid yields H3O+ and a base yields OH-

Question 2

Brondsted-Lowry definition

Answer 2

An acid is a proton (H+) donor and a base is a proton acceptor.

Question 3

Lewis acid definition

Answer 3

An acid is an electron-pair acceptor and a base is an electron-pair donor.

Question 4

What is pH?

Answer 4

pH = -log [H3O+]

Question 5

What is pOH?

Answer 5

pOH = -log [OH-]

Question 6

What are some equations for determining pH for weak reagents? (3)

Answer 6

Henderson-Hasselbalch equation
_______________________________________
pH = -log sqrt(Ka * [HA])

pH = (1/2) pKa - (1/2) log [HA]
note these two are close approximations only if the concentration is greater than the Ka and if pKa falls between 2 and 12.

Question 7

What is the -log(2*10^-3)? What relationship would be helpful to solve this?

Answer 7

3 - log 2

The relationship is: -log(z*10^-y) = y-log(z)

Question 8

Does the pH scale only range from 0 to 14?

Answer 8

NO.

Question 9

When an acid is mixed with water, it is said to ___________.

Answer 9

Dissociate

Question 10

When a base is mixed with water, it is said to __________.

Answer 10

undergo hydrolysis

Question 11

As acid strength increases, what happens to Ka, pka, conjugate base strength , kb, pKb?

Answer 11

Ka increases, pKa decreases, conjugate base strength decreases, Kb decreases, pKb increases.

Question 12

Name the strong acids and their pKa’s.

Answer 12

HCl (-7), HBr (-7), HI (-9), H2SO4 (-9 pKa1), HNO3 (-2), HClO4 (-10)

Question 13

What is a simple rule for determining acidity of oxyacids?

Answer 13

The more oxygen atoms there are bonded to the central atom, the more oxygen atoms withdraw electron density from the central atom, and thus the more acidic the oxyacid.

Question 14

When two compounds have the same excess oxygen count, the next factor to consider is what?

Answer 14

The electronegativity of the central atom.

Question 15

pH + pOH =

Answer 15

14

Question 16

What are the logs of 2 and 3? Use these to find the log of 4 and 5.

Answer 16

log 2 = 0.301 and log 3 = 0.477
log 4 = log (2*2) = log 2 + log 2 = 0.602
log 5 = log (10/2) = log 10 - log 2 = 1-0.301=.699

Question 17

Ka * Kb =

Answer 17

10^-14

Question 18

What equation is useful for buffer systems?

Answer 18

pH = pKa + log ([conjugate base]/[conjugate acid])

pH = pKa + log (moles conjugate base/ moles conjugate acid)

Question 19

Describe how the boiling point and freezing point are affected my acids.

Answer 19

Increasing the number of impurities dissolved into an aqueous solution raises the boiling point and lowers the freezing point of a solution. The total impurity concentration depends on the solute concentration, the number of particles id dissociates into, and the degree to which it dissociates.

Question 20

What is typical of the Ka values for weak acids?

Answer 20

Weak acids have Ka values that are less than one.

Question 21

A hydroxide anion is formed when water loses a proton (H+) to another water (known as autoionization). If the concentration of dissociated hydroxide anion (OH-) in distilled water is 1.0 x 10-6 M, the pH of the solution must be:
A . 7.0, because [H30+] = [OH-].
B. 7.0, because water always has a pH of 7.0.
C. 6.0, because [H30+] = [OH-].
D. 8.0, because the solution is rich in base (OH”).

Answer 21

Choice C is correct. The first word in the question is “If”, so keep that in mind. The mantra that you chant about water having a pH of 7 does not apply in this speculative question. If the only hydroxide ion in solution is formed when one molecule of water loses a proton to another molecule of water, then the hydroxide anion concentration [OH-] must equal the hydronium cation concentration ([H3O+]).

Question 22

All of the following qualifications affect the acidity of an oxyacid EXCEPT:
A . the oxidation state of the central atom.
B. the electronegativity of the central atom.
C . the size of the central atom.
D . the number of π-bonds to the central atom.

Answer 22

Choice C is correct. As the oxidation state of the central atom in an oxyacid increases, the compound becomes more acidic. This is because the number of π-bonds between oxygen atoms and the central atom increases. This increase in π-bonds results in more electron withdrawal (by way of resonance) from the central atom, making it electron-poor. The compound therefore becomes more acidic. This means that both the oxidation state and the number of π-bonds to the central atom affect the acidity of the oxyacid, so choices A and D are eliminated. As the electronegativity of the central atom in an oxyacid increases, the compound becomes more acidic. This is because of the inductive effect. The increase in electron withdrawal from the central atom, due to the inductive effect, makes the central atom electron-poor. This means that the electronegativity of the central atom affects the acidity of the oxyacid, so choice B is eliminated. The size of the central atom has no bearing on the acidity of the oxyacid, because the acidic proton is not directly bonded to the central atom. Tins makes choice C the
best answer.

Question 23

An increase in pH means?

Answer 23

LESS acidic

Question 24

For a triprotic acid, how do the pKa’s and pKb’s relate?

Answer 24

pKa1 + pKb3 = 14
pKa2 + pKb2 = 14
pKa3 + pKb1 = 14