Princeton Ch 11 - Acids and Bases

Question 1

Bronsted Lowry Acid and Bases.

Answer 1

Acids are proton (H+) donors; bases are proton (H+) acceptors.

Question 2

Lewis Acids and Bases.

Answer 2

Lewis acids are electron pair acceptors. Lewis bases are electron pair donors.

Question 3

Difference between a strong and weak acid.

Answer 3

A strong acid is one that dissociates completely in water. Weak acids do not go to completion.

Question 4

The strength of an acid is directly related to how much the products are favored over the reactants. What’s the equilibrium expression for the reaction of an acid with water?

Answer 4

Ka = [H3O+][A-]/[HA]

Question 5

The larger the Ka value, the (stronger/weaker) the acid. The smaller the Ka value, the (stronger/weaker) the acid.

Answer 5

The larger the Ka value, the stronger the acid. The smaller the Ka value, the weaker the acid.

The smaller the pkA, the stronger the acid.

Question 6

There are about 6 strong acids you should have memorized. What are they?

Answer 6

HI, HBr, HCl
HClO4; perchloric acid
H2SO4; sulfuric acid
HNO3; nitric acid

*** Assume any acid not listed above as weak (unless told)

Question 7

Base dissociation constant.

Answer 7

Kb = [Hb][OH-]/[B]

Question 8

There are 4 types of common strong bases. What are they?

Answer 8

Group 1 hydroxides: (NaOH)
Group 1 oxides: Li2O
Some group 2 hydroxides: Ba(OH)2; Sr(OH)2; Ca(OH2)
Metal amides: NaNH2

Question 9

The conjugate base of a strong acid has (strong/weak/no) basic properties.
The conjugate base of a weak acid has (strong/weak/no) basic properties.

Answer 9

The conjugate base of a strong acid has NO basic properties in water.

The conjugate base of a weak acid is a WEAK base.

Question 10

The conjugate acid of a strong base has (strong/weak/no) basic properties.

The conjugate base of a weak base has (strong/weak/no) acidic properties.

Answer 10

The conjugate acid of a strong base has NO basic properties in water.

The conjugate base of a weak base is a weak acid. Th weaker the base, the stronger the acid.

Question 11

Amphoteric compound.

Answer 11

Whenever a substance can act as either an acid or base, we say that it is amphoteric. The conjugate base of a weak polyprotic acid is always amphoteric because it can either accept or donate a H+.

Question 12

Equilibrium expression for the autoionization of water.

Answer 12

Kw = 1.0 *10^-14

Kw is constant at a given temperature and like all other equilibrium constants increases with temperature.

Question 13

If the introduction of an acid increases the concentration of H3O+ ions, then the eq is disturbed and the reverse reaction is favored, decreasing the concentration of OH- ions. What happens to the Kw in this case?

Answer 13

The [ ] product of H3O+ and OH- will remain equal to Kw.

Question 14

Give two definitions of PH.

Answer 14

pH = -log[H+]

measures the concentration of H+ ions in a solution.

Question 15

pH + pOH = ?

Answer 15

pH + pOH = 14

Question 16

pOH = ?

Answer 16

pOH = -log[OH-]

Question 17

pKa =? pKb = ?

Answer 17

pKa = -logKa 
pKb = -log Kb

Question 18

Ka *Kb = ? (for an acid base conjugate pair)

Answer 18

Ka Kb = Kw = 1 10 ^-14 ( at 25C)

Question 19

pKa + pKb = ?

Answer 19

pKa + pKb = 14

Question 20

How can you calculate the pH if a strong acid is added to a solution of water?

Answer 20

Strong acids dissociate completely, so the [H+] will be the same as the concentration of the acid. You can calculate the pH directly from the molarity of the solution. Ex. 0.01M solution of HCl will have [H+] = 0.0M and pH = 2.

Question 21

Weak acids come to equilibrium with their dissociated ions. For a weak acid at eq. the concentration of undissociated acid will be much greater than the concentration of H+ ion. To find the pH you need a eq expression.

Answer 21

Ex. HCN at 0.2 molar

Ka = [H+][CN-]/HCN = x²/ (0.2 -x); x = moles of HCN that are dissociated. Since it’s a weak acid, the x added or substrated is negligible. If K <10^-4, you can assume x = 0.

Question 22

Buffer solution

Answer 22

A solution that resists changes in pH when a small amount of acid or base is added.

Question 23

Henderson Hasselback equation for acid and base.

This equation is helpful in buffer or indicator design.

Answer 23

pH = pka + log ([A-/HA]) –> pka + log (conj. base/weakacid)

pOH = pkb + log(conj. acid/weak base)

Question 24

Indicator.

Answer 24

An indicator is a waek acid that undergoes a color change when it’s converted to its conjugate base.

HA + H2O H3O+ + A-

[H3O+]/Ka = [HA]/[A]

Question 25

If [H3O+]&raquo_space; Ka. then [HA]&raquo_space;[A-] so we’d see what color for an idicator?
If [H3O+] = Ka. then [HA] = [A-] so, we’d see:
If [H3O+] <

Answer 25

If [H3O+]&raquo_space; Ka. then [HA]&raquo_space;[A-]; we’d see color 1 (HA)
If [H3O+] = Ka. then [HA] = [A-] so, we’d see mix
If [H3O+] <

Question 26

Phenolphthalein is an indicator with a pka of 9.0. When added to a solution whose pH is less than 8, the color ____.

Answer 26

Remains the same/colorless. Typically, indicator color changes within 2 units of the pH range. If the solution is above 10, it will turn purple. If 8

Question 27

Acid-base titration.

Answer 27

An acid-base titration is an experimental technique used to determine the identity of an unknown weak acid or weak base. The procedure entails adding a strong acid or base of a known identity and concentration (the titrant) to a solution containing the unknown base (or acid).

Question 28

Equivalence point of titration.

Answer 28

When just enough base has been added to neutralize alll the acid.