Acid-base chemistry

Question 1

Buffers

Buffers definition

Answer 1

Composed of a weak acid/base and a conjugate salt. Example: NH4OH + NH4Cl

Question 2

Buffers

Buffer capacity

Answer 2

Defined as the amount of strong acid/base that must be added to 1L of the buffer solution to change pH by 1 unit.

Question 3

Buffers

Buffer effectiveness

Answer 3

Buffers are most effective when pka of the buffer is close to the pH of the solution

Question 4

Buffers

Henderson-Hasselbach equation

Answer 4

Question 5

Acid-base definitions

Arrhenius acid vs base

Answer 5

Arrhenius acid: produces H+.

Arrhenius base: produces OH-.

Question 6

Acid-base definitions

Brønsted-Lowry acid vs base

Answer 6

Brønsted-Lowry acid: donates H+ ion.

Brønsted-Lowry base: accepts H+ ion.

Question 7

Acid-base definitions

Lewis acid vs base

Answer 7

Lewis acid: accepts electron pair.

Lewis base: donates electron pair.

Question 8

Acid-base definitions

Amphoteric species

Answer 8

Can act as either acid or a base.

Question 9

Acid-base definitions

Polyprotic acid

Answer 9

Acid with multiple H+ ions.
Note that Ka1 > Ka2 > Ka3
Each ionization step becomes more difficult. As the compound becomes more negatively charged, it becomes harder to remove H+

Question 10

Titrations

Equivalence point

Answer 10

The point at which the equal amounts of acid and base have undergone the reaction. Also called endpoint.

Question 11

Titrations

Indicators

Answer 11

Weak acid/bases that change color when going from protonated to unprotonated form.

Important to choose an indicator whose pKa is close to the pH of the titration equivalence point so that it changes color in the appropriate range.

Note that indicators do not change the pH or buffering capacities of a solution, due to being added in miniscule amounts

Question 12

Titrations

Litmus paper

Answer 12

Indicator that turns red in presence of a Brønsted-Lowry acid (H+ donor) and blue in presence of a Brønsted-Lowry base (H+ acceptor)

Question 13

Titrations

Half-equivalence point

Answer 13

The point at which the concentration of acid equals the concentration of conjugate base. Also called the midpoint of the reaction.
[HA] = [A-]
pH = pKa

Question 14

Acid-base equilibrium

Strong vs weak

Answer 14

Strong acids/bases will completely dissociate whereas weak acids/bases will not.

Question 15

Acid-base equilibrium

Conjugate pairs

Answer 15

Strong acids have very weak conjugate bases and strong bases have very weak conjugate acids
Note that the inverse is not always true; weak acids do not always have strong conjugate bases and weak bases do not always have strong conjugate acids
The stability of the conjugate pair is a main factor in determining strength.

Question 16

Acid-base equilibrium

Acid dissociation constant

Answer 16

Question 17

Acid-base equilibrium

Base dissociation constant

Answer 17

Question 18

Acid-base equilibrium

pH vs pOH

Answer 18