acids, bases, buffers

Question 1

write an expression for how to calculate pH

Answer 1

pH = - log [H+]

Question 2

explain how to calculate the pH of a strong acid

Answer 2

concentration of acid = [H+] because it is fully dissociated in water

Question 3

what are the assumptions made in the calculation of a strong acid

Answer 3

the acid is full dissociated

[acid] = [H+]

Question 4

explain how to calculate [H+] from a given pH

Answer 4

[H+] = 10 to power of -pH

Question 5

define bronsted lowry acid

Answer 5

proton donor

Question 6

define bronsted lowry base

Answer 6

proton acceptor

Question 7

explain the difference between a weak and strong acid

Answer 7

strong acids are fully dissociated in water, weak acids only partially dissociate in water

Question 8

write the equation for the reaction of a strong acid with water

Answer 8

HA + H2O –> H3O+ + A-

Question 9

write an equation for the reaction of a weak acid with water

Answer 9

HA + H20 ⇌ H3O+ + A-

Question 10

explain how to calculate [H+] for H2SO4

Answer 10

2 x concentration of acid = [H+] because its diprotic

Question 11

write an expression for the ionic product of water (Kw)

Answer 11

Kw = [H+] [OH-]

Question 12

modify Kw to calculate the pH of pure water

Answer 12

Kw = [H+] squared

Question 13

what assumption is made in the calculation of pH of pure water

Answer 13

that each water molecule dissociates to give H+ and OH-

Question 14

explain how to calculate pH of a strong base

Answer 14

assume concentration of base is equal to [OH-] concentration , then use the Kw expression

Question 15

explain how to calculate [OH-] of barium hydroxide

Answer 15

Ba(OH)2 therefore 2x the concentration of BaOH2 = [OH-]

Question 16

explain why pure water is always neutral regardless of the pH

Answer 16

[H+] = [OH-] at any temperature

for an acid [H+] > [OH-]
for a base [H+] < [OH-]

Question 17

calculate pKa

Answer 17

pKa = - log Ka

Question 18

calculate Ka from pKa

Answer 18

Ka = 10 to power of -pKa

Question 19

write an expression for Ka

Answer 19

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

Question 20

define a buffer solution

Answer 20

a solution that resists the change in pH when a small amount of acid or alkali are added

Question 21

write a modified expression for Ka when doing buffer calculation

Answer 21

Ka = [H+] x (salt/acid)

Question 22

how do you make a buffer

Answer 22

mixture of a weak acid and it’s sodium salt

Question 23

what happens to the reaction of

HA reversible reaction arrow when NaOH is added when a buffer is present

Answer 23

H+ + OH- —> H2O

concentration of H+ ions decreases therefore equilibrium shifts to right

no change in pH

Question 24

write an equation for the disassociation of a weak acid HA

Answer 24

HA ⇌ H+ + A-

Question 24

what happens if HCl is added to this reaction:

HA ⇌ H+ + A-

Answer 24

H+ concentration increases

equilibrium shifts to left to oppose the change

A- is needed to react with H+ but conc is very small is runs out quickly

Question 25

what happens when NaOH is added to weak acid HA that has a buffer

Answer 25

buffers equilibrium by shifting it right

Question 26

what happens if HCl is added to weak acid HA

Answer 26

cannot buffer
not enough A- for equilibrium to shift left