Chapter 20: Acids, Bases, and pH (20.1-20.5)

Question 1

what is a bronsted-lowry acid?

Answer 1

a H+/proton donor

Question 2

what is a bronsted-lowry base?

Answer 2

a H+/proton acceptor

Question 3

the general equation for acid dissociation

Answer 3

HA < – > H+ + A-

A- is the conjugate base

Question 4

Define a conjugate acid-base pair

Answer 4

a conjugate acid-base pair contains 2 species that can be interconverted by transfer of a proton
(eg HNO3 and NO3- can be interconverted by transfer of a proton/H+ ion)

Question 5

define monobasic acid

Answer 5

has 1 proton (H+) that can be replaced in an acid-base reaction

Question 6

define dibasic acid

Answer 6

has 2 protons (H+) that can be replaced in an acid-base reaction

Question 7

define tribasic acid

Answer 7

has 3 protons (H+) that can be replaced in an acid-base reaction

Question 8

hydronium ion

Answer 8

H3O+

Question 9

what is a salt

Answer 9

a salt is the product of a neutralisation reaction with an acid and a base where the H+ ion has been replaced with either a metal or ammonium (NH4+)

Question 10

a strong acid

Answer 10

releases all of its H+ ions in aqueous solution
HA –> H+ + A-
example: HCl, H2SO4

Question 11

weak acid

Answer 11

does not release all of its H+ ions in aqueous solution
HA < – > H+ + A-
example: all organic acids eg CH3COOH

Question 12

equation for pH

Answer 12

pH = -log[H+]

use base 10

Question 13

acid dissociation constant or Ka

Answer 13

Ka = [H+][A-] / [HA]
or  = [H+]^2 / [HA]

HA < – > H+ + A- (Ka is only for weak acids)

Question 14

pKa =

Answer 14

-log(Ka)

base 10

Question 15

dilute acid + metal –>

redox

Answer 15

salt + H2

eg 2H+(aq) + Zn(s) –> Zn 2+(aq) + H2(g)

Question 16

common bases

Answer 16

carbonates, metal oxides, metal hydroxides, alkalis

Question 17

acid + carbonate –>

neutralisation

Answer 17

salt + water + CO2

eg 2H+(aq) + CaCO3(s) –> Ca 2+(aq) + H2O(l) + CO2(g)

Question 18

acid + metal oxide (s) –>
acid + metal hydroxide (s) –>
(neutralisation, they are the same)

Answer 18

salt + water

Question 19

acid + alkali –>

neutralisation

Answer 19

H2O

eg H+(aq) + OH-(aq) –> H2O (l)

Question 20

[H+] =

Answer 20

[H+] = 10^(-pH)

Question 21

larger acid dissociation (Ka) means

Answer 21

stronger acid

Question 22

a larger pKa means

Answer 22

a weaker acid (a smaller Ka)

Question 23

neutralisation is

Answer 23

a chemical reaction in which an acid and a base reacts to form water

Question 24

in strong acids: [H+] =

Answer 24

[H+] = [HA]

Question 25

weak acid:
[HA] (at equilibrium) =

And why does this not necessarily work for ‘stronger’ weak acids?

Answer 25

[HA(aq)] (start)&raquo_space; [H+(aq)] (equilibrium)
HA(aq) = [HA(aq)] (start) - [H+(aq)] (eqm)
[HA] (at eqm) ~ [HA] (at start)

Breaks down when [H+] becomes significant and there is a real difference between
[HA(aq)] (equilibrium) and [HA(aq)] (start) - [H+(aq)] (equilibrium)

Question 26

what is Kw (definition)

Answer 26

the ionic product of water
H2O dissosiates slightly, acting as a weak acid
H2O < – > H+ + OH-

Question 27

what is Kw (equation)

Answer 27

Kw = [H+] X [OH-]

you are given the value of Kw

Question 28

what is Kw (number value)

Answer 28

Kw (at rtp) = 1 X 10^-14

Question 29

if [H+] = [OH-]

Answer 29

solution is neutral

Question 30

if [H+] > [OH-]

Answer 30

solution is acidic

Question 31

if [H+] < [OH-]

Answer 31

solution is alkali

Question 32

strong bases

Answer 32

completely dissociate in aqueous solution

KOH –> K+ + OH-

Question 33

how to find the pH of a strong base

Answer 33

[KOH] = [OH-]
then use Kw = [H+][OH-] to find [H+]
use pH = -log[H+]

Question 34

Why do we use pH rather than [H+]?

Answer 34

pH makes the numbers more manageable, as it takes a log of the really small [H+] values

Question 35

Weak acid approximation for [H+] at equilibrium

Answer 35

[H+] (equilibrium) ~ [A-] (equilibrium]

i.e there is a negligible dissociation of water (weak solutions would cause there to be more H+ due to its dissociation in water)