unit 1b: pH

Question 1

water dissociation

Answer 1

in water and aqueous solution, there is an equilibrium between the water molecules and hydronium and hydroxide ions

Question 2

hydronium ion

Answer 2

H3O^+ (H^+ (aq) shorthand)

Question 3

brønsted-lowry definition of acids and bases

Answer 3

an acid is a proton donor, a base is a proton acceptor

Question 4

when an acid donates a proton, the species left behind is the

Answer 4

conjugate base of the acid

Question 5

when a base accepts a proton, the species formed is called the

Answer 5

conjugate acid of the base

Question 6

amphoteric

Answer 6

it can react as both an acid and a base (water is amphoteric)

Question 7

the dissociation constant

Answer 7

Kw, known as the ionic product of water

Question 8

ionic product of water

Answer 8

[H3O^+] [OH^-]

Question 9

Kw varies with

Answer 9

temperature

Question 10

at 25°C, the value of Kw is

Answer 10

approximately 1x10^-14

Question 11

in water and aqueous solutions with a pH value of 7, the concentrations of hydronium and hydroxide ions are

Answer 11

10^-7 moll^-1 at 25°C

Question 12

strong acids and bases

Answer 12

those that completely dissociate (ionise) when dissolved in water

Question 13

examples of strong acids

Answer 13

sulphuric acid, nitric acid, hydrochloric acid

Question 14

examples of strong bases

Answer 14

sodium hydroxide, potassium hydroxide

Question 15

weak acids and bases

Answer 15

only partially dissociate in water, an equilibrium (which lies to the left) is set up

Question 16

examples of weak acids

Answer 16

carboxylic acids

Question 17

examples of weak bases

Answer 17

ammonia, amines

Question 18

equimolar solutions

Answer 18

same concentration

Question 19

compared to a weak acid, a strong acid has

Answer 19

lower pH, higher conductivity, faster rate of reaction

Question 20

compared to a weak base, a strong base has

Answer 20

higher pH, higher conductivity, faster rate of reaction

Question 21

acid dissociation constant

Answer 21

Ka

Question 22

pKa values are used when

Answer 22

calculating the pH of a weak acid to take into account the degree of dissociation

Question 23

the larger the pKa

Answer 23

the weaker the acid

Question 24

a salt of a strong acid and a weak base will form

Answer 24

an acidic solution

Question 25

a salt of a weak acid and a strong base will form

Answer 25

a basic solution

Question 26

a salt of a strong acid and a strong base will form

Answer 26

a neutral solution

Question 27

when in solution, all salts…

Answer 27

completely ionise

Question 28

a buffer solution

Answer 28

one in which the pH remains approximately constant when small amounts of acid, base, or water are added

Question 29

use of buffers

Answer 29

stabilise pH by being able to absorb extra acid or alkali

Question 30

acid buffer

Answer 30

a solution of a weak acid and a salt of the weak acid

Question 31

basic buffer

Answer 31

a solution of a weak base and a salt of the weak base

Question 32

acid buffer solution use

Answer 32

when a base is added it removes H+ ions, the weak acid can supply hydrogen ions. when an acid is added it adds H+ ions, the salt provides the conjugate base which removes extra H+ ions

Question 33

basic buffer solution use

Answer 33

when an acid is added it adds H+ ions, the weak base removes hydrogen ions. when a base is added it removed H+ ions, the salt provides the conjugate acid which supplies H+ ions

Question 34

adding water to a buffer

Answer 34

does not affect the pH as [acid]/[salt] is a ratio

Question 35

indicators

Answer 35

are weak acids which change colour depending on pH

Question 36

acid indicator dissociation constant

Answer 36

KIn

Question 37

the colour of an acid indicator

Answer 37

is distinctly different to the colour of its conjugate base

Question 38

colour change in an indicator can only be distinguished when

Answer 38

HIn and In- differ by a factor of 10

Question 39

acid indicator shorthand

Answer 39

HIn

Question 40

conjugate base indicator shorthand

Answer 40

In-

Question 41

equivalence point for strong acid/ strong base

Answer 41

pH7, an indicator which changes colour around pH7 is suitable

Question 42

equivalence point for a strong acid/ weak base

Answer 42

around pH5, an indicator which changes colour at an acid pH is suitabel

Question 43

equivalence point for a weak acid/ strong base

Answer 43

around pH9, an indicator which changes colour at a basic pH is suitable

Question 44

suitable indicator for weak acid/ weak base

Answer 44

not possible as the pH does not change rapidly enough, the curve does not have a vertical section like the others

Question 45

equivalence point

Answer 45

the mid point of the rapid increase in pH

Question 46

concentration=

Answer 46

10^-pH

Question 47

why does adding H+ to the salt of the weak acid result in the formation of undissociated weak acid molecules

Answer 47

H+ ions react with the conjugate base