Acids Bases Buffers

Question 1

Bronsted-Lowry Acid definition

Answer 1

Proton Donor

Question 2

Bronsted-Lowry Base definition

Answer 2

proton acceptor

Question 3

Kw

Answer 3

Kw = conc H+ x conc OH-

Question 4

value of Kw at 298 K

Answer 4

1.0 x 10-14

Question 5

what physical factors affect value of Kw

Answer 5

temperature only
if temperature is increased, the equilibrium moves to the right so Kw increases and the pH of pure water decreases

Question 6

why is pure water still neutral even if pH does not equal 7

Answer 6

conc. H+ = conc. OH-

Question 7

give an expression for pH in terms of H+

Answer 7

pH = -log10[H+]

Question 8

what is the relationship between pH and [H+]

Answer 8

lower pH = higher [H+]

Question 9

if two solutions have a pH difference of one what is the difference in [H+]

Answer 9

factor of 10

Question 10

how do you find [H+] from pH

Answer 10

[H+] = 10 to the power of -pH

Question 11

what is the difference when finding [H+] from concentration of diprotic and triprotic acids

Answer 11

need to multiply concentration of acid by number of protons to find [H+]

Question 12

how do you calculate the pH of a strong alkaline solution

Answer 12

use Kw to calculate [H+] from [OH-]
use pH=-log[H+]

Question 13

define strong acid

Answer 13

fully dissociates in water

Question 14

define strong base

Answer 14

fully dissociates in water

Question 15

what is the difference between concentrated and strong

Answer 15

concentrated means many mol per dm^3
strong refers to amount of dissociation

Question 16

what is a weak acid and weak base definition

Answer 16

do not fully dissociate in water
partially dissociate

Question 17

examples of strong acid

Answer 17

HCl, H2SO4, H3PO4

Question 18

examples of strong bases

Answer 18

NaOH, CaCO3, Na2CO3

Question 19

examples of weak acids

Answer 19

CH3COOH (any organic acids)

Question 20

example of weak bases

Answer 20

NH3

Question 21

what is Ka

Answer 21

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

Question 22

what is a titration

Answer 22

addition of an acid/base of known titration to base/acid of unknown titration to determine the concentration
indicator used to show neutralisation has occurred, as is a pH meter

Question 23

equivalence point definition

Answer 23

point at which exact volume of base has been added to just neutralise base

Question 24

what generally happens to pH of solution around equivalence point

Answer 24

there is a large and rapid change in pH, except in the weak-weak titration

Question 25

what is the end point

Answer 25

volume of acid or alkali added when the indicator just changes colour. if the right indicator is chosen, equivalence point= end point

Question 26

3 properties of a good indicator

Answer 26

sharp colour change (not gradual)

end point must be same as equivalence point

distinct colour change

Question 27

indicators for a strong acid - strong base titration

Answer 27

phenolphthalein or methyl orange

phenolphthalein has a clearer colour change though

Question 28

indicator for a strong acid - weak base titration

Answer 28

methyl orange

Question 29

indicator for a strong base-weak acid titration

Answer 29

phenolphthalein

Question 30

indicator for weak acid - weak base titration

Answer 30

neither methyl orange or phenolphthalein as neither give a sharp change at the end point

Question 31

methyl orange
- colour in acid
- colour in alkali
- at what pH does the colour change

Answer 31

red in acid
yellow in alkali
changes at p = 4-5 (approx same as pKa value)

Question 32

phenolphthalein
- colour in acid
- colour in alkali
- at what pH does the colour change

Answer 32

colourless in acid
red in alkali
changes about pH = 9-10 (approx same as pKa value)

Question 33

what is the half-neutralisation point

Answer 33

when volume = half the volume that has been added at the equivalence point

Question 34

define buffer solution

Answer 34

solution that can resist changes in pH when small amount of acid/alkali are added

Question 35

what do acidic buffer solutions contain in general terms

Answer 35

a weak acid and a soluble salt of the acid that fully dissociates

Question 36

write a reaction for an acidic buffer with added acid

Answer 36

A- + H+ –> HA
opposes addition of H+

Question 37

write a reaction for an acidic buffer with added alkali

Answer 37

HA + OH- –> H2O + A-

Question 38

how else can you achieve an acidic buffer solution other than just mixing the constituents

Answer 38

neutralise half of a weak acid (acid must be in excess) with an alkali forming a weak acid/soluble salt mixture

Question 39

what do basic buffer solutions contain in general terms

Answer 39

weak base and soluble salt of that weak base

Question 40

how can you calculate the pH of buffer solutions

Answer 40

use the Ka of the weak acid, sub in [A-] and [HA] to calculate [H+] then calculate pH

Question 41

how can you calculate the new pH of a buffer solution when acid or base is added

Answer 41

calculate number of moles of H+ and A- and HA before acid or base is added. use equations to work out new moles of A- and HA and find [H+] then pH

Question 42

which buffer system maintains blood pH at 7.4? what happens when acid/alkali is added?

Answer 42

H+ + HCO3 - <—-> CO2 + H2O

add OH- –> reacts with h+ to form H2O, then shifts equilibrium left to restore H+ lost

add H+ –> equilibrium shifts to the right, removing excess H+