T12 Acid-base equilibria

Question 1

acids

Answer 1

proton donors, releasing H + ions in water to form hydroxonium ions (H3O+)

Question 2

bases

Answer 2

proton acceptors

take H+ ions from water molecules in solution to form OH- ions

Question 3

strong acids /bases

Answer 3

dissociate completely in water

e.g HCl/ NaOH

Question 4

weak acids/bases

Answer 4

dissociate partially in water

forms an equilibrium lying to the left

Question 5

conjugate pairs

Answer 5

species linked by the transfer of a proton

Question 6

conjugate base

Answer 6

species that has lost a proton

Question 7

conjugate acid

Answer 7

species that has gained a proton

Question 8

neutralisation reactions

Answer 8

when acids and base react together to form water and a salt.

Question 9

neutral solution

Answer 9

equal conc of H+ and OH- ions

Question 10

standard enthalpy change of neutralisation

Answer 10

enthalpy change when solutions of an acid and base react under standard conditions to produce one mole of water.
always negative as is exothermic

Question 11

weak acid base neutralisation enthalpy

Answer 11

vary as only dissociate partially/reversibly and ions get used up quickly

Question 12

strong acid base neutralisation enthalpy

Answer 12

no dissociation enthalpy just the reaction of H+ and OH- ions

Question 13

pH equation

Answer 13

-log10(H+)

Question 14

pH define

Answer 14

measure of hydrogen ion concentration

Question 15

monoprotic acids

Answer 15

each mole of acid produces one mole of hydrogen ions

Question 16

acid conc for strong, monoprotic acids

Answer 16

concentration of H+ ions

Question 17

how do you find H+ conc from the pH

Answer 17

10 to the negative pH

Question 18

polyprotic acids

Answer 18

acids with more than one proton available to release into solution.

Question 19

how do you find pH of a weak acid

Answer 19

Ka

Question 20

Ka

Answer 20

acid dissociation constant

Question 21

Ka equation

Answer 21

(H+ conc * acid conc at eq)/conc of acid at start

Question 22

Kc

Answer 22

equilibrium constant

Question 23

Kw

Answer 23

ionic product of water

Question 24

Kw equation

Answer 24

concentration of OH- * concentration of H+

Question 25

what’s Kw units

Answer 25

mol^2dm^-6

Question 26

Kw of pure water

Answer 26

conc of H+ squared

Question 27

Kw at 25 degrees celsius or 298 K

Answer 27

1*10^-14

Question 28

pKw

Answer 28

-log10(Kw)

Question 29

Kw from pKw

Answer 29

10^-pKw

Question 30

pKa

Answer 30

-log10(Ka)

Question 31

how to calibrate a pH meter

Answer 31

place in deionised water and set to 7 and repeat w standard pH solutions, washing with deionised water after every one.

Question 32

effects of diluting by a factor of 10 in strong acids

Answer 32

increases pH by 1

Question 33

effects of diluting by a factor of 10 in weak acids

Answer 33

increases pH of 0.5

Question 34

basics of how to titrate

Answer 34

measure out base with a pipette and put in a flask with an indicator.
rinse burette w acid standard solution before filling
carry out rough titration and note end point
repeat to receive concordant results (within 0.1 cm cubed of each other)

Question 35

equivalence line

Answer 35

almost vertical line on a titration curve upon which the end point lies in which all the acid has been neutralised

Question 36

methyl orange
color at low/high pH
pH of colour change

Answer 36

red at low, yellow at high

3.1-4.4

Question 37

phenolpthalein
color at low/high pH
pH of colour change

Answer 37

colourless at low
pink at high
8.3-10

Question 38

half-equivalence

Answer 38

the stage of the titration when all of the acid has been neutralised
pH at half-equivalence is actually the pKa for the acid

Question 39

buffer

Answer 39

solution that minimises change in pH when small amounts of acid or base are added.

Question 40

acidic buffer composition

Answer 40

a weak acid and a conjugate base

Question 41

how do you make acidic buffers

Answer 41

mix an excess of weak acid with a strong base

mix a weak acid with the salt of its conjugate base

Question 42

what happens when you mix excess weak acid with a strong base

Answer 42

all of the base reacts w the acid

leftover weak acid slightly dissociates

Question 43

what happens when you mix a weak acid with the salt of its conjugate base

Answer 43

salt will fully dissociate into its ions when it dissolves

ethanoic acid partially dissociates