acids and bases

Question 1

what is a brønsted-lowry acid?

Answer 1

a proton donor

Question 2

what is a brønsted-lowry base?

Answer 2

a proton acceptor

Question 3

what does ‘strong’ mean in terms of acids and bases?

Answer 3

completely dissociates in solution

Question 4

what are some examples of strong acids?

Answer 4

HCl, H2SO4 + HNO3

Question 5

what does monoprotic mean?

Answer 5

1mol of acid produces 1mol of H+

Question 6

what does diprotic mean?

Answer 6

1mol of acid produces 2mol of H+

Question 7

what are strong bases?

Answer 7

they produce OH- if the base dissolves in water

Question 8

what are some examples of strong bases?

Answer 8

KOH, NaOH, CuOH

Question 9

what is meant by ‘weak’ in terms of acids and bases?

Answer 9

only slightly dissociate in solution

Question 10

constituent elements: weak acids are mainly…

Answer 10

“carbon containing” (organic)
e.g., ethanoic acid

Question 11

what is an example of a weak base?

Answer 11

ammonia

Question 12

where does the position of equilibrium lie for weak acids and bases?

Answer 12

far to the left

Question 13

what scale is used to measure pH?

Answer 13

the pH scale (logarithmic)
a difference of 1 on the pH scale is a 10x increase/decrease of [H+]

Question 14

what formula do we use to calculate pH?

Answer 14

pH = –log10[H+]

Question 15

what formula do we use to calculate [H+] using pH?

Answer 15

[H+] = 10(-pH)

Question 16

what is the pH of neutral solutions?

Answer 16

pH 7 at room temp.

Question 17

what is an alkali?

Answer 17

a soluble base

alkaline solutions = when bases dissociate in water

Question 18

what is Ka?

Answer 18

the acid dissociation constant - this is only applicable for WEAK ACIDS, due to them only partially dissociating

Question 19

what is the relationship between Ka and acid dissociation?

Answer 19

the higher the value for Ka, the more the acid will dissociate when placed in solution; strong acids have exceptionally high Ka values

Question 20

what equilibrium do we need to consider when looking at Ka?

Answer 20

HA ⇌ H+ + A-

Question 21

what is the formula for Ka?

Answer 21

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

Question 22

what are the units used for Ka?

Answer 22

mol dm-3

Question 23

how would the formula look for a PURE SOLUTION of a weak acid?

Answer 23

Ka = [H+]^2/[HA]

Question 24

what is the formula for calculating pKa?

Answer 24

pKa = -log(Ka)

Question 25

what is the formula for calculating Ka from pKa?

Answer 25

Ka = 10^(-pKa)

Question 26

what assumption do we make about HA?

Answer 26

that the [HA] at equilibrium is the same as the [HA] initially - we assume this as we say that the acid is so weak, barely any of it has dissociated. Again, this is only applicable for pure solutions of the weak acid.

Question 27

what does Kw denote?

Answer 27

the ionic product of water

Question 28

what equilibrium are we considering when looking at Kw?

Answer 28

H2O ⇌ H+ + OH-

Question 29

what is the formula for calculating Kw?

Answer 29

Kw = [H+][OH-]

Question 30

what are the units for Kw?

Answer 30

mol2 dm-6

Question 31

what is the value of Kw AT ROOM TEMP?

Answer 31

1.00 x10^-14 ; if the value is not given within the question, we assume this value

Question 32

why does pure water remain pure, despite a pH different to 7?

Answer 32

for water to be pure, [H+] has to be equal to [OH-]

Question 33

how would the formula look different for Kw of PURE water?

Answer 33

Kw = [H+]^2

Question 34

how many types of different titration curves are there?

Answer 34

four: weak acid-weak base weak acid-strong base strong acid-weak base strong acid-strong base

Question 35

what is the definition of equivalence point?

Answer 35

the point at which the moles of acid and the moles of base present would neutralise each other

Question 36

what is the definition of end-point?

Answer 36

the point at which the indicator changes colour

Question 37

what pH does the inflection occur for strong acid-strong base?

Answer 37

between pH2 and pH11

Question 38

what pH does the inflection occur for strong acid-weak base?

Answer 38

between pH2 and pH8

Question 39

what pH does the inflection occur for weak acid-strong base?

Answer 39

between pH6 and pH11

Question 40

what pH does the inflection occur for weak acid-weak base?

Answer 40

there is no major point of inflection

Question 41

what is the choice of indicator dependent on?

Answer 41

the pH in which the indicator changes colour must work with the pH at which the equivalence point is - it must be within the inflection pH of the curve

Question 42

what are the two main indicators for titrations?

Answer 42

phenolphthalein and methyl orange

Question 43

what is the colour change for phenolphthalein?

Answer 43

colourless in acid --> pink in base

Question 44

what is the pH range of the colour change for phenolphthalein?

Answer 44

pH8.3 - pH10. appropriate for titrations including a strong base

Question 45

what is the colour change of methyl orange?

Answer 45

red in acid --> yellow in base

Question 46

what is the pH range of the colour change for methyl orange?

Answer 46

pH3.1 - pH4.4

Question 47

what does dilution involve?

Answer 47

changes in the conc. of H+/OH- in the solution - this is therefore accompanied by a change in the pH of the solution

Question 48

what is the formula for calculating the new conc. of a solution following dilution?

Answer 48

new conc. of solution = moles of solute/new total volume.

Question 49

what is the definition of a buffer?

Answer 49

buffers are solutions which can resist small changes in pH caused by dilution/addition of small amt. of acid/base.

Question 50

what are the two main types of buffer?

Answer 50

acidic buffers and basic buffers

Question 51

buffer action: what happens when a small amt of dilute acid is added?

Answer 51

- addition of extra acid involves addition of extra H+ - A- (acid) reacts with the H+ and removes them from the solution - this keeps the pH almost constant

Question 52

buffer action: what happens when a small amt of dilute base is added?

Answer 52

- addition of extra base involves addition of extra OH- - OH- reacts with the H+ (small amt), removing some H+ from solution - however, position of equilibrium shifts right to restore the H+, which keeps the pH almost constant

Question 53

what does an acidic buffer consist of?

Answer 53

an excess of weak acid and its salt e.g. CH3COONA and CH3COOH can be mixed to form a buffer. alternatively, the CH3COONA may be formed indirectly from the reaction of NaOH with excess CH3COOH

Question 54

what does a basic buffer consist of?

Answer 54

an excess of weak base and its salt

Question 55

what formula do we consider when finding the pH of a buffer solution?

Answer 55

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