5.1.3 Acids, bases, and buffers Flashcards

1
Q

Brønsted-Lowry acid

A

species that donates a proton

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Brønsted-Lowry base

A

species that accepts a proton

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

conjugate acid-base pair

A

can be interconverted by the transfer of a proton

eg. HCl and Cl-

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

what does monobasic, dibasic and tribasic refer to

A

the no. hydrogen ions that can be replaced per molecule in an acid-base reaction eg. by metal/ammonium ions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

mathematical relationship between pH and [H+] (two equations)

A
pH = -log[H+]
[H+] = 10^-pH
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

assumptions when calculating the pH of strong acids

A

acid completely dissociates, therefore [HA] = [H+] and you can calculate the pH directly from the conc of the acid

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

what’s the difference in [H+] between pH 2 and pH 1?

A

the [H+] is 10x greater at pH 1 than at pH 2

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

mathematical relationship between pKa and Ka (two equations)

A
pKa = -log(Ka)
Ka = 10^-pKa
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is Ka

A

the acid dissociation constant

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

what are the Ka and pKa values of a strong acid

A

high Ka

low pKa

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

assumptions when calculating the pH of weak acids

A
  1. negligible dissociation of H₂O
    - -> [H+]equilibrium = [A-]equilibrium
  2. no dissociation of HA
    - -> [HA]equilibrium = [HA]start
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

limitations of the two assumptions used when calculating the pH of weak acids

A
  1. negligible dissociation of H₂O
    - breaks down with very weak acids as dissociation of water becomes significant in comparison to dissociation of acid
  2. no dissociation of HA
    - breaks down for stronger weak acids as dissociation of HA becomes significant
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Kw (what is it, equation, value at 298K)

A

ionic product of water
Kw = [H+][OH-]
1.00 x10^-14 at 298K

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

how to calculate the pH of strong bases

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

buffer solution is

A

a system that minimises pH changes on addition of small amounts of an acid or base

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

what are the two components of a buffer solution

A

weak acid and its conjugate base

17
Q

what could you add to CH3COOH to make a buffer solution

A

CH3COONa (which dissociates to provide the conjugate base)

or… NaOH (which neutralises some of the weak acid, forming the conjugate base)

18
Q

how do you calculate the pH of a buffer solution?

A

rearrange Ka

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

19
Q

explain the changes that take place when you add an acid to a buffer solution

A

[H+] increases
H+ ions react with conjugate base A-
equilibrium shifts to the left, removing the excess H+ ions

20
Q

explain the changes that take place when you add an alkali to a buffer solution

A

[OH-] increases
H+ + OH- → H₂O
HA dissociates, shifting the equilibrium to the right, increasing [H+]

21
Q

what is the equation for the carbonic acid - hydrogen carbonate buffer system?

A

H₂CO₃ ⇌ H+ + HCO₃-

22
Q

what does the carbonic acid - hydrogen carbonate buffer system control?

A

blood pH

between 7.35-7.45

23
Q

describe and explain the shape of a pH titration curve

A

gradual increase- pH increases very slowly as base is added as acid is in great excess
vertical section - pH increases rapidly with a very small addition of base. Acid and base conc. are v similar
gradual increase - pH increases slowly as basic solution is added, base is in excess

24
Q

what is the equivalence point

A

the volume of one solution that reacts exactly with another solution. The middle of the vertical section of the pH titration curve.

25
why does an indicator change colour?
HA (weak acid) is one colour A- (conjugate base) is another colour colour change indicates endpoint
26
how do you measure pH with a pH meter?
electrode dipped in solution and connected to a meter that displays pH reading.
27
how do you choose an indicator for a reaction?
pH range must coincide with the vertical section of the pH titration curve. Ideally end point = equivalence point.
28
why is no indicator suitable for a weak acid-weak base reaction?
no vertical section