Acid-Base Flashcards
1
Q
At what point does an Indicator change colour?
A
When the pH of the solution changes past the pKa of the indicator
2
Q
How are weak bases defined?
A
Weak bases are defined as having a low Kb
3
Q
How are strong acids defined?
A
Strong acids are defined fully ionising/dissociating (Ka > 1)
4
Q
How does the Brønsted-Lowry model define an acid and a base?
A
Acid as any species that can donate protons (H+). Bases as any species that accept protons (H+)
5
Q
How are strong bases defined?
A
Strong bases are defined as having a high Kb
6
Q
How do we calculate concentration?
A
C = n / v
7
Q
How are the acid and its conjugate base different in indicators?
A
They are different colours
8
Q
How do we calculate Kw?
A
Kw = Ka x Kb
9
Q
How are weak acids defined?
A
Weak acids are defined as having a Ka < 1
10
Q
How do you calculate Ka?
A
Ka = [H3O+] X [A-] / [HA]
11
Q
How do you calculate Kb?
A
Kb = [BH+ ] x [OH-] /
[B]
12
Q
How often should a titration be performed?
A
Until you have obtained three titres that differ by less than or equal to 0.1mL
13
Q
How is the [H+] calculated?
A
[H+ ]= 10^(-pH)
14
Q
Identify the conjugate acid produced in this reaction: NH4+ + OH- ⇌ NH3 + H2O
A
H2O
15
Q
How is [OH-] calculated?
A
[OH-] can be obtained using the pH or pOH value: pH + pOH = 14 pOH = 14 - pH pOH= –log10 [OH- ] [OH-] = 10^(-pOH)
16
Q
Identify the conjugate base produced in this reaction: NH4+ + OH- ⇌ NH3 + H2O
A
NH3
17
Q
How is pH calculated?
A
The pH of a solution can be calculated from the concentration of hydrogen ions using the relationship
pH = -log10 [H+ ]
18
Q
If an acid or a base completely ionises in water what is it called?
A
Strong acid or base
19
Q
How is pOH calculated?
A
pOH = -log10 [OH-]
20
Q
If an acid or a base only partially ionises in water what is it called?
A
A weak acid or base
21
Q
Is a base strong or weak if its pKb is large?
A
Weak
22
Q
Name an example of a monoprotic acid
A
HCl - hydrochloric acid
HBr - hydrogen bromide
HNO3 - nitric acid
CH3COOH - ethanoic acid
22
Q
Is an acid strong or weak if it has a low pKa?
A
Strong
22
Q
Is Kw temperature dependent?
A
Yes
22
Name an example of a triprotic acid
H3PO4 - Phosphoric acid
22
pH + pOH = ?
14 or Kw (at just below 25oC)
22
The strength of an acid is explained by the degree of ...
dissociation of the acid at equilibrium in an aqueous solution
22
Is the conjugate base of a weak acid, stronger or weaker?
Stronger
23
Name an example of a diprotic acid
H2SO4 - sulphuric acid
H2CO3 - carbonic acid
23
Under what circumstances could the numerical value of Kw differ?
Different temperatures. Kw is 10-14 at just below 25oC
23
What are acid-base indicators?
Weak acids or bases, which dissociate slightly in water and form ions
24
What can be tested experimentally to determine the strength of an acid or base?
The electrical conductivity of the acid or base
24
What are examples of Strong Acids?
Hydrochloric Acid (HCl)
Nitric Acid (HNO3)
Sulfuric Acid (H2SO4)
24
What does amphiprotic mean?
A molecule or ion that can donate of accept a proton. Therefore it acts as both an acid and a base.
24
What are examples of Strong Bases?
All group 1 hydroxides (LiOH, NaOH, KOH, RbOH, CsOH) Barium hydroxide (Ba(OH)2)
25
What does it mean if an acid is concentrated?
It means it has a large number of moles of the acid in a litre of water
26
What are examples of Weak Acids?
Carboxylic acid (R-C(=O)-OH), carbonic acid (H2CO3), aqueous carbon dioxide (CO2 (aq))
27
What does it mean if an acid is dilute?
It means it has a small number of moles of the acid in a litre of water
28
What are examples of Weak Bases?
Ammonia (NH3), amines
29
What does Ka represent?
The equilibrium constant for the dissociation of an acid in an aqueous solution
30
What does the buffer region look like on a weak acid or base titration curve?
It is the (almost) horizontal area that occurs before the equivalence point.
31
What is a conjugate acid?
An acid formed when a base accepts an H+
32
What happens when the pH of a solution is equal to the pKa of an indicator?
The indicator will change colour
33
What is a conjugate acid?
An acid formed when a base accepts a proton (H+) B: + H2O → B:H+ + OH- (B:H+ is the conjugate
acid)
34
What impact does having water in the burette have in a titration?
It will decrease the concentration of the titrant and therefore a greater volume will be needed to neutralise the analyte
35
What is a conjugate base?
A base formed by removing a proton (H+) from an acid
36
What impact does having water in the flask holding the analyte have in a titration?
No impact as the number of moles of the substance remains the same
37
What is a conjugate base?
A base formed by removing a proton (H+) from an acid
38
What is a buffer solution?
A solution that resists changes in pH when small quantities of acids or bases are added to it
39
What is a conjugate pair?
Two species that differ by a proton (H+)
40
What is an indicator?
A chemical substance that changes colour at
particular pH values
40
What is a diprotic acid?
An acid that can donate two protons per molecule
41
What is a monoprotic acid?
An acid that can donate one proton per molecule
42
What is a polyprotic acid?
An acid that can donate more than one proton per molecule
43
What is an aliquot?
A fixed volume of liquid measured by a pipette
43
What is a titration?
A technique used to determine the unknown concentration of a solution
44
What is an amphiprotic substance?
A substance that can act as either an acid or a base
45
What is hydronium?
H3O+
45
What is an example of a common amphiprotic
substance?
Examples could include - water, amino acids and hydrogen carbonate ions (HCO3-)
46
What is Kw?
Kw is the ionic product constant of water. It is the equilibrium constant for the self-ionisation of water. Kw can be used to calculate the concentration of
hydrogen ions from the concentration of hydroxide ions in a solution
46
What is pKb a measure of?
The strength of a base
46
What is meant by a standard solution in a titration?
A solution whose concentration is accurately known
47
What is meant by the "strength" of an acid or a base
The level of dissociation that occurs in the acid or base.
48
What is self-ionisation of water?
Self-ionisation of water refers to the reaction in which a water molecule loses a hydrogen ion (leaving OH-)
and the hydrogen ion immediately reacts with another water molecule to form a hydronium ion (H3O+ )
49
What is parallax error?
When the volume of a liquid is read when the eye level is above or below the meniscus. It leads to inaccurate volumes being determined
49
What is the analyte?
The solution in a titration whose concentration is unknown
49
What is pH?
pH is a figure expressing the acidity or alkalinity of a
solution on a logarithmic scale
49
What is the Bronsted-Lowry definition of an acid?
A proton donor
49
What is pKa a measure of?
The strength of an acid
50
What is the Bronsted-Lowy definition of a base?
A species that accepts protons
51
What is the buffer point on a weak acid or weak base titration curve?
It is the point where pH = pKa. It is at half the equivalence volume.
52
What is the definition of a strong acid in terms
of its Ka?
Ka > 1 is a strong acid
53
What is the conjugate acid of hydroxide (OH-)?
H2O
54
What is the definition of a strong base in terms of its Kb?
High Kb - Strong bases
55
What is the conjugate acid of the following base: OH-?
H2O
56
What is the definition of a weak acid in terms of its Ka?
Ka < 1 Weak acids
57
What is the conjugate base of ammonium (NH4+)?
NH3
58
What is the conjugate base of CH3COOH?
CH3COO
58
What is the definition of a weak base in terms of its Kb?
Low Kb - Weak bases
59
What is the dissociation expression for a base?
Kb = [products] / [reactants]
60
What is the dissociation expression for an acid?
Ka = [H+] [A-] / [HA]
61
What is the "end point"?
The point in a titration when the indicator changes colour
62
What strength is an acid or base that is used as an indicator?
They are weak acids and bases
63
What substances make up a buffer?
A weak acid and its conjugate base or a weak base and its conjugate acid
64
What is the equivalence point?
The point in a titration when neutralisation is reached (i.e. when moles H+ = moles OH-)
65
What substance states are included in a dissociation expression?
Aqueous (aq)
66
What is the relationship between the pH range of an acid-base indicator and its pKa value?
A higher pKa correlates to a higher end point of the indicator
67
What type of substance does this equation represent? BOH → B+ (aq) + OH-(aq)
A strong base
68
What is the titrand?
The solution in a titration whose concentration is known
69
What type of substance does this indicator represent? HIn ⇌ H+ (aq) + In-(aq)
A weak acid
70
What type of substance has a pH of 1?
A strong acid
71
Which have better electrical conductivity, strong or weak acids (or bases)?
Strong acids (or bases)
72
What type of substance has a pH of 7?
A neutral substance
72
Why are acids and bases good electrolytes?
They can dissociate into positive and negative ions
which means they can conduct an electrical charge
73
What type of substance has a pH of 13?
A strong base
74
Why is water a weak electrolyte?
It can self-ionise, but equilibrium lies to the left H2O ⇌ H+(aq) + OH-(aq)
75
When choosing an indicator for a titration what are you looking for?
An indicator whose end point is close to the equivalence point.
76
Which Acid and Bases (strong or weak) completely ionise in water?
Strong acids and bases
