Unit 3- Acids and Bases 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 strong acids defined?
A
Strong acids are defined as fully ionising/dissociating (Ka > 1)
3
Q
How are strong bases defined?
A
Strong bases are defined as having a high Kb
4
Q
How are the acid and its conjugate base different in indicators
A
They are different colours
5
Q
How are weak acids defined?
A
Weak acids are defined as having a Ka < 1
6
Q
How are weak bases defined?
A
Weak bases are defined as having a low Kb
7
Q
How does the Brønsted-Lowry model define acid and a base?
A
Acids as any species that can donate protons (H+). Bases as any species that accept protons (H+)
8
Q
How do we calculate concentration?
A
C=n/V
9
Q
How do we calculate Kw?
A
Kw = Ka x Kb
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 is [H+ ] calculated?
A
[H+ ]= 10^(-pH)
13
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)
14
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+ ]
15
Q
How is pOH calculated?
A
pH = -log10 [OH-]
16
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
17
Q
Identify the conjugate acid produced in this reaction: NH4+ + OH- ⇌ NH3 + H2O
A
H2O
18
Q
Identify the conjugate base produced in this reaction: NH4+ + OH- ⇌ NH3 + H2O
A
NH3
19
Q
If an acid or a base completely ionises in water what is it called?
A
Strong acid or base
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
Is an acid strong or weak if it has a low pKa?
A
Strong
23
Q
Is Kw temperature dependent?
A
Yes
24
Q
Is the conjugate base of a weak acid, stronger or weaker?
A
Stronger
25
Name an example of a diprotic acid
H2SO4 - sulphuric acid
H2CO3 - carbonic acid
26
Name an example of a monoprotic acid
HCl - hydrochloric acid
HBr - hydrogen bromide
HNO3 - nitric acid
CH3COOH - ethanoic acid
27
Name an example of a triprotic acid
H3PO4 - Phosphoric acid
28
pH + pOH = ?
14 or Kw (at just below 25oC)
29
The strength of an acid is explained by the degree of ...
dissociation of the acid at equilibrium in an aqueous solution
30
Under what circumstances could the numerical value of Kw differ?
Different temperatures. Kw is 10-14 at just below 25oC
31
What are acid-base indicators?
Weak acids or bases, which dissociate slightly in water and form ions
32
What are examples of Strong Acids?
Hydrochloric Acid (HCl)
Nitric Acid (HNO3)
Sulfuric Acid (H2SO4)
33
What are examples of Strong Bases?
All group 1 hydroxides (LiOH, NaOH, KOH, RbOH, CsOH) Barium hydroxide (Ba(OH)2)
34
What are examples of Weak Acids?
Carboxylic acid (R-C(=O)- OH), carbonic acid (H2CO3), aqueous carbon dioxide (CO2 (aq))
35
What are examples of Weak Bases?
Ammonia (NH3), amines
36
What can be tested experimentally to determine the strength of an acid or base?
The electrical conductivity of the acid or base
37
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.
38
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
39
What does it mean if acid is diluted?
It means it has a small number of moles of the acid in a litre of water
40
What does Ka represent?
The equilibrium constant for the dissociation of an acid in an aqueous solution
41
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.
42
What happens when the pH of a solution is equal to the pKa of an indicator?
The indicator will change colour
43
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
44
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
45
What is a buffer solution?
A solution that resists changes in pH when small quantities of acids or bases are added to it
46
What is a conjugate acid?
An acid formed when a base accepts an H+
47
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)
48
What is a conjugate base?
A base formed by removing an H+ from an acid
49
What is a conjugate pair?
Two species that differ by a proton (H+)
50
What is a diprotic acid?
An acid that can donate two protons per molecule
51
What is a monoprotic acid?
An acid that can donate one proton per molecule
52
What is an aliquot?
A fixed volume of liquid measured by a pipette
53
What is an amphiprotic substance?
A substance that can act as either an acid or a base
54
What is an example of a common amphiprotic substance?
Examples could include - water, amino acids and hydrogen carbonate ions (HCO3- )
55
What is an indicator?
A chemical substance that changes colour at particular pH values
56
What is a polyprotic acid?
An acid that can donate more than one proton per molecule
57
What is a titration?
A technique used to determine the unknown concentration of a solution
58
What is hydronium?
H3O+
59
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
60
What is meant by a standard solution in a titration?
A solution whose concentration is accurately known
61
What is meant by the "strength" of an acid or a base
The level of dissociation that occurs in the acid or base.
62
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
63
What is pH?
pH is a figure expressing the acidity or alkalinity of a solution on a logarithmic scale
64
What is pKa a measure of?
The strength of an acid
65
What is pKb a measure of?
The strength of a base
66
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+ )
67
What is the analyte?
The solution in a titration whose concentration is unknown
68
What is the Bronsted- Lowry definition of an acid?
A proton donor
69
What is the Bronsted- Lowy definition of a base?
A species that accepts protons
70
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.
71
What is the conjugate acid of hydroxide (OH- )?
H2O
72
What is the conjugate acid of the following base: OH- ?
H2O
73
What is the conjugate base of ammonium (NH4+)?
NH3
74
What is the conjugate base of CH3COOH?
CH3COO-
75
What is the definition of a strong acid in terms of its Ka?
Ka > 1 is a strong acid
76
What is the definition of a strong base in terms of its Kb?
High Kb - Strong bases
77
What is the definition of a weak acid in terms of its Ka ?
Ka < 1 Weak acids
78
What is the definition of a weak base in terms of its Kb?
Low Kb - Weak bases
79
What is the dissociation expression for a base?
Kb = [products] / [reactants]
80
What is the dissociation expression for an acid?
Ka = [H+] [A-] / [HA]
81
What is the "end point" ?
The point in a titration when the indicator changes colour
82
What is the equivalence point?
The point in a titration when neutralisation is reached (i.e. when moles H+ = moles OH-)
83
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
84
What is the titrand?
The solution in a titration whose concentration is known
85
What strength is an acid or base that is used as an indicator?
They are weak acids and bases
86
What substances make up a buffer?
A weak acid and its conjugate base or a weak base and its conjugate acid
87
What substance states are included in a dissociation expression?
Aqueous (aq)
88
What type of substance does this equation represent? BOH → B+ (aq) + OH-(aq)
A strong base
89
What type of substance does this indicator represent? HIn ⇌ H+ (aq) + In-(aq)
A weak acid
90
What type of substance has a pH of 1?
A strong acid
91
What type of substance has a pH of 7?
A neutral substance
92
What type of substance has a pH of 13?
A strong base
93
When choosing an indicator for a titration what are you looking for?
An indicator whose end point is close to the equivalence point.
94
Which Acid and Bases (strong or weak) completely ionise in water?
Strong acids and bases
95
Which have better electrical conductivity, strong or weak acids (or bases)?
Strong acids (or bases)
96
Why are acids and bases good electrolytes?
They can dissociate into positive and negative ions which means they can conduct an electrical charge
97
Why is water a weak electrolyte?
It can self-ionise, but equilibrium lies to the left H2O ⇌ H+(aq) + OH-(aq)
