Acids and Bases
0.0 / 5
- Created by: LBCW0502
- Created on: 02-12-17 11:18
What is a strong acid?
A substance which completely dissociates in solution to produce hydronium ions
1 of 83
Gives examples of a strong acid (3)
Hydrochloric acid, nitric acid and sulfuric acid (also examples of inorganic acids)
2 of 83
What is a weak acid?
A substance which doesn't dissociate completely in solution to produce hydronium ions (equilibrium formed)
3 of 83
Give examples of a weak acid (4)
Hypochlorous acid, nitrous acid, hydrogen fluoride and hydrogen cyanide
4 of 83
In a reaction between hydrochloric acid and water, what is the conjugate base and what is the conjugate acid produced?
Conjugate base is the chloride ion and the conjugate acid is the hydronium ion
5 of 83
What is the Bronsted-Lowry definition of an acid?
An acid is a proton donor
6 of 83
What is the Bronsted-Lowry definition of an base?
A base is a proton acceptor
7 of 83
In a reaction between water and ibuprofen, what is the conjugate base and what is the conjugate acid?
Ionised ibuprofen (- charge) is the conjugate base and the hydronium ion is the conjugate acid
8 of 83
Give examples of common organic acids (3)
Carboxylic acids, phosphoric acids, sulfonic acids
9 of 83
Give examples of common inorganic bases (4)
Ammonia, sodium hydroxide, sodium acetate, sodium carbonate
10 of 83
Give examples of common organic bases (3)
Primary, secondary and tertiary amines
11 of 83
How is the acidity of an aqueous solution quantified?
Using pH (negative logarithm of hydronium ion concentration)
12 of 83
How does the concentration of hydronium ions affect the value of pH?
The higher the concentration of hydronium ion (the more acidic the solution is) the lower the pH
13 of 83
Describe what happens when acid is added to pure water
Hydronium ion concentration increases, hydroxide ion concentration decreases (neutralisation reaction)
14 of 83
What is the pH of a 1.0 M solution of a strong acid?
0.00
15 of 83
Describe what happens when a base is added to pure water
Increase in hydroxide ions, decrease in hydronium ions (auto-ionisation/neutralisation doesn't go to completion). Able to detect concentration of hydronium ions in a base
16 of 83
What is the pH of a 1.0 M solution of a strong base?
14
17 of 83
How do you search for acidic groups in a structure of an organic (drug) molecule?
Locate functional groups which have the capacity to donate protons
18 of 83
How do you search for basic groups in a structure of an organic (drug) molecule?
Locate functional groups which contain lone pairs of electrons
19 of 83
Give the common acidic groups (3)
Carboxylic acid, sulfonamide and phenol
20 of 83
Give the common basic groups (6)
Primary/secondary/tertiary amines, aromatic/imidazole/pyridine amines
21 of 83
Give examples of acidic drugs (3)
Ibuprofen (analgesic), phenol (antiseptic mouth spray), diclofenamide (anti-epileptic)
22 of 83
Give examples of basic drugs (3)
Chloropromazine (anti-psychotic), atenolol (beta blocker), benzococaine (local anaesthetic)
23 of 83
Give examples of amphoteric drugs (2)
Mesalamine (Inflammatory Bowel Disease drug) and lisinopril (Anti-hypertensive)
24 of 83
How is a drug e.g. Penicillin G (free acid/non-polar) made more soluble in solution?
Use Penicillin G in the form of a potassium salt (more polar)
25 of 83
How is morphine converted to codeine?
OH replaced by CH3 group
26 of 83
How is morphine and codeine separated in the lab?
Separating funnel used. Add NaOH (ionises morphine/codeine remains the same). Morphine in aqueous phase (bottom layer) and codeine in organic phase (top layer)
27 of 83
Which is quinine used to treat?
Malaria
28 of 83
In which form are drug molecules absorbed in the body?
In unionised form
29 of 83
Is drug stability affected by substituents?
Yes - e.g. aspirin reacts with OH to produce hydroxybenzoic acid and acetic acid (reduction in drug stability)
30 of 83
Are acidic and basic groups involved drug pharmacological activity?
Yes e.g. ACE-Lisinopril complex
31 of 83
The equilibrium of a reaction for a strong acid will be in which side?
The right side
32 of 83
How is the position of the equilibrium is expressed quantitatively for an acid?
As the equilibrium dissociation constant (also known as ionisation constant). Ka
33 of 83
What is pKa?
Strength of the acid expressed as the negative logarithm of the acidity constant, Ka
34 of 83
What are the units for Ka?
mol.dm^-3
35 of 83
What are the units for pKa?
No units
36 of 83
How does the strength of the acid affect Ka and pKa?
The stronger the acid, the greater the Ka, the smaller the pKa, the weaker the conjugate base
37 of 83
An acid will donate a proton to a conjugate base of any other acid with a higher or lower pKa?
Higher pKa
38 of 83
Are the products or reactants more stable?
Products are more stable (less reactive)
39 of 83
Which equation shows the relationship between pH and pKa?
The Henderson Hasselbalch Equation
40 of 83
What happens if the pH = pKa?
The concentration of the acid and the conjugate base are equal
41 of 83
A shift in pH by one unit changes the ratio of ionised/unionised forms by a factor of what?
By a factor of 10
42 of 83
What is the pKa of a carboxylic acid?
2-4
43 of 83
What is the pKa of sulfonamide?
8-10
44 of 83
What is the pKa of phenol?
~10
45 of 83
If a functional group has a pKa > 7 does this mean that the group is not acidic?
No
46 of 83
What are the three factors which affect acid strength?
Bond polarisation/inductive effects, resonance/mesomeric effects, hydrogen bonding
47 of 83
What is the inductive effect?
An effect in the bonds due to bond polarisation. Electrons not shared equally due to atoms with opposite charges. Electrons attracted to the most electronegative atom
48 of 83
What is the -I effect?
Effect caused by electron withdrawing groups e.g. NH3+ > NO2 > COOH > Cl > Br > I
49 of 83
What is the +I effect?
Effect caused by electron donating groups e.g. NH2 > OH > CH3 > C6H5
50 of 83
What happens to the pKa when chloride ions are added to acetic acid?
pKa decreases
51 of 83
What is resonance?
Resonance forms differ in the locations of their p and/or non-bonding electrons; they are imaginary, however, and the real structure is a hybrid of the different resonance forms
52 of 83
What is the -M effect?
Resonance involving electron withdrawing groups
53 of 83
What is the +M effect?
Resonance involving electron donating groups
54 of 83
How can resonance be used to determine the most acidic molecule?
The more resonance structures a molecule has, the more acidic it is (and has increased stability)
55 of 83
How does hydrogen bonding affect acidic strength?
Hydrogen bond increases stability of the conjugate base (lower pKa)
56 of 83
How does the strength of a base affect the position of equilibrium?
The stronger the base, the more readily it will gain a proton – the equilibrium of the reaction below is shifted to the right:
57 of 83
How is the position of the equilibrium is expressed quantitatively for a base?
As the equilibrium dissociation constant (also known as ionisation constant). Kb
58 of 83
What is pKb?
The strength of a base expressed by the negative logarithm (to the base 10) of its ionisation constant
59 of 83
What are the units for Kb?
mol.dm^-3
60 of 83
What are the units for pKb?
There are no units
61 of 83
How is a strength of a base quantified using the pKa of its conjugate acid?
pKb = Kw (ionic product of water) - pKa. Kw = [OH-] [H+] where [OH-] and [H+] both equal 10^-7 so Kw = 10^-14 and pKw = 14. pKa = 14 - pKb
62 of 83
How does base strength affect pKb and pKa?
The stronger the base, the lower the pKb and the higher the pKa
63 of 83
What is the pKa for a primary/secondary/tertiary amine?
9-10
64 of 83
What is the pKa for an aromatic amine?
2-4
65 of 83
What is the pKa for imidazole?
6-7
66 of 83
What is the pKa for a pyridine?
~5.5
67 of 83
If the functional group (e.g. imidazole, pyridine) has a pKa greater than 7, does this mean that it is not an acidic group?
No
68 of 83
What are the factors which affect base strength?
Resonance and inductive effect
69 of 83
How do you calculate the percentage ionisation of an acidic drug?
100 / 1 + (antilog (pKa - pH)) e.g. used for COOH, phenol, aromatic ring (% of COO- formed)
70 of 83
How do you calculate the percentage ionisation of a basic drug?
100 / 1 + (antilog (pH - pKa)) e.g. percentage of drug in protonated form (NH3+)
71 of 83
How does the distance of pH from a particular pH affect ionisation of an acidic drug?
The further away the pH is away from the pKa, the more ionisation. Less ionisation is due to a decrease in pH
72 of 83
How does the distance of pH from a particular pH affect ionisation of a basic drug?
The further away the pH is away from the pKa, the less ionisation. More ionisation is due to a decrease in pH
73 of 83
What is an amphoteric compound?
Contains an acidic group and a basic group with pKa values existing as an electrically neutral molecule at a pH that is midway between the two pKa values. pH = 0.5 (pKa1 + pKa2). Isoelectric point
74 of 83
What is a buffer solution?
A solution that resists changes in major pH. An acidic buffer has a pH < 7 and an alkaline buffer has a pH > 7. Effective in limiting changes in pH over a pH range within one log unit of the pKa of the chosen acid or base, e.g. buffer pH = pKa ± 1.0
75 of 83
How is a simple acidic buffer produced?
As a solution of weak acid and one of its salts (Henderson Hasselbalch Equation)
76 of 83
What happens in a buffer solution when a small amount of acid is added?
Increase in concentration of hydronium ions. Large excess of A- ions reacts with hydronium ions to produce weak acid. Position of equilibrium is more to the left. Extra hydronium ions removed from solution (pH remains unchanged)
77 of 83
What happens in a buffer solution when a small amount of base is added?
Increase in concentration of hydroxide ions. Hydroxide ions react with weak acid to produce A- and hydronium ions. Hydroxide ions also react with hydronium ions to produce water. Additional hydroxide ions removed from solution (pH unchanged)
78 of 83
What is the equation used to calculate the pH of an acid buffer solution (e.g. sodium ethanoate and ethanoic acid, pKa 4.76)?
pH = 4.76 + log ([salt]/[acid]) (increase concentration increases buffer capacity/large volumes not effective)
79 of 83
What is the equation used to calculate the pH of an alkaline buffer solution?
pH = pKa - log ([base]/[salt])
80 of 83
What is a universal buffer?
A buffer solution that buffers over a wide pH range. Involve solutions of compounds with several acidic or basic groups with pKa values separated by 2 log units e.g. citric acid - 3 COOHs, pKa values 3.06/4.78/5.40, and citrate buffer pH 2.1 to 6.4
81 of 83
How is pH measured?
Using a combination electrode digital pH meter. Reference electrode and internal electrode gives measurements to indicate pH. H+ cross through bulb membrane
82 of 83
How is a pH meter calibrated?
Put pH meter into buffer solutions of known pH (acidic, neutral, basic) Place in acid, measure, wash, place in alkali, measure (able to measure pH e.g. between 4 and 9.8 for acid, alkali)
83 of 83
Other cards in this set
Card 2
Front
Gives examples of a strong acid (3)
Back
Hydrochloric acid, nitric acid and sulfuric acid (also examples of inorganic acids)
Card 3
Front
What is a weak acid?
Back
Card 4
Front
Give examples of a weak acid (4)
Back
Card 5
Front
In a reaction between hydrochloric acid and water, what is the conjugate base and what is the conjugate acid produced?
Back
Related discussions on The Student Room
Similar Pharmacy resources:
0.0 / 5
0.0 / 5
0.0 / 5
0.0 / 5
0.0 / 5
0.0 / 5
4.5 / 5 based on 2 ratings
0.0 / 5
0.0 / 5
Comments
No comments have yet been made