C1 Acid-base chemistry 1

Question 1

physicochemical modes of action for dyspepsia

Answer 1

antacids
raft-forming agents
anti-foaming agents

Question 2

pharmacological modes of action for dyspepsia

Answer 2

H2 receptor antagonists
proton pump inhibitors

Question 3

main chemical bases of treatment

Answer 3

• reduced acidity in the stomach (physicochemical and pharmacological modes of action)
• prevention of acid reflux (physicochemical mode of action)

Question 4

simply describe the mode of action of antacids

Answer 4

consume acid by use of a base

Question 5

describe magnesium hydroxide as an antacid giving its balanced equation with hydrochloric acid

Answer 5

Mg(OH)2 + 2HCl -> MgCl2 + 2H2O

• consume stomach acid
• products formed are not acidic or basic
• neutralisation

Question 6

Arrhenius definition of an acid

Answer 6

a substance that increases the concentration of H+ when dissolved in water

Question 7

arrhenius definition of a base

Answer 7

a substance that increases the concentration of OH- when dissolved in water

Question 8

Bronsted-Lowry definition of an acid

Answer 8

a proton donor

Question 9

Bronsted-Lowry definition of an base

Answer 9

a proton acceptor

Question 10

describe Bronsted-Lowry definitions in general

Answer 10

• more general
• should always use these definitions in aqueous solutions

Question 11

what occurs in an acid-base reaction?

Answer 11

a proton is transferred from acid to base

Question 12

how do protons exist in water?

Answer 12

• not independently
• attach strongly to water to form hydronium ions

Question 13

describe and explain the deionisation of hydrochloric acid in water. give the chemical equation

Answer 13

• essentially 100% of the HCl dissolved in water ionises to the hydronium and chloride ions (one-headed arrow)
• I.e. HCl transfers all of its protons and the reaction goes to completion
• HCl is a strong acid

Question 14

describe and explain the deionisation of acetic acid in water. give the chemical equation

Answer 14

• only a proportion of its protons are transferred to water
• I.e. the reaction is considered an equilibrium (equilibrium arrow required)
• acetic acid is a weak acid

Question 15

describe strong acids

Answer 15

• fully ionise in aqueous solutions
• transfer all their protons to water in aqueous solutions
• reactions go to completion

Question 16

describe weak acids

Answer 16

• partially ionise in aqueous solutions
• don’t transfer all their protons to water in aqueous solutions
• reactions are equilibria

Question 17

what do equilibrium constant values (Ka) provide?

Answer 17

quantitative indication of whether an acid is strong or weak

Question 18

define conjugate acid

Answer 18

the acid (proton donor) on the product side of the reaction

Question 19

define conjugate base

Answer 19

the base (proton acceptor) on the product side of the reaction

Question 20

what do conjugate acid / base pairs differ by?

Answer 20

just a proton

Question 21

what are all of these?

Answer 21

conjugate acid / base pairs

Question 22

does water behave as an acid or a base?

Answer 22

• both
• a small amount of water molecules are ionised in water
• one water molecule can act as an acid if another acts as a base (this produces one hydroxide ion and one hydronium ion)

Question 23

if 2 water molecules become ionised to produce a hydroxide ion and a hydronium ion, which is the conjugate acid and which is the conjugate base?

Answer 23

• hydronium ion is the conjugate acid
• hydroxide ion is the conjugate base

Question 24

equation for K (equilibrium constant) of this general acid dissociation equation

Answer 24

Question 25

what can the general acid dissociation equation for K (shown in the image) be simplified to and what does this turn the equation into?

Answer 25

- since [H2O] can be considered constant in aqueous solutions, it can be taken out - this makes K = Ka (acid dissociation constant)

Question 26

what does the magnitude of Ka indicate?

Answer 26

a quantitative measure of acid strength

Question 27

compare HCl (Ka = 10^7) and ethanoic acid (Ka = 1.76 x 10^-5) in terms of their Ka and equilibriums

Answer 27

HCl - equilibrium lies far to the right - A- is favoured over HA - strong acid CH3COOH - equilibrium lies to the left - HA is favoured over A- - weak acid

Question 28

why is pKa often used over Ka?

Answer 28

- pKa helps to avoid very small and very large numbers being used - gets rid of lots of decimal places

Question 29

describe the Ka and pKa values of strong acids

Answer 29

large Ka small pKa

Question 30

describe the Ka and pKa values of weak acids

Answer 30

small Ka large pKa

Question 31

general formula for K for base dissociation and Kb

Answer 31

Question 32

how is the strength of a base described?

Answer 32

- in terms of the pKa of its conjugate acid

Question 33

describe Ka and pKa values of strong bases

Answer 33

- small Ka - large pKa - the larger the pKa of the conjugate acid of the base, the stronger the base - BH+ favoured over B

Question 34

describe Ka and pKa values of weak bases

Answer 34

- large Ka - small pKa - the smaller the pKa of the conjugate acid of the base, the weaker the base - B favoured over BH+

Question 35

what is Kw? describe how this is derived from Ka and Kb formulae

Answer 35

- ionisation constant for water - Ka x Kb

Question 36

what does the equation of Kw confirm about the strength of bases and conjugate acids?

Answer 36

- concentration of hydronium and hydroxide ions multiplied is the ionisation constant for water (Kw) - this is seen after cancelling out common components in fractions - this confirms that a STRONG BASE WILL HAVE A WEAK CONJUGATE ACID

Question 37

what is the Kw of pure water at 25 degrees C?

Answer 37

10^-14

Question 38

what is pKw?

Answer 38

14

Question 39

pH of pure water at 25 degrees C

Answer 39

7

Question 40

when does the pH of neutrality vary?

Answer 40

with temperature

Question 41

how does the degree of ionisation of water change with temperature?

Answer 41

- degree of ionisation of water increases with temperature - hence, the pH of neutrality decreases

Question 42

pH of neutrality at 37 degrees C

Answer 42

6.8