Ionic

Question 1

Why is it difficult to measure the equilibrium constant of strong electrolytes?

Answer 1

The solute is present entirely as ions

Question 2

Why can the equilibrium constant be determined in weak electrolytes?

Answer 2

The solute is incompletely ionised in solution

Question 2

What does the law of mass action predict at equilibrium for a weak electrolyte?

Answer 2

K = [C][D]/[A][B]

Question 3

K value when equilibrium lies to the RHS

Answer 3

K greater than 1

Question 4

K value when equilibrium lies to the LHS

Answer 4

K less than 1

Question 5

[H+] value for acidic solutions

Answer 5

[H+] > 1x10^-7 mol L-1

Question 6

[H+] value for alkaline solutions

Answer 6

[H+] < 1x10^-7 mol L-1

Question 7

Why is the log of [H+] and [OH-] taken?

Answer 7

Molarities vary over many orders of magnitude

Question 8

How is pH related to [H+]?

Answer 8

pH = -log10[H+]

Question 9

What does 1 unit of pH indicate for molarity?

Answer 9

1 unit difference in pH = factor of 10 change in molarity

Question 10

Why can water have a pH of less than 7?

Answer 10

Due to carbon dioxide in the atmosphere dissolving in water to give carbonic acid. Dissociation releases H+ ions and pH drops

Question 11

What is Kw?

Answer 11

Kw = [H+][OH-] = 1x10^-14 mol2L-2

Question 12

What is a Brønsted acid?

Answer 12

A proton donor

Question 13

What is Ka?

Answer 13

The ionisation or dissociation constant for an acid

Question 14

What does the value of Ka indicate?

Answer 14

If Ka is large, acid is strong
If Ka is small, acid is weak

Question 15

What is Kb?

Answer 15

The ionisation or dissociation constant of a base

Question 16

What does the value of Kb indicate?

Answer 16

If Kb is large, base is strong
If Kb is small, base is weak

Question 17

What can pKa be used for?

Answer 17

Expressing strengths of acids and bases using the same term

Question 18

How can pKa be determined using Ka?

Answer 18

pKa = -logKa

Question 19

How can Kb be converted ot Ka?

Answer 19

Ka x Kb = Kw = 1x10-14

Question 20

What does lower Pka indicate about the strength of an acid?

Answer 20

Lower value of pKa indicates a strong acid as the -log is taken

Question 21

What does a lower pKa indicate about the strength of a base?

Answer 21

Lower value of pKa indicates a weak base

Question 22

What is the pH equation using pKa and c for an acid?

Answer 22

pH = 1/2 (pKa - logC)

Question 23

What equation is used to determine pH using pKa and c for a base?

Answer 23

pH = 1/2 (pKw + pKa + logC)

Question 24

What is a reaction between an acid and a base called?

Answer 24

Neutralisation

Question 25

What is a salt?

Answer 25

Any ionic compound formed by neutralisation of an acid with a base

Question 26

What are properties of a salt?

Answer 26

Ionic H2O soluble High melting point Crystalline solid

Question 27

What is a cation?

Answer 27

A positively charged species

Question 28

What is an anion?

Answer 28

A negatively charged species

Question 29

What is hydrolysis?

Answer 29

The breaking of a bond by action of water

Question 30

What characteristics does the conjugate base of a strong acid have?

Answer 30

Weak conjugate base

Question 31

What is an amphiprotic salt?

Answer 31

A salt that can function as both a base and an acid

Question 32

How can the pH of an amphiprotic salt be found?

Answer 32

pH = 1/2 (pKa1 + pKa2)

Question 33

What are buffers?

Answer 33

A mixture of weak acids (or bases) and their salts

Question 34

How do buffers work?

Answer 34

They have reserves of potential acidity or basicity and can nullify the tendency for pH changes (source or sink for protons)

Question 35

How does a buffer of a weak acid and its conjugate base work?

Answer 35

The weak acid can transfer protons to a strong base and the conjugate base can accept protons from a strong acid

Question 36

How does a buffer of a weak base and its conjugate acid work?

Answer 36

The weak base can accept protons from the strong acid and the conjugate acid can transfer protons to a strong base

Question 37

At what pH do buffers work best?

Answer 37

pH = pKa of the acid or base from which they are made

Question 38

What is used for a buffer for pH 7?

Answer 38

The 2nd ionisation of phosphoric acid H3O4 + NaOH

Question 39

Henderson Hasselbach Equation for a weak acid and salt

Answer 39

pH = pKa + log([A-]/[HA]) pH = pKa + log ([SALT]/[ACID])

Question 40

What is the buffer capacity?

Answer 40

β = the number of moles of strong monobasic acid (or monoacidic base) required to produce an increase or decrease of 1 unit on pH scale

Question 41

What is the Buffer Capacity equation?

Answer 41

β = no of moles/change on pH

Question 42

What is a high capacity buffer?

Answer 42

The amount of base present is about 10% or more of the amount of acid (otherwise the base gets used up quickly)

Question 43

What is the effective range of a buffer?

Answer 43

pH = pKa - 1 and pH = pKa +1 So the effective range is ±1

Question 44

What are the 3 main biological buffers?

Answer 44

Dissolved CO2, Dihydrogen phosphate (and its sodium salt) and protein macromolecules

Question 45

What biological buffer is responsible for the most buffering action?

Answer 45

Dissolved CO2 to give carbonic acid and its sodium salt

Question 46

What are zwitterions?

Answer 46

Amphiprotic molecules and in solution both functional groups ionise to form salt

Question 47

What are amino acids?

Answer 47

Zwitterions

Question 48

At what pH are amino acids ionised?

Answer 48

Amino acids are ionised at all pH values

Question 49

Why does the body need to have specialised uptake of amino acids?

Answer 49

Amino acids can't cross the biological membrane by passive diffusion

Question 50

What is the isoelectric point of a protein or amino acid?

Answer 50

When the number of ionised COO- groups = NH3+ the pH = isoelectric point

Question 51

What does pI represent?

Answer 51

The isoelectric point represents the minimum solubility of proteins

Question 52

What is pI useful for?

Answer 52

Used in electrophoresis to separate mixtures of proteins as pI is the point at which migration of protein in an electric field is slowest

Question 53

How can the percentage ionised of an acid be calculated?

Answer 53

F ionised = 1/ 1 + antilog(pKa -pH)

Question 54

How can the percentage ionised of a base be calculated?

Answer 54

F ionised = 1/ 1 + antilog(pH -pKa)

Question 55

If pH = pKa + 1 for an acidic drug, what is the % of drug ionised

Answer 55

90%

Question 56

What functional groups make a drug acidic?

Answer 56

Carboxylic acids and phenol groups

Question 57

What functional groups make a drug basic?

Answer 57

A nitrogen atom with a lone pair of electrons available for bonding

Question 58

Why are amides neutral?

Answer 58

Carbon-Nitrogen bond has double bond character due to resonance

Question 59

Why must basic and acidic drugs not be administered together?

Answer 59

A precipitation of less water soluble free base may occur

Question 60

Why are sulfonamides weakly acidic?

Answer 60

Due to the powerful electron-withdrawing effect of the SO2 and the stabilisation of the anion by resonance

Question 61

What is the equation for multiple extractions?

Answer 61

Wn = W (A/PS+A)^n