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PL1002 > Ionic > Flashcards

Ionic Flashcards

1
Q

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

A

The solute is present entirely as ions

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2
Q

Why can the equilibrium constant be determined in weak electrolytes?

A

The solute is incompletely ionised in solution

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2
Q

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

A

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

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3
Q

K value when equilibrium lies to the RHS

A

K greater than 1

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4
Q

K value when equilibrium lies to the LHS

A

K less than 1

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5
Q

[H+] value for acidic solutions

A

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

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6
Q

[H+] value for alkaline solutions

A

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

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7
Q

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

A

Molarities vary over many orders of magnitude

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8
Q

How is pH related to [H+]?

A

pH = -log10[H+]

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9
Q

What does 1 unit of pH indicate for molarity?

A

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

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10
Q

Why can water have a pH of less than 7?

A

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

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11
Q

What is Kw?

A

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

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12
Q

What is a Brønsted acid?

A

A proton donor

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13
Q

What is Ka?

A

The ionisation or dissociation constant for an acid

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14
Q

What does the value of Ka indicate?

A

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

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15
Q

What is Kb?

A

The ionisation or dissociation constant of a base

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16
Q

What does the value of Kb indicate?

A

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

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17
Q

What can pKa be used for?

A

Expressing strengths of acids and bases using the same term

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18
Q

How can pKa be determined using Ka?

A

pKa = -logKa

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19
Q

How can Kb be converted ot Ka?

A

Ka x Kb = Kw = 1x10-14

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20
Q

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

A

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

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21
Q

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

A

Lower value of pKa indicates a weak base

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22
Q

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

A

pH = 1/2 (pKa - logC)

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23
Q

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

A

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

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24
Q

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

A

Neutralisation

25
Q

What is a salt?

A

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

26
Q

What are properties of a salt?

A

Ionic
H2O soluble
High melting point
Crystalline solid

27
Q

What is a cation?

A

A positively charged species

28
Q

What is an anion?

A

A negatively charged species

29
Q

What is hydrolysis?

A

The breaking of a bond by action of water

30
Q

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

A

Weak conjugate base

31
Q

What is an amphiprotic salt?

A

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

32
Q

How can the pH of an amphiprotic salt be found?

A

pH = 1/2 (pKa1 + pKa2)

33
Q

What are buffers?

A

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

34
Q

How do buffers work?

A

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

35
Q

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

A

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

36
Q

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

A

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

37
Q

At what pH do buffers work best?

A

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

38
Q

What is used for a buffer for pH 7?

A

The 2nd ionisation of phosphoric acid H3O4 + NaOH

39
Q

Henderson Hasselbach Equation for a weak acid and salt

A

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

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

40
Q

What is the buffer capacity?

A

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

41
Q

What is the Buffer Capacity equation?

A

β = no of moles/change on pH

42
Q

What is a high capacity buffer?

A

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

43
Q

What is the effective range of a buffer?

A

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

44
Q

What are the 3 main biological buffers?

A

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

45
Q

What biological buffer is responsible for the most buffering action?

A

Dissolved CO2 to give carbonic acid and its sodium salt

46
Q

What are zwitterions?

A

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

47
Q

What are amino acids?

A

Zwitterions

48
Q

At what pH are amino acids ionised?

A

Amino acids are ionised at all pH values

49
Q

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

A

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

50
Q

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

A

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

51
Q

What does pI represent?

A

The isoelectric point represents the minimum solubility of proteins

52
Q

What is pI useful for?

A

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

53
Q

How can the percentage ionised of an acid be calculated?

A

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

54
Q

How can the percentage ionised of a base be calculated?

A

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

55
Q

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

A

90%

56
Q

What functional groups make a drug acidic?

A

Carboxylic acids and phenol groups

57
Q

What functional groups make a drug basic?

A

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

58
Q

Why are amides neutral?

A

Carbon-Nitrogen bond has double bond character due to resonance

59
Q

Why must basic and acidic drugs not be administered together?

A

A precipitation of less water soluble free base may occur

60
Q

Why are sulfonamides weakly acidic?

A

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

61
Q

What is the equation for multiple extractions?

A

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

PL1002 (6 decks)

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