Block 5 - Acids and Bases Flashcards

Question

Acidity - charge stabilisation by inductive effects

Answer 1

Presence of nearby electronegative atoms / EWGs move charge away from acidic H --> -H bonds weaker --> stronger acid

Answer 2

Allows charge to be spread out over a large number of atoms | Can occur through resonance

Answer 3

Make the conjugate base as stable as possible

Answer 4

pH < pKa : more acid form (HA) pH = pKa : HA and A- in equal conc pH > pKa : more base form (A-)

Answer 5

``` Have 2 (or 3 respectively) pKa values - one for loss of first proton, and one for loss of second pKa increases (i.e. pKa1 < pKa2) ```

Answer 6

NH2CHRCO2H | where R defines the amino acid

Answer 7

Amine group: -NH2 (conjugate acid -NH3+) | Carboxyl group: -CO2H (conjugate base -CO2-)

Answer 8

The point at which the zwitterion for amino acids has max conc

Answer 9

Allows separation of mixtures of amino acids by their charge

Answer 10

For acids and bases, the normal situation is that a max of two species exist significantly in any conditions

Answer 11

Within 1 pH unit (+/- 1) of the pKa of the acid form

Answer 12

If pH < pKa, exists as acidic form (NH3 or COOH) If pH > pKa, exists as basic form (NH2 or COO-) If pH = pKa, exists as acidic and basic form (mixture)

Answer 13

Only the strong acid contributes to [H3O+] | This is not true if pH > 6

Answer 14

Only the strong base contributes to [OH-] | This is not true if pH < 8

Answer 15

Weak acid --> doesn't dissociate to large extent --> dominant species is acid form --> pH < pKa

Answer 16

1. The only source of H3O+ is from the dissociation, so [conjugate base] = [H3O+] 2. The dissociation is small compared to the original amount, so [HA] = [HA]0 - [conjugate base] ≈ [HA]0

Answer 17

1. pH more than 1 below 7 2. pH more than 1 below pKa 3. Check pH is on acid side of pKa: pH < pKa

Answer 18

Weak base --> base form dominates --> pH > pKa

Answer 19

1. The only source of OH- is from the reaction, so [conjugate acid] = [OH-] 2. The amount of reaction is small compared to the original amount, so [base] = [base]0 - [conjugate acid] ≈ [base]0

Answer 20

1. pH is more than 1 above 7 2. pH is more than 1 above pKa 3. pH is on base side of pKa: pH > pKa

Answer 21

Relevant ones where species of interest is involved in equation Expect pH between pKas of relevant equations

Answer 22

[H3O+] and [OH-] are much less than the conc of the amphoteric species, so the only reaction the amphoteric species undergoes is with itself

Answer 23

[H3O+] << original conc

Answer 24

Can only use for buffers!! Extent of dissociation of weak acid and its conjugate base is small, so [HA] = [HA]initial and [A-] = [A-]initial When HA and A- are of similar conc, the log term is small and pH is approx equal to pKa and will only change by +/- unit

Answer 25

Solution where pH changes much less than that of pure water when acid or base is added, i.e. resists changes in pH Typically contain either equal amounts of a weak acid and its conjugate base (where buffer pH < 7) or equal amounts of a weak base and its conjugate acid (where buffer pH > 7)

Answer 26

It contains both species that can accept protons (to react with added acids) and that can donate protons (to react with added base)

Answer 27

When [HA] is close to [A-], i.e. most suitable at pH around pKa of the acid More effective with higher conc of the two species as there is more to react with added acid or base

Answer 28

It has exceeded its capacity, and pH will change significantly

Answer 29

pH changes significantly

Answer 30

pH changes significantly

Answer 31

Doesn't change (much)

Answer 32

pH of solution changes by a small amount

Answer 33

A method of volumetric analysis for determining conc of an unknown solution by letting it react with another whose conc is known

Answer 34

Volume at which the reaction is just completed

Answer 35

Before any acid is added, pH is high As acid is added, pH of solution falls, gradually at first, then faster as equivalence point is approached After EP, rate of pH change slows Well beyond the EP, pH is low Since acid and base are strong, both 100% dissociated and pH at EP is 7

Answer 36

pKa of acid

Answer 37

Beginning of titration, weak acid only pH rises fairly steeply when first drops of base are added - only little OH- required to react with free H3O+ Buffer region - pH changes slowly Half-equivalence point - reaction is half complete, so there are equal amounts of acid and base present Equivalence point - reaction is 100% complete, only conjugate base present --> pH > 7 After EP when all acid has been deprotonated, solution is essentially a strong base and curve flattens out; pH determined by strong base

Answer 38

pH = pKa Can only work out pKa for weak acid/base involved in titration, not strong acid/base, as no equilibrium between conjugate acid and base for strong acids/bases so at 1/2 equivalence point, pH only determined by amount of unreacted acid present, not due to an equilibrium

Answer 39

Beginning of titration - weak base only Buffer region - pH changes slowly Half-equivalence point - reaction is half complete, so there are equal amounts of acid and base present Equivalence point - reaction is 100% complete; only conjugate acid present; pH < 7 After EP when all base has been protonated, solution is strong acid and curve flattens out; pH determined by strong acid

Answer 40

When we decide to stop, generally because observable change has occurred Ideally, end point is at equivalence point

Answer 41

Compounds that are diff colours in their acid and base forms, i.e. they are acids or bases too Colour change occurs around at pH around pK(In) pK(In) should be around 1 pH unit of pH of equivalence point

Answer 42

Multiple equivalence points and buffer regions

Block 5 - Acids and Bases Flashcards

(66 cards)