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Chemistry > AS.3 Acids, Bases And Buffers > Flashcards

AS.3 Acids, Bases And Buffers Flashcards

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1
Q

Acid

A

Proton donor

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2
Q

Base

A

Proton acceptor

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3
Q

Strong acid

A

Proton donor that dissociates fully

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4
Q

Weak acid

A

Proton donor that dissociates partially

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5
Q

Alkali

A

Soluble base that contains OH- ions

Exception -> NH3 + H2O ——> NH4 + + OH-

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6
Q

Acid base pair

A

Two molecules which interconvert between each other with the loss or gain of a proton

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7
Q

Acid base pair example

A

HA + B ————-> A- + HB+

HA - acid 1
A- - base 1
Conjugate

B - base 2
HB+ - acid 2
Conjugate

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8
Q

Acid + metal ( ionic equation )

A

Salt + H2

Na + H+ ———> Na+ + H2

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9
Q

Acid + metal oxide (ionic equation)

A

Salt + water

MgO + 2H+ ————> Mg2+ + H2O

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10
Q

Acid + alkali (ionic equation)

A

Salt and water

OH- + H+ ——-> H2O

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11
Q

Acid and carbonate

A

Salt + water + carbon dioxide

Group I carbonate - soluble
CO3 2- + 2H+ ———-> CO2 + H2O

Group II carbonate - insoluble
MgCO3 + 2H+ ———> Mg2+ + CO2 + H2O

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12
Q

pH equation

A

-log [H+]

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13
Q

[H+] equation

A

10^-pH

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14
Q

pH of strong acids

A

[monobasic acid] = [H+]

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15
Q

pH of weak acids

A

HA <———-> H+ + A-

Ka = [H+] [A-]/ [HA]

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16
Q

Ka approximates

A

[HA] eq = [HA] undissociated
Amount of HA considered constant because equilibrium is so far to left

[H+] = [A-]
assume only source of ions is from dissociation of HA

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17
Q

Rearrange Ka to calculate pH

A

[H+] = square root of (Ka x [HA])

18
Q

pKa

A

-log(Ka)

19
Q

The larger the Ka, the ——- the pKa

A

The larger the Ka, the more dissociated the acid is, therefore the stronger the weak acid

The larger the Ka, the smaller the pKa

The smaller the pKa, more dissociated the acid is and therefore the stronger the weak acid

20
Q

pH of pure water

A

Kw = [H+] [OH-]

21
Q

Kw at 298K

A

1 x 10^ -14

22
Q

Rearranging Kw

A

Square root of Kw = H+

23
Q

pH of a strong base

A

Kw
——— = [ H+]
[NaOH]

Kw = [H+] x [OH-]

[OH-] = [NaOH]

24
Q

Buffer solution

A

A solution that resists the change to its pH despite the addition of small amounts of acid or alkali

25
Q

How to make a buffer - method 1

A

Weak acid + salt of weak acid

CH3COOH + CH3COONa

Don’t react but coexist

26
Q

How to make a buffer - method 2

A

Excess of weak acid + limited amount of alkali

27
Q

Buffer - add small amount of acid

A

Acid introduces more H+

Weak acid equilibrium will oppose this change and shift to left

The CH3COO- reacts with added H+ to restore amount

[H+] maintained and pH remains unchanged

28
Q

Buffer - adding small amount of alkali

A

OH- from alkali will react with H+ ions in the buffer

Weak acid equilibrium will oppose this change and shift to right

Weak acid will dissociate more to restore amount of H+

[H+] maintained and pH remains unchanged

29
Q

Buffer calculation

A

Ka = [H+] [A-]
————-
[A-]

30
Q

Buffers in blood

A

Carbonic acid acts as weak acid

Hydrogencarbonate acts as conjugate base

H2CO3

HCO3-

31
Q

Blood buffers - increase in H+

A

Weak acid equilibrium shifts to left

32
Q

Blood buffers - increase in OH-

A

Removed by reaction with H+ from equilibrium

Equilibrium then shifts to right to restore [H+]

33
Q

Blood buffers - production of more H2CO3

A

Removed by action of enzyme

H2CO3 ——-> H2O + CO2 (aq)
CO2 transported to lungs

CO2 (aq) ————> CO2 (g)

34
Q

Normal blood pH

A

7.35 - 7.45

35
Q

Graph line shape of neutralisation

A

pH increase slightly - large excess of H+

Point of neutralisation - rapid as small conc of H+ remaining is used up and replaced by OH-

36
Q

Selecting suitable indicator

A

Indicator - Very weak acid

Colour change must be within pH range of equivalence point of titration

37
Q

Suitable indicator for SA/SB

A

3———->11

Methyl orange
Phenolphthalein

38
Q

Suitable indicator for WA/SB

A

7 ———> 11

Phenolphthalein only (8.4 - 10)

39
Q

Suitable indicator for SA/WB

A

3————->7

Methyl orange only (2.8 - 4)

40
Q

Suitable indicator for WA/WB

A

No vertical section of curve

No suitable indicator

Chemistry (27 decks)

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