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Chemistry > 6 Acids, bases and pH > Flashcards

6 Acids, bases and pH Flashcards

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1
Q

State the Arrhenius definition of an:

a) ‘acid’
b) ‘base’

A

a) = produces H⁺ when dissolved in water

b) = produces OH- and a cation in aqueous solution

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2
Q

State the Bronstead-Lowry definition of an:

a) ‘acid’
b) ‘base’

A

a) H⁺ donor

b) H⁺ acceptor

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3
Q

State the Lewis definition of an:

a) ‘acid’
b) ‘base’

A

a) an electron-pair acceptor

b) an electron-pair donor

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4
Q

Why do acids form hydrogen ions (H⁺)?

A

the only positively-charged ion when dissolved in water

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5
Q

What are the three properties of hydrogen ions?

A

proton (H⁺) donor
lone-pair acceptor
pH < 7

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6
Q

Define ‘strong acids.’ Give an example.

A

= are completely dissociated to ions in solution
i.e. hydrochloric acid
HCl → H⁺ + Cl-

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7
Q

Define ‘weak acids.’ Give an example.

A

= are incompletely dissociated in solution
i.e. carbonic acid
H₂CO₃ ⇌ H⁺ + HCO₃- ⇌ 2H⁺ + CO₃2-

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8
Q

What do both bases and alkalis both do? Give 2 examples of equations of this.

A

both form hydroxide ions when dissolved in water
NaOH → Na⁺(aq) + OH- (aq)
NH₃ + H₂O ⇌ NH₄⁺ (aq) + OH-(aq)

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9
Q

What are the four properties of hydroxide ions?

A

proton (H⁺) acceptor
lone-pair donor
pH > 7
slippery feel

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10
Q

State the 2 definitions of an ‘alkali.’

A

forms hydroxide ions as the only negatively-charged ions when dissolved in water (e.g. NaOH)
a basic salt alkali metal or alkaline earth metal

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11
Q

Define ‘neutralisation.’

A

acid + base → salt + water

i. e. HCl + NaOH → H₂O + NaCl
overall: H⁺ + OH- → H₂O

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12
Q

Define ‘strong base.’

A

= H⁺ ion of the acid combines with the OH- of the base to form water

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13
Q

Define ‘salt.’

A

= the compound formed by the cation of the base and the anion of the acid (H⁺ of acid replaced by metal ion)

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14
Q

Give 2 examples of an acid-base neutralisation reaction and state the lone pair donor and lone pair acceptor reactions.

A 
NH₃        +    HCl →   NH₄⁺Cl-
lone pair    lone pair
donor         acceptor 
NH₃        +    BF₃ →  NH₃⁺BF₃-
lone pair    lone pair
donor         acceptor
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15
Q

How are acids related to bases?

A

Acid ⇌ proton + conjugate base

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16
Q

How are bases related to acids?

A

Base ⇌ proton + conjugate acid

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17
Q

Label the conjugate acid-base pairs [as pairs (1) and (2)] in the following neutralisation reaction.

H₂CO₃ + OH- →

A

H₂CO₃ + OH- → HCO₃- + H₂O
(1) acid base(1) conjugate conjugate (2)
base (1) acid

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18
Q

Label the conjugate acid-base pairs [as pairs (1) and (2)] in the following neutralisation reaction.

CH₃COOH + H₂O ⇌

A

CH₃COOH + H₂O ⇌ CH₃COO- + H₃O⁺

(1)acid (2)base (1)base (2)acid

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19
Q

What is meant by acid strength?

A

not the same as concentration
strong = full dissociation
weak = partial dissociation

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20
Q

How is acid strength quantified?

A

by the acid dissociation constant, Ka

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21
Q

State the formula for Ka and how it is derived.

A 
General acid-base reaction:
HA + H₂O ⇌  H₃O⁺ + A-
Therefore:
Ka = [H₃O⁺][A-]/[HA][H₂O]
Ignore [H₂O] as it is very large and not changed significantly during the reaction:
Ka = [H₃O⁺][A-]/[HA]
Or better known as:
Ka = [H⁺][A-]/[HA]
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22
Q

State the formula for Kb and how it is derived.

A 
General acid-base reaction:
B + H₂O ⇌  BH + OH-
Therefore:
Ka = [BH][OH-]/[B][H₂O]
Ignore [H₂O] as it is very large and not changed significantly during the reaction:
Ka = [BH][OH-]/[B]
Or better known as:
Kb = [B⁺][OH-]/[B]
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23
Q

How does the value of Ka/Kb correspond to the strength of an acid/base?

A

The larger the value the stronger the acid/base

24
Q

Define ‘pH.’

A

a measure of the concentration of H⁺

25
Q

What is pH usually measured by?

A

by an indicator or using a pH probe

26
Q

What is pH usually exist as and how is this converted?

A

It is a very small value in most cells

The p scale converts this to a whole number

27
Q

State the formula for pH.

A

pH = -log10[H⁺]

28
Q

What is pH of 6 equivalent to?

A

a H⁺ concentration of 1.00x10^-6M

29
Q

State the formula for pOH and what it measures.

A

pOH = -log10[OH-]

It measures basicity

30
Q

State the formula for the ionic product of water (Kw) for the relationship between pH and pOH and how it is derived.

A

H₂O ⇌ H⁺ + OH-
ionic product of water:
Kw= [H⁺][OH-]
(Ignore H₂O as it doesn’t vary)

31
Q

What is Kw @ 25℃?

A

1x10^-14

32
Q

State the formula of pKw and what it must add up to.

A

pKw = pH + pOH

must always add up to 14

33
Q

What is H₃O⁺?

A

a H⁺ donor and acid

34
Q

What are the values of Ka, [H₃O⁺] and pH with increasing acid strength?

A

High Ka and [H₃O⁺]

low pH

35
Q

What are the values of Kb, [H₃O⁺] and pH with increasing base strength?

A

High Kb and pH

low [H₃O⁺]

36
Q

State what indicators are, how they work and state the general equation for this.

A

indicators = weak acid molecules that change colour with a change of the equilibrium position
HLn ⇌ H⁺ + ln-
acid conjugate base

37
Q

Give an example of an indicators, its colour change and the pH it maintains.

A

phenolphthalein
changes from colourless to pink
from pH range of 0-8.2 to a pH range of 8.2-12

38
Q

Calculate the pH from a [H⁺] of 1 pM.

A

[H⁺] = 1 pM = 1x10^-12 M
= log10(1x10^-12) = -12
= -log10(1x10^-12) = 12
pH = 12 = HIGH

39
Q

Calculate the pH from a [H⁺] of 1 mM.

A

[H⁺] = 1 mM = 1x10^-3 M
= log10(1x10^-3) = -3
= -log10(1x10^-3) = 3
pH = 3 = LOW

40
Q

For a strong acid, what is the starting [Acid] equivalent to?

A

the [H⁺] of the acid

41
Q

What is the equation for calculating the pH of weak acids and how is it derived?

A 
HA ⇌  H⁺ + A-
Ka = [H⁺][A-]/[HA]
Rearrange:
logKa = log ( [H⁺][A-]/[HA])
logKa = log [H⁺] + log ([A-]/[HA])
-pKa = -pH + log ([A-]/[HA])
Into the Henderson-Hasselbach equation:
pH = pKa +log ([A-]/[HA])
42
Q

What is a buffer solution?

A

resists change in pH upon addition of small amounts of either acid or base

43
Q

What is a buffer solution composed of?

A

consists of a solution of a weak acid and the salt of its conjugate base
Or, a weak base and the salt of its conjugate acid
it has a high concentration, as there is an equal amount of each component

44
Q

What pH does a buffer generally maintain?

A

a pH of around the pKa of the acid

45
Q

What happens to this general buffer, if more H⁺ is added?

HA ⇌ H⁺ + A-

A

H⁺ + A- → HA
the conjugate base accepts it, forming the conjugate acid and no pH change occurs
equilibrium position shifts left to resist the change

46
Q

What happens to this general buffer, if OH- is added?

HA ⇌ H⁺ + A-

A

H⁺ + OH- → H₂O
it reacts with H⁺ to form water
equilibrium shifts right
more acid dissocitaes to maintain constant [H⁺]

47
Q

State the buffer system in intrasystemic fluid and what it is used for. (Hint: the system is the same as the blood)

A

use bicarbonate

for metabolic acids

48
Q

State the buffer system in blood and what it is used for.

Hint: what is the alkaline substance that accepts protons ?

A

use bicarbonate and haemoglobin

for metabolic acids and important for carbon dioxide

49
Q

State the buffer system in intracellular fluid.

Hint: what is made in cells?

A

proteins and phoshpates

50
Q

State the buffer system in urine and what it is used for.

A

phosphate and ammonia

for the formation of NH₄⁺

51
Q

State the buffer system in bone and what it is used for.

A

Calcium carbonate and phosphate

for prolonged metabolic acidosis

52
Q

Explain how blood pH is maintained by bicarbonate in plasma using a diagram.

A

see document

53
Q

Define ‘metabolic acidosis/alkalosis.’

A

a build-up of acidic metabolites (e.g. oxalic acid, lactic acid), failure of acid-base elimination in the kidneys

54
Q

Define ‘respiratory acidosis/alkalosis.’

A

too little/too much CO₂ exchanged in lungs

55
Q

Explain how blood pH is maintained by bicarbonate in plasma.

A

H⁺ produced by dissociation of H₂CO₃
protonation reduces affinity of haemoglobin for O₂
O₂ released in peripheral tissues
haemoglobin can also transport CO₂ - also favours oxygen release

56
Q

Draw out the reactions between:

a) histidine and H⁺
b) haemoglobin and CO₂

A

a) Hint: Pentagon with N, NH and double bond below N and opposite (N becomes NH⁺)
b) NH₂ becomes NH=OOH

57
Q

For each of the following names identify the substance involved in the acid/base definitions:

a) Arrhenius
b) Bronstead-Lowry
c) Lewis

A

a) God of water; H⁺/OH- dissolved in ‘water’ or solution
b) Sounds like a philosopher very positive; H⁺ ions
c) Lewis; feeling ‘low’ - ‘electron-pairs’ are negative

Chemistry (12 decks)

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