Acids and Bases Flashcards
1
Q
define a bronsted-lowry acid
A
it is a proton donator/H+ donor
2
Q
define a bronsted-lowry base
A
it is a proton acceptor/H+ acceptor
3
Q
define a amphiprotic species
A
it is a species that is able to both donate and accept a proton, and thus able to react both as an acid and a base
4
Q
define a amphoteric species
A
a species that can act as both acid and base
5
Q
what is a dative bond
A
where both the valence electrons from a molecule is donated to the bond
6
Q
is H+ the same as H3O+
A
yes
7
Q
HCl + NH3 ––> NH4+ + Cl-
what is the acid and the conjugate base?
A
HCl = acid
Cl- = conjugate base
8
Q
acid + base ––>
A
salt + water (H20)
9
Q
what are alkalis?
A
- substances which form OH- ions in solution when they dissolve
- soluble bases
- all alkalis are bronsted-lowry bases
- but not all bronsted-lowry bases are alkalis
10
Q
what colour is litmus in acid
A
red
11
Q
what colour is litmus in base
A
blue
12
Q
what colour is methyl orange in acid
A
red
13
Q
what colour is methyl orange in base
A
yellow
14
Q
what colour is phenolphthalein in acid
A
colourless
15
Q
what colour is phenolphthalein in base
A
pink
16
Q
acid + metal ––>
A
salt + hydrogen
17
Q
acid + carbonate ––>
A
salt + water + carbon dioxide (CO2)
18
Q
acid + metal oxide (base) ––>
A
salt + water (H2O) (ionic, made up of ions)
19
Q
equation for pH
A
pH = –log [H3O+]
or
pH = –log [H+]
20
Q
what units does pH have
A
none
21
Q
[H+] =
A
10^(–pH)
22
Q
what does a one unit change in the pH mean
A
there has been a 10-fold change in [H+]
23
Q
what does a change from pH 7 to pH 11 mean in terms of [H+]?
A
40x decrease in [H+]
24
Q
[H3O+]*[OH–] =
A
Kw
25
what is [H+] best written as?
[H3O+]
26
what is the pH a measure of
the concentration of [H+]
27
what happens at pH 7 (in terms of the concentration of [H30+] and [OH–])
there is equal amounts of [H3O+] and [OH–], it is neutral
28
in acids, there are _____ [H+] ions than [OH-]
more
29
in bases, there are _____ [H+] ions than [OH-]
less
30
when neutral, [H3O+] ____ [OH–]
equals
31
Kw =
10^(–14) = [H3O+]*[OH–] at (25ºC)
32
what are the units for concentration
moldm^(-3)
33
what concentration is considered a concentrated acid?
anything above 1moldm^(-3)
>1moldm^(-3)
34
what is the definition of a concentrated acid
an acid that doesn't have acid like properties
ie. it doesn't turn litmus paper red, do not release hydrogen gas from metals, do not release carbon dioxide from carbonates etc.
35
what does the size of Kw tell us about the ionisation of a compound/molecule?
- a small value represents that the reaction has mostly reactants
- a large value represents that the reaction is mostly products
- therefore there is are ions when Kw is larger vice versa
36
what is Kw?
it is the ionic product of water
37
pH+pOH =
14
38
what is the definition of a dilute acid
an acid that is in water and has dissociated into H3O+ ions to give acid like properties
H3O+ is:
- what turns litmus red
- releases CO2 form carbonates
- makes excellent electrical conductors
39
definition of strong acids
strong acids ionise completely in solution
they transfer all of their protons to water
(H2O + H+ ––> H3O+)
40
what size is the equilibrium constant when acids are strong? and what does it tell you about the position of the equilibrium?
large and the equilibrium lies to the right
41
definition of weak acids
- weak acids will transfer a few protons to water
- only a small portion of acid will turn into ions, most will remain as molecules
42
what do weak acids have?
carbon
43
how do you identify a weak acid?
carbon is present in the acid
44
what size is the equilibrium constant when acids are weak? and what does it tell you about the position of the equilibrium?
the equilibrium constant is small and it lies to the left because it is mostly reactants
45
how do you write a Ka expression for
CH3COOH + H2O ––> CH3COO– + H3O+
Ka= products / reactants
= [CH3COO–] [H3O+] / [CH3COOH]
you do not include liquids in K expressions
46
definition of weak base
- it doesn't ionise fully
- it only ionises partially
- equilibrium lies to the left
- Kb value is low/small
47
definition of strong base
- it ionises fully
- equilibrium lies to the right
- Kb value is high/large
48
strong acids and bases do what?
they completely dissociate/ionise in water
49
weak acids and bases do what?
they only partially dissociate/ionise in water
50
10molL^-1 HCl = a _________ of a __________ acid
fill in the gaps
- concentrated solution
- strong
51
what is acid deposition
how to put acid in an environment
52
what are some causes of acid deposition
- wet acid deposition
- rain
- snow
- sleet
- hail
- fog
- mist
- dew
all fall to the ground as aqueous precipitates
- dry acid deposition
- acidifying particles
- gases fall to ground as dust, smoke
these later dissolve in water to form acids
53
what is the pH of normal rain
5.6 (rain is naturally acidic)
54
what counts as acid rain?
any rain that has pH below 5.6 (normal rain)
55
what are the primary pollutants to acid rain
oxides of sulphur and nitrogen
56
is acid rain a primary or secondary pollutant
secondary as it is produced when acidic gases (oxides of sulphur and nitrogen) are dissolved in water
57
how is sulfur dioxide produced
burning fossil fuels
produces H2SO3 or H2SO4 when dissolved in water, which are strong acids
58
how is nitrogen oxides produced
internal combustion engines
produces HNO3 and HNO2 when dissolved in water which are strong acids
59
what are the effects on acid deposition
- impact on materials
- impact on plant life
- impact on water
- impact on human health
60
how can we reduce SO2 emissions
pre-combustion methods:
- remove the sulfur present in coal or oil before combustion
- hydrodesulfuristion, catalytic process which removes sulphur from refined petroleum products by reacting it with hydrogen to for hydrogen sulphide: H2S
post-combustion methods:
- flue-gas desulfurisation, removes up to 90% of SO2 from flue gas before it is released into the atmosphere. uses wet slurry of CaO and CaCO3 which reacts with SO2 to form neutral product: CaSO4
61
how can we reduce emissions that cause acid rain in general?
lower the demand for fossil fuels: use more efficient energy transfer systems, public transport, and switching to renewable energy sources are all ways of reducing emissions
62
how can we reduce NOx emissions
- catalytic convertor in vehicles, catalyst converts toxic emissions into relatively harmless products
- lower temperature combustion, the formation of nitrogen monoxide is reduced at lower temperature
63
what is a lewis acid
an electron pair acceptor (electrophile, electron-deficient)
64
what is a lewis base
an electron pair donator (nucleophile, electron-rich)
65
what is a dative covalent bond
where one atom donates both electrons to the bond
66
what bonds are lewis acid-base reactions
covalent, which will always be dative
67
are all bronsted-lowry acids lewis acids or are all lewis acids bronsted-lowry acids
all bronsted-lowry acids lewis acids but not all lewis acids are bronsted-lowry acids
68
pH =
– log [H30+]
69
[H3O+] =
10^-Ph
70
pOH =
– log [OH–]
71
[OH–] =
10^-pOH
72
pH + pOH =
14
73
pH + pOH =
pKw
74
Kw = in terms of [H3O+] and [OH–]
[H3O+] [OH–] = 10^ (–14)
75
Kw = in terms of Ka and Kb
Ka x Kb
76
pKw = in terms of pH and pOH
pH + pOH = 14
77
pKw = in terms of pKa and pKb
pKa + pKb
78
do you include liquids in K expressions
nonononono
79
the stronger the acid, the ________ the pKa value
lower
they are inversely propotional
80
what assumptions are you making when calculating the pH of weak acids
eg. ants contain formic acid (HCOOH). At concentration of 0.01mol L^(-1), what is the pH of squashed ant? pKa = 3.75
[HCOO–] = [H3O+]
- ignore [H3O+] from water because this is negligible
[HCOOH] = 0.01 mol L^(–1)
- because hardly any of the HCOOH has reacted
81
for weak acids, what does [H3O+] =
...___________
√ [acid/HA] x Ka
82
what assumptions are you making when calculating the pH of weak acids
eg. the ammonia you wash windows with has a concentration of 0.1mol L^(–1). What is its pH? pKa(ammonium ion) = 9.24
[NH4+] = [OH–]
- ignore [OH–] from water because this is negligible
[NH3] = 0.1mol L^(–1)
- because hardly any of the NH3 has reacted
83
what is the conjugate base of H2CO3
HCO3–
84
what is the conjugate acid of HSO4–
H2SO4
85
the stronger the acid (___ pKa), the weaker the conjugate base (____ pKb)
low pKa
high pKb
86
the weaker the acid (____pKa), the stronger the conjugate base (___pKb)
high pKa
low pKb
87
the stronger the base (____pKb ), the weaker the conjugate acid (___pKa)
high pKb
low pKa
88
the weaker the base (____pKb), the stronger the conjugate acid (____pKa)
low pKb
high pKa
89
what is the relationship between Ka and pKa
inverse, so high Ka means low pKa vice versa
90
what is the relationship between Kb and pKb
inverse, so high Kb means low pKb vice versa
91
what is the definition of a buffer
an aqueous solution consisting of a weak acid and its conjugate base (or a weak base and its conjugate acid) that resists changes to pH when small amounts of acid or base are added
92
how do you make a buffer solution
1. mixing roughly equal amounts of a weak acid and its conjugate base
or
2. partially neutralising a weak acid with a strong base, so that some of the weak acid remains and the rest has been converted to its conjugate base
93
Strong acids produce n_______ a______
neutral anions
this refers to the ability of the species to react further
eg: HCl ––> Cl– + H+
=> will not react further
94
strong bases produce n________ c_______
neutral cations
this refers to the ability of the species to react further
eg: NaOH ––> OH– + Na+
=> will not react further
95
how do buffers keep the pH constant?
they react away any extra acid or base that is added to the solution by reacting them with a strong acid/base conjugate.
they are in an equilibrium reaction so it works according to Le Chatelier's principle
96
when does the equivalence point happen
when n(acid)=n(base)
on graph:
half-way up the point of inflection
97
Why does the point of inflection happen
in most titrations, it is found that a big jump in pH occurs at the point of inflection
98
Study the graphs in your booklet, pg 47
99
what are indicators
they are very weak acids that have a different colour to their conjugate bases
100
where is the buffer region in a graph
the flattish region of the titration curve (where the pH is hardly changing)
101
at half way to the equivalence point, pH=
pH=pKa(weak acid)
102
where does the equivalence point occur for a:
strong acid weak base
pH=7
103
where does the equivalence point occur for a:
strong acid weak base
pH<7
104
where does the equivalence point occur for a:
weak acid strong base
pH>7
105
where does the equivalence point occur for a:
weak acid weak base
pH=7
106
what is hydrolysis
it is a proton transfer
how to remember:
[H+] is also known as proton
107
for every titration, there are at least two steps: Neutralisation and hydrolysis; explain these two steps
1. neutralisation: eg.
acid + base ––> salt + water
- exist as ions in solution and will either do hydrolysis
2. hydrolysis:
proton transfer
