Topic 8 acids & bases Flashcards
Define a weak acid
Substance that is partially dissociated in water solution
Define a strong acid
Substance that is completely dissociated in water solution
Define a Brønstedt-Lowry acid
A substance that can donate a proton (H+).
Define a Brønstedt-Lowry base
A substance that can accept a proton (H+).
Define a Lewis base
A substance that can donate an electron pair.
Define a Lewis acid
A substance that can accept an electron pair.
Define/explain conjugate base
Species formed when an acid donates a proton (H+) = conjugate base of that acid (so the substance can accept an H+)
3 methods/ways to distinguish betw strong and weak acids (of same concentration) + HOW
- Conductivity. Strong=high cond. since higher concentration of ions (compl diss so lots of H3O+ etc).
- pH. Strong=low (as high conc H3O+)
- Rate of reaction (e.g. w. metal oxides). Strong=fast as higher conc oxonium ions that can react
Required in order for a substance to act as a Brønstedt-Lowry base
lone pair (non-bonding electron pair) to be able to bond H+ (dative covalent)
generally lone pair O or N
3 Strong acids
HCl (hydrochloric acid)
H2SO4 (sulfuric acid)
HNO3 (nitric acid)
Strong bases (examples)
Group 1 hydroxides (e.g. NaOH)
Ba(OH)2
Conjugate acid
The species formed when a base accepts one proton is referred to as the conjugate acid
of the base.
Amphiprotic
Substance that can react AS both acid and base (can gain or lose an H+)
Amphoteric
Substance that can react WITH both acid and base
Properties of acids vs bases
Acids = corrosive, sour taste, form aqueous solutions with pH<7
Bases = corrosive, slippery feel, form aqueous solutions with pH>7
Acid + reactive metal →
→ H2(g) + salt
Acid + metal oxide / metal hydroxide →
→ H2O + salt
Acid + carbonates / hydrogen carbonates →
→ CO2 + H2O + salt
Neutralization
1. definition
2. products
3. exo-/endothermic
- acid + base (reacting completely)
- → H2O + salt generally (if NH3 no water and if … ***check notes-CO2??)
- EXOthermic
Kw expression =
Kw = [H3O+][OH-]
values pKw, pH, pOH for calcs (25degC)
pKw = 14 = pOH + pH
What is pH?
Measure of the concentration of oxonium ions [H3O+]. (logarithmic scale)
How great a change of [H3O+] does this change in pH result in?
1: pH 7→6
2: pH 5→2
3: pH 5→7
pH scale logarithmic ie change 1 pH = tenfold change [H3O+]
1: x10
2: x1000
3: /100
What arrow do you use for
1: weak acid/base dissolved in water
2: strong acid/base dissolved in water
1: ⇌ ie reversible, equilibrium formed, only partially dissociated, reaction not to completion. equilibrium lies on the left (HA, not A-)
2: → reaction goes to completion (completely dissociated in water solution) reaction not reversible
What differs between strong and weak acids?
The extent of dissociation/ionization
“strength” acid & conjugate base
A strong acid is a good proton donor and has a weak conjugate base and vice versa.
“strength” base & conjugate acid
A strong base is a good proton acceptor and has a weak conjugate acid and vice versa.
Difference betw conductivity strong base/acid and weak base/acid
Strong acids and bases of equal concentrations have higher conductivities than weak
acids and bases since they are completely dissociated and their solutions have a higher
concentration of ions.
Strong acid is good/poor proton (H+) donor? & has a strong/weak conjugate base?
Good proton donor
Weak conjugate base
Strong base is good/poor proton (H+) acceptor? & has a strong/weak conjugate acid?
Good proton acceptor
Weak conjugate acid
What is meant by the term ‘acid deposition’?
Acid deposition is the process where acidic particles, gases and precipitates leave the
atmosphere.
Does acid (wet deposition) rain only refer to rain?
No, also includes fog, snow, and dew
What is the pH of “normal rain”? i.e. below what pH is rain considered acid rain?
Normal rain has a pH of 5.6. If the pH of the rainwater is lower
than 5.6 we call it acid rain.
Why is “normal rain” acidic?
All rain is acidic since the carbon dioxide in the atmosphere is dissolved and produces
carbonic acid, H2CO3.
What substances are responsible for acid rain?
nitrogen and sulphur oxides
(the dissolving of these in water that causes the low pH of
the rainwater)
From where are sulfur oxides released? (3 examples)
- naturally from volcanoes
- produced industrially from the burning of sulfur-containing fossil fuels
- from the smelting of sulfur
ores
Give the equations for the reaction of Sulfur to produce Sulfurous and Sulfuric acid.
(Sulfurous = H2SO3, Sulfuric = H2SO4)
S (s) + O2 (g) → SO2 (g)
In the presence of sunlight (UV-light) the sulfur dioxide is converted (oxidized) into
sulfur trioxide:
SO2 (g) + O2 (g) → SO3 (g)
These two oxides can react with water and produce sulphurous and sulphuric acid:
SO2 (g) + H2O (l) → H2SO3 (aq) Sulfurous acid
SO3 (g) + H2O (l) → H2SO4 (aq) Sulfuric acid
From where are nitrogen oxides released? (3 examples)
- naturally in electrical storms
- produced by certain
bacteria. - NO is formed in internal combustion engines and in jet engines.
Give the equations for the reaction of Nitrogen to produce Nitrous and Nitric acid.
(Nitrous = HNO2, Nitric = HNO3)
N2(g) + O2 (g) → 2NO (g)
NO is then converted (oxidized) to NO2 by the oxygen in the air:
NO (g) + O2 (g) → NO2 (g)
NO2 can react with water and produce nitrous and nitric acid:
2NO2 (g) + H2O (l) → HNO3 (aq) + HNO2 (aq)
Give examples of Effects of acid deposition (general area)
Vegetation
Lakes and rivers
Buildings
Human health
How does acid deposition affect vegetation?
When the pH in the soil is lowered, it leaches important nutrients, such as Ca2+, Mg2+
and K+. Decrease in Mg2+ can lead to decrease in chlorophyll, which would lower plants
ability to photosynthesize.
Increasing amount of Al3+ (released from rocks at lower pH) damage the roots of trees
and prevent them taking up enough water and nutrients to survive. This can be seen, as
the trees don’t grow as well, the treetops are thinner and they lose their leaves and
become yellow.
How does acid deposition affect lakes and rivers?
The increased levels of Al3+ can kill fish. Most aquatic life forms are also sensitive to a
change in pH ex) many fish have problems surviving in pH below 6.
Below pH = 4 lakes are effectively dead.
How does acid deposition affect buildings?
Stones, particularly marble and limestone, are eroded by acid rain. Marble and
limestone is made up of calcium carbonate, which reacts easily with acids (since the
carbonate ions are bases).
CaCO3 (s) + H2SO4 (aq) ® CaSO4 (aq) + CO2 (g) + H2O
With sulphuric acid, the calcium carbonate form calcium sulphate that is washed away
with rainwater. This leads to severe corrosion of sculptures and buildings.
There is also the possibility of salts forming within the stone and that can lead to
cracking of the stone.
The acid deposition can also react with metals such as iron and speed up the corrosion
rate. This produces ions and increase conductivity, which leads to increases the rate of
electrochemical corrosion
Fe (s) + H2SO4 (aq) ® FeSO4 (aq) + H2(g)
The acid rain can also remove the protective aluminium oxide layer and cause
aluminium to corrode.
Al2O3 (s) + HNO3 (aq) ® Al(NO3)3 (aq) + H2O (l)
How does acid deposition affect human health?
The acids formed from the nitrogen and sulfur oxides are hazardous to health. They
irritate the mucous membranes and increase the risk of respiratory illnesses, such as
asthma and bronchitis. Since water with low pH leaches out metals, there is a higher risk
of getting poisonous metal ions, such as Pb2+ and Al3+ in the drinking water. High levels
of Aluminium ions in the water have been linked to Alzheimer’s disease.
How can the effects of acid rain be reduced (by reducing emissions)?
Lower the amount of NOx and SOx formed by for example:
- improved engine design
- using catalytic converters
- removing sulphur before and/or after the burning of sulphur-containing fuels.
- Switch to alternative methods of energy (e.g solar and wind power); reduce the
amount of fossil fuels used (e.g by increasing public transport etc) - liming of lakes (reduce the impact, after acid rain, not preventative)
What are the 2 types of methods to reduce SO2 emissions?
Pre-combustion
Post-combustion
Describe pre-combustion method of reducing SO2 emissions
Describe post-combustion method of reducing SO2 emissions
Outline liming of lakes
Liming of lakes – adding CaO or Ca(OH)2 to lakes to neutralise the acidity in the lakes.
This increases the amount of Ca2+ in the lakes and precipitates aluminium ions. This has worked in many, but not all lakes, where it has been tried.
What bond is formed when a Lewis acid reacts w a Lewis base?
a coordinate (dative) covalent bond.
(lone pair from the L base)
Are Brønstedt-Lowry acids Lewis acids?
Yes!!
All Brønstedt-Lowry acids are also Lewis acids. The term Lewis acid is usually only
used for species that are not Brønstedt-Lowry acids. Many Lewis acids don’t contain
hydrogen, ex) AlCl3, BF3, FeBr3 etc.
