IB chemistry: topic 8: Bronsted-Lowry Acids and Bases / acid deposition

what is a Bronsted-Lowry acid?

species that gives away a proton (H+)

what is a Bronsted-Lowry base?

species that accepts a proton (H+) using its lone pair of electrons

what is a conjugate acid base pair?

two species that are different from each other by a H+ ion

what are amphiprotic species?

species that can act both as proton donors and acceptors

what are examples of amphiprotic species?

water

amphiprotic vs ampthoteric

ampthoteric - more general, species act as acids and bases.

ampthiprotic - more specific, species accept/donate H+ ions.

what does amphoteric mean?

species that can act as both acid and base - general term

acid + metal

salt + hydrogen

what are signs of a more reactive reaction?

• more effervescence

• the metal dissolves faster

• more exothermic

acid + metal oxide

salt + water

acid + metal hydroxide

salt + water

acid + metal carbonate

salt + water + carbon dioxide

acid + metal hydrogencarbonate

salt + water + carbon dioxide

what is a neutralisation reaction?

an acid (pH <7) and a base/alkali (pH >7) react together to form water (pH = 7) and a salt

what are spectator ions in neutralisation reactions?

ions which are not involved in the formation of water - form salts

how is carbonic acid formed?

CO2 dissolved in water

H2O (l) + CO2 (g) ⇌ H2CO3 (aq)

what is carbonic acid?

a weak acid and dissociates in the following equilibrium reaction giving a pH of 5.6

H2CO3 (aq) ⇌ H+ (aq) + HCO3- (aq)

what pH is acid rain?

pH of below 5.6

what is wet deposition?

wet acid deposition refers to rain, snow, sleet, hail, fog, mist and dew

what is dry deposition?

dry acid deposition refers to acidic particles and gases that fall to the ground as dust and smoke

how is acid deposition formed?

acid deposition is formed when nitrogen or sulfur oxides dissolve in water to form HNO3, HNO2, H2SO4 and H2SO3

what reactions form sulfur based acids?

Fossil fuels are often contaminated with small amounts of sulfur impurities.

When these contaminated fossil fuels are combusted, the sulfur in the fuels get oxidised to sulfur dioxide.

what reactions form nitrogen based acids?

high temperatures in internal combustion engine

describe the formation of sulfur-based acids/acid rain? EQUATIONS

S (s) + O2 (g) → SO2 (g)

2SO2 (g) + O2 (g) ⇌ 2SO3 (g)

SO2(g) + H2O (l) → H2SO3 (aq)

SO3 (g) + H2O (l) → H2SO4 (aq)

describe the formation of nitrogen-based acids/acid rain? EQUATIONS

N2 (g)+ O2 (g) ⇌ 2NO (g)

2NO (g) + O2 (g) ⇌ 2NO2 (g)

2NO2 (g) + H2O (l) → HNO2 (aq) + HNO3 (aq)

4NO2 (g) + 2H2O (l) + O2 (g)→ 4HNO3 (aq)

describe the formation of sulfur-based acids/acid rain?

contaminated fossil fuels are combusted, the sulfur in the fuels get oxidised to sulfur dioxide,

further oxidation to sulfur trioxide,

sulfur dioxide and sulfur trioxide then dissolve in rainwater droplets to form sulfurous acid and sulfuric acid.

LIGHTNING STRIKES

describe the formation of nitrogen-based acids/acid rain?

nitrogen and oxygen combine to form nitrogen monoxide,

nitrogen monoxide reacts further forming nitrogen dioxide,

nitrogen dioxide gas reacts with rain water to form a mixture of nitrous and nitric acids, which contribute to acid rain,

how does lightning strikes create nitrogen-based acid rain?

lightning strikes trigger the formation of nitrogen monoxide/dioxides.

nitrogen dioxide gas reacts with rain water and more oxygen to form nitric acid.

what is limestone/marble made of?

calcium carbonate

what are the effects of acid rain on buildings/bridges?

buildings begin to crumble,

metal bridges corrode and rust

what are the effects of acid rain on plants?

acid particulates can block stomata ( plant pores) and prevent gaseous exchange

what are the effects of acid rain on water?

pH levels drop too low and life cannot be maintained

what is eutrophication?

excessive algal growth that results in oxygen depletion and stagnation of waterways

what causes eutrophication?

Nitrate ions from nitric acid in acid rain can contibute to over-fertilization of waterways and lead to eutrophication

what are the effects of acid rain on humans?

increase the risk of respiratory diseases such as bronchitis, asthma and emphysema,

if in contact with metal pipes, increased risk that toxic metal ions will be released into the water supply

what are ways that sulfur oxide can be removed from fossil fuels?

can be removed either pre or post combustion

how is sulfur naturally prduced?

volcanic eruptions

how does precombustion remove sulfur from fossil fuels?

sulfur is removed by reacting it with hydrogen in a process called hydrodesulfurization

how does postcombustion remove sulfur from fossil fuels?

waste gases are passed through a wet slurry of calcium oxide and calcium carbonate which react with the SO2 and produce calcium sulfate