Y13 IB Acid Deposition by Melanie Stell

Write out the objective then add notes and explanations, diagrams too.

mstell — 2018-02-05 06:56:11 UTC

Distinguish between pre-combustion and post-combustion methods to reduce emissions of sulfur oxides.

2018-02-05 08:37:35 UTC

There are two approaches to reduction of Sulfur Dioxide pollution from burning fossil fuels:
- Pre-combustion method: removal of the sulfur from the fossil fuels before combustion.
- Post-combustion: removal of the sulfur dioxide from the emissions produced by the combustion.

How it's done:
Pre- combustion: This is usually carried out using hydrogen gas during the refining process (hydrodesufurisation or hydrotreatment).

The hydrogen gas reacts with the sulfur in the crude oil producing hydrogen sulfide gas that can be separated and lead to sulfur recovery units where it is oxidised to sulfur. This produces vast amounts of sulfur that can be used in the rubber industry or simply stored.

Post-combustion: The gases formed by combustion of fossil fuels is passed through alkaline 'scrubbers' that remove any acidic gases. These scrubbers contain calcium oxide, formed by roasting calcium carbonate, and water spray that combines with the sulfur dioxide making calcium sulfite dihydrate, CaSO₃.2H₂O.

CaO + SO₂ --> CaSO₃

Removing SO₂ from the gases prevents its conversion to acid rain. Scrubbing systems are now commonly used to minimize the environmental effects of large-scale fossil fuel combustion.

State the sources of the oxides of sulphur and nitrogen together with the effects of acid deposition

2018-02-05 08:38:54 UTC

The primary emissions responsible for acid deposition are sulphur dioxide and oxides of nitrogen from the combustion of coal, oil and natural gas. Nitrogen monoxide produced from internal combustion engines where heat forces nitrogen and oxygen to combine.
N2 + O2 --> 2NO
The combustion of these compounds are transformed into sulphuric and nitric acid.

Effect of acid deposition:

Impact on plants: Causes important minerals to get washed away (Mg, Ca, K ions). This is known as leaching.
They can block pores for gas exchange.
Toxic substances damage the roots and leaves.

Impact on water: Fish cannot survive below a pH of 5 so they die.
Eutrophication: oxygen depletion and prevents light from entering

Impact on human health: Irritation to the eyes, respiratory tract problems that can increase the risk of asthma or emphysema.

State the effects of acid deposition on plant life, water system and buildings

2018-02-05 08:41:36 UTC

Effect on vegetation: The acid (H+) can displace metal ions from the soil that are washed away. Ions such as Magnesium are needed for the plant to grow, aluminium lions are also dissolved from rocks and taken in by plants and limits water uptake.

Lakes and rivers: Aquatic life is sensitive to pH. Acid rain can dissociate hazardous ions form rocks (such as Al 3+) that can alter the pH of the water and damage aquatic life.

Buildings:limestone and marble are erodqdby acid rain and dissolve away exposing a fresh surface to react with acid.

CaCO3 + H2SO4----> CaSO4 + H2O+CO2

acid deposition occurs when oxides of nitrogen or sulfur dissolve in water to form nitric acid, HNO3, nitrous acid, HNO2, sulfuric acid, H2SO4 and solfurous acid, H2SO3.

2018-02-05 08:42:10 UTC

forming of oxides (combustion):
S(s) + O₂(g) ——> SO₂(g)

2S(s) + 3O₂(g) ——> 2SO₃(g)
2SO₂(g) + O₂(g) <——> 2SO₃(g)

N₂ + O₂---> 2NO

2NO + O₂----> 2NO₂

Forming of acids:

SO₂(g) + H₂O(g) ——> H₂SO₃(g) [sulfurous acid]

SO₃(g) + H₂O(g) ——> H₂SO₄(g) [sulfuric acid]

H₂O + 2NO₂---->HNO₂ + HNO₃[nitrous acid and nitric acid respectively]

2HNO₂ + O₂------>2HNO₃

Rain contains dissolved CO2 so it is naturally acidic with a pH of 5.6. The pH of acid deposition is below 5.6.

2018-02-05 08:48:07 UTC

CO2(g) + H2O(l) -> H2CO3(aq)
H2CO3(aq) -> HCO3-(aq) + H+(aq)
HCO3-(aq) -> CO3.2-(aq) + H+(aq)

The H+ ions decrease the pH of water (makes it more acidic)
= pH 5.6

Equations for the reactions of acids in acid deposition with reactive metals and carbonates

2018-02-05 08:51:27 UTC

HCl(aq) + Mg(s) ----->
MgCl2(aq) + H2(g)

HCl(aq) + CaCO3(s) ------>
CaCl2(aq) + H2O(l) + CO2(g)