2.94- Atmospheric pollution

What is acid rain

Rainwater that is more acidic than normal

Why is normal rainwater slightly acidic

Because carbon dioxide dissolves in it, forming weak carbonic acid (H₂CO₃).

What is the pH of normal rainwater

5.6

What is the pH of acid rain and why is it lower

Acid rain has a lower pH (around 2.0 – 5.4) because it contains stronger acids

• Sulfuric acid (H₂SO₄)

• Nitric acid (HNO₃)

What do these acids come from

Sulfuric acid → sulfur dioxide

Nitric acid → NO_x compounds

How is sulfur dioxide produced

by the combustion/oxidation of sulfur with oxygen

What processes cause the combustion/oxidation of sulfur with oxygen, producing SO₂

• Volcanoes

• Industrial processes

• Motor vehicles

Name 4 properties about sulfur dioxide

• Colourless gas

• Has an irritating smell

• Poisonous

• Though to be one of the main causes for bronchitis and lung cancer

Explain how sulfuric acid is produced from sulfur dioxide

1. Sulfur dioxide mixes with the water in the atmosphere, forming sulfurous acid (H₂SO₃) - weal acid

2. Sulfurous acid then reacts with the oxygen in the air and forms sulfuric acid which is much stronger

Give the word and chemical equation for: Sulfur dioxide mixes with the water in the atmosphere, forming sulfurous acid (H₂SO₃)

sulfur dioxide + water → sulfurous acid
SO₂ + H₂O → H₂SO₃

Give the word and chemical equation for: Sulfurous acid then reacts with the oxygen in the air and forms sulfuric acid which is much stronger

sulfurous acid + oxygen → sulfuric acid
2H₂SO₃ + O₂ → 2H₂SO₄

Summarize the whole process of sulfur dioxide forming sulfuric acid - word + chemical equation

sulfur dioxide + water + oxygen → sulfuric acid
2SO₂ + 2H₂O + O₂ → 2H₂SO₄

Explain the two ways nitrogen monoxide (NO_X) compound is formed

Nitrogen monoxide (NO) is formed as an indirect result of the burning of fossil fuels since this combustion process creates high temperatures which cause nitrogen and oxygen from the air to react.

N₂ + O₂ → 2NO

Nitrogen monoxide can also be produced naturally during thunderstorms (electrical discharge)

Is nitrogen monoxide a dangerous gas

No

Explain what happens when nitrogen monoxide comes in contact with oxygen from the air

it forms nitrogen dioxide (NO₂)

What are 3 properties of nitrogen dioxide

• Dense, brown gas

• Highly toxic

• Irritates the breathing passages

Give the equation for how nitrogen monoxide produces nitrogen dioxide

2 NO + O₂ → 2 NO₂

Explain how nitrogen dioxide produces nitric acid

Nitrogen dioxide is acidic and reacts with water and oxygen in the air to form nitrous acid and nitric acid: this produces acid rain

• NO₂ + H₂O → HNO₂ + HNO₃

 

HNO₂ (nitrous acid) reacts with more oxygen to form HNO₃ (nitric acid) - all nitrogen dioxide ends up becoming nitric acid

• 2 HNO₂ + O₂ → 2 HNO₃
  
  

Summarize the process of nitrogen dioxide reacting with water and oxygen in the air to produce nitric acid

nitrogen dioxide + oxygen → water + nitric acid
4NO₂ + 2H₂O + O₂ → 4HNO₃

Explain the effects of acid rain on the land

• Acid rain falls into soil.

• At first, nitrates (from nitric acid) help plants grow.

• But acid rain reacts with soil minerals into soluble salts.

• These salts leach (wash) away (soluble) into deeper soil where plant roots can’t reach so soil loses nutrients.

• One harmful salt, aluminium sulfate, damages tree roots.

• Damaged roots make trees weaker and sick, often dying from lack of nutrients and disease.

Explain the effects of acid rain in water

• Acid rainwater flows through soil into lakes and rivers.

• Lakes are more affected — they become more and more acidic which causes fish to die because the water is too acidic, and aluminium builds up on their gills, clogging them.
  • Acid lakes look crystal clear — but that’s bad, because it means no life (no fish, insects, or plants).
  

Explain the effects of acid rain on buildings

• Acid rain corrodes metals and damages buildings made of limestone or marble by wearing them down faster.

What can be done to reduce acid rain

• Reduce SO₂ emissions

• Reduce NO_x emissions

How to reduce sulfur dioxide emissions

a. Power stations can reduce sulfur dioxide levels by filtering it out with limestone to form calcium sulfate

b. Lower sulfur fuels can be produced and used instead

How can nitrogen oxide emissions be reduced

a. Catalytic converters can be fitted on petroleum engines, reacting nitrogen monoxide with carbon monoxide which forms the non-toxic gases nitrogen and carbon dioxide

2NO + 2CO → N₂ + 2CO₂