8.5 Acid Deposition

Acid Rain: Meaning, causes, problems and solutions

British students are likely to have studied this topic.

However, they will need to be able to write equations to explain what they know.

All rain is acidic due to dissolving CO₂ and forming the weak Carbonic acid H₂CO₃

Write the Chemical Equation for the formation of Carbonic Acid:

____________ (l) + ____________(g) ⇌ _________________(aq)

Write two equations demonstrating Carbonic Acid forming H⁺ ions.

1_______________________________________________________________

2_______________________________________________________________

Note:

Normal Rain will not have a pH lower than 5.6

Fossil Fuels naturally contain small amounts of Sulphur.

This will burn to form Sulphur Dioxide, (SO₂)

• Write the Chemical equation for this combustion

Sulphur Dioxide slowly reacts with Oxygen to make Sulphur Trioxide, (SO₃)

• Write the Chemical equation for this reaction

Sulphur Trioxide dissolves in water to form Sulphuric Acid

• Write the Chemical equation for this reaction

Fossil Fuels need Oxygen to burn. But air also contains Nitrogen. These two gases don’t usually react because the Activation Energy is very high.

• What is it about the bonding in Nitrogen (N₂) that makes the Activation Energy so high?

But engines are very hot so Nitrogen and Oxygen combine to make Nitrogen Monoxide, (NO)

• Write the Chemical equation for this reaction

Nitrogen Monoxide slowly reacts with Oxygen to make Nitrogen Dioxide, (NO₂)

• Write the Chemical equation for this reaction

Nitrogen Dioxide dissolves in water to form Nitric Acid & Nitrous Acid (HNO₂)

• Write the Chemical equation for this reaction

Nitrous Acid (HNO₂) also slowly reacts with Oxygen to form Nitric Acid

• Write the Chemical equation for this reaction

It’s possible to remove Sulphur from Petrol and diesel before they are burned.

This is the pre-combustion method about which we don’t seem to need to know anything!

Post-combustion methods involve dealing with the acidic oxides made during combustion before they get into the atmosphere.

1 - Catalytic converters. It’s not that difficult to remove Sulphur from liquid fuels like petrol and diesel. So the difficulty is the Nitrogen Oxides that are produced by combustion. Catalytic converters are found in exhaust pipes and speed up the reaction between Nitrogen Monoxide (NO) with Carbon Monoxide (CO) to form Nitrogen and Carbon Dioxide. GCSE students learn that they contain precious metals like Platinum, Palladium and Rhodium

• Write the Chemical equation for this reaction

2 – Coal-fired Power Stations – it’s very difficult to remove Sulphur from solid fuels. So we neutralise the Sulphur Oxides made when they are burned by dropping powder Calcium Oxide (Lime) down the chimney.

• Write the Chemical equation for this reaction