How does acid rain form?
Burning coal and diesel fuel releases SO2 and NO2 gases into the air. Wind carries them far away, and in clouds they react with water and oxygen to form acids.
- SO2 + H2O → H2SO3: this forms sulfurous acid. It oxidizes further to sulfuric acid.
- 4NO2 + O2 + 2H2O → 4HNO3: this forms nitric acid.
Why is clean rain not pH 7?
CO2 from the air dissolves in rainwater and forms weak carbonic acid: CO2 + H2O → H2CO3. So the pH of clean rain is not 7 but about 5.6. Rain with a lower pH is called acid rain.
When the pH falls by one, the hydrogen ion concentration becomes 10 times greater. So the pH 3.5 rain at the start of the simulator is more than 100 times more acidic than clean rain at pH 5.6.
What does acid rain harm?
- It washes calcium and magnesium out of the soil, and plants dry out.
- It dissolves aluminum from the soil and carries it into rivers and lakes. In water at about pH 5, most fish eggs do not hatch.
- It dissolves and damages limestone and marble: CaCO3 + H2SO4 → CaSO4 + H2O + CO2↑.
Explore the acid rain cycle in the Nalukh chem app
Match each source with its solution and raise the pH of the rain. This simulator is included with full access. The app is free to download, and 2 units and 5 simulators are open with no sign-up.
How do you use the simulator?
- Grab a source card from the tray in the middle of the cycle on the left.
- Drag it to one of the four solutions on the right. If it does not match, the slot shakes and a hint appears on the tray.
- When you place it correctly, the pH rises on the Acid in rain meter in the top corner. The explanation card tells you why that pair works.
- Watch the cycle: smoke, wind, rain, evaporation. As the air gets cleaner, there are fewer raindrops, and plants go from dried out to sprouting and then to flowering.
- When you solve all four, the rain reaches pH 5.6 and the card shows the reaction of clean rain.
The four pairs are as follows.
| Source | Solution | Why |
|---|---|---|
| Factory | Sulfur scrubber | Washes the smokestack gas and captures SO2 |
| Coal stove | Low-sulfur coal | Releases little SO2 when it burns |
| Old car | Catalyst | Converts NO2 into harmless N2 |
| Diesel generator | Wind turbine | Generates electricity without burning fuel |
Tasks to try in the simulator
- Write down the pH each time you solve a source. The value rises: 3.5, 4.0, 4.6, 5.1, 5.6.
- Find out how many sources you must solve before the plants sprout. Answer: two.
- Calculate how many times greater the hydrogen ion concentration is at pH 3.5 than at pH 5.1. Answer: about 40 times.
- Drag the Old car card to Sulfur scrubber and read the hint. Think about which gas is the main one in car exhaust.
