Acid Rain

Introduction

Acid rain is a topic of great concern to environmental engineers. It can kill fish by lowering the pH of lakes and rivers. It can harm trees and plants by burning their leaves and depriving them of nutrients. It can also weather away stone buildings and monuments. But why is it more of a problem in some places than others?

To answer this question, let’s first look at how rain becomes acidic. Carbon dioxide, CO₂, is a gas found naturally in the air. When CO₂ dissolves into rain droplets, it produces a weak acid called carbonic acid, H₂CO₃. This makes rain slightly acidic naturally. Rain of pH 5 to 6 is common and does not generally cause any problems. When fossil fuels are burned, however, gases such as sulfur dioxide, SO₂, are released into the air. When sulfur dioxide dissolves into rain droplets, sulfuric acid, H₂SO₄, is formed. This rain can be as acidic as pH 4.

In Part I of this experiment, you will study how rain naturally becomes acidic due to CO₂ in the air. You will monitor the pH of water as you add CO₂ by blowing through a straw. In Part II, you will study the effect of acid rain on the pH of different water types. The pH will be recorded as dilute sulfuric acid is added to several water samples.

Objectives

In this experiment, you will

• Use a computer and an NXT to measure pH.
• Study the effect of dissolved carbon dioxide on the pH of distilled water.
• Study the effect on pH of dissolving dilute sulfuric acid in various waters.
• Learn why some bodies of water are more vulnerable to acid rain than others.