Water
Applying Water
Waterglossary term (opens in a new window) has many useful applications. Farmers depend on water for watering crops, but the importance of water goes even beyond that. As one might expect, freezing temperatures can be devastating to warm-weather crops, such as oranges and lemons. If an orange crop were to freeze during a cold night, a farmer could lose a great deal of fruit. Fortunately, water can come to the rescue.
Farmers of citrus crops closely watch weather forecasts. If freezing temperatures are predicted overnight, farmers may initiate a water-spraying strategy to cover their fruit trees. The trees and fruit are coated in a continuous spray of water. The water freezes under certain conditions when air temperature is 0°C (32°F) or lower. A protective layer of ice forms around the plants. Coated by the ice, the plants are prevented from dipping below freezing temperatures. The layer of ice also prevents wind from further stripping heat energyglossary term (opens in a new window) from the plants.
When covered in ice, plants are teetering just above the freezing point. If the liquidglossary term (opens in a new window) inside the plants were pure water, the plants would be in danger of freezing at 0°C. However, since the water inside plants contains various molecules, nutrients, and other solutes, its freezing temperature is slightly lower than 0°C. As a result, plants coated in a continuous layer of ice are protected from freezing.
STEM and Water
Clearly, water is vital to life on Earth. Unfortunately, waste and pollution from human activity has contaminated Earth’s oceans, lakes, and rivers.
The burning of fossil fuels has increased dramatically since the industrial revolution of the 19th century. Burning oil, coal, and natural gas powers most of our energy needs. However, this process releases many harmful gases—including carbon dioxide, sulfur dioxide, and nitrogen oxides—which react with water vapor in the atmosphere. The products of such reactions include sulfuric acid, nitric acid, and carbonic acid.
Acidic water vapor falls to Earth as rain, snow, fog, or other precipitation. This phenomenon is referred to as acid rain, which applies to rain below a normal pH of approximately 5.6. Scientists can accurately measure the acidity of rain using a pH meter. Acid rain contaminates bodies of water and is detrimental to wildlife. Land animals, insects, fish, and other organisms are all harmed and killed by acidic lakes and rivers.
A great deal of scientific research has been conducted to determine the causes and impacts of acid rain. During this time, the government has passed numerous laws in an effort to reduce the burning of fossil fuels. Limits have been imposed on the amount of carbon and sulfur emissions that factories can produce. Marine biologists are particularly concerned about how the increased concentration of carbon dioxide in the atmosphere is acidifying the oceans. Many ocean-dwelling organisms are very sensitive to changes in acidity. Organisms that make shells or skeletons out of calcium carbonate are seriously impacted by ocean acidification. For example, corals cannot make the skeletons that are the basis of coral reefs.
Today, many scientists and bioengineers are researching alternative energy sources that will reduce our dependence on fossil fuels, thus reducing the amount of acid rain that falls to Earth. Alternative energy sources include wind, solar, and geothermal energy.
Analyzing Effects of Acid Rain
Teacher Note
This summative assessment is intended to stimulate student learning about acid rain and applying technological designs to measure the acidity of water. Teachers may implement the activity in think-pair-shares or small groups.
Read the article “Surviving Acid Rain” and then respond to the two prompts below.
