The boiling point of water is the temperature at which liquid water transitions into a gaseous state, or vapor. Under specific, controlled conditions, pure water boils at exactly 212 degrees Fahrenheit (°F). This phase change occurs when water molecules gain enough energy to overcome the surrounding atmospheric pressure, allowing vapor bubbles to form. This standard measurement is the baseline for scientific applications and everyday kitchen tasks.
The Standard Boiling Point in Fahrenheit
The precise temperature of 212°F is the established boiling point for pure water only when measured at Standard Atmospheric Pressure. This pressure is typically observed at sea level, where the weight of the air column above is at its greatest.
Daniel Gabriel Fahrenheit, who developed the scale in the early 18th century, established the freezing point of water at 32°F and its boiling point at 212°F. This creates a span of 180 equal degrees between the two primary physical states of water. This specific 212°F temperature is used in most textbooks and general reference materials.
Factors That Change the Boiling Point
The 212°F measurement is not universal, as two main factors can significantly alter the temperature at which water boils. The first is the surrounding atmospheric pressure, which is directly related to altitude. As elevation increases, the atmospheric pressure pushing down on the water decreases, meaning the water molecules require less energy to escape as vapor.
This inverse relationship causes water to boil at a lower temperature in high-altitude locations. For example, at 5,000 feet above sea level, the boiling point drops to approximately 203°F, and at 10,000 feet, it falls to about 194°F. This lower temperature means that foods cooked by boiling take longer to prepare, often requiring adjustments to recipes.
The second factor involves adding impurities, or dissolved solids, to the water. Substances like salt or sugar, known as non-volatile solutes, interfere with the water molecules’ ability to transition into vapor. This phenomenon is called boiling point elevation. The introduction of these particles means more energy is needed to overcome the intermolecular forces in the solution.
Adding salt to cooking water raises the boiling temperature slightly, typically by only a few degrees Fahrenheit in culinary applications. For instance, a solution with 29.2 grams of salt dissolved in one kilogram of water raises the boiling point by about 0.9°F. This small increase in temperature can be beneficial for cooking, as it allows the food to be exposed to slightly higher heat.
Comparing Fahrenheit and Celsius
While the Fahrenheit scale sets the boiling point at 212°F, the internationally used Celsius scale uses a simpler figure. At standard atmospheric pressure, 212°F is precisely equivalent to 100 degrees Celsius (°C). The Celsius scale was defined by setting the freezing point of water at 0°C and the boiling point at 100°C.
The Celsius scale uses 100 divisions for this temperature range, whereas the Fahrenheit scale uses 180 divisions. This difference means that one degree Celsius represents a larger temperature interval than one degree Fahrenheit. To convert from Fahrenheit to Celsius, subtract 32 from the Fahrenheit temperature and then multiply the result by five-ninths.