On the Fahrenheit temperature scale, at what temperature does pure water freeze under standard atmospheric pressure?

Introduction / Context:

Different temperature scales are used in science and everyday life, such as Celsius, Fahrenheit and Kelvin. Knowing the key fixed points on these scales, like the freezing and boiling points of water, is important for conversions and basic understanding of thermometry. This question asks for the freezing point of pure water on the Fahrenheit scale under standard atmospheric conditions.

Given Data / Assumptions:

• We consider pure water in equilibrium between solid and liquid phases.
• The pressure is one atmosphere (standard atmospheric pressure).
• The Fahrenheit scale is used, not Celsius or Kelvin.

Concept / Approach:

On the Celsius scale, pure water freezes at 0 °C and boils at 100 °C under one atmosphere. On the Fahrenheit scale, these two fixed points are 32 °F for freezing and 212 °F for boiling. The interval between 32 °F and 212 °F is divided into 180 equal parts, making the Fahrenheit degree smaller than the Celsius degree. Therefore, the freezing point of water corresponds to 32 °F on this scale.

Step-by-Step Solution:

Verification / Alternative check:

Temperature conversion formulas between Celsius and Fahrenheit are given by F = (9 / 5) * C + 32. Substituting C = 0 °C (freezing point on Celsius) gives F = (9 / 5) * 0 + 32 = 32 °F. This confirms that water freezes at 32 °F. Substituting C = 100 °C gives F = (9 / 5) * 100 + 32 = 212 °F, matching the boiling point on Fahrenheit scale.

Why Other Options Are Wrong:

Option B: 0 °F is a colder temperature on this scale and does not correspond to the freezing point of water; it was historically defined using a brine mixture.

Option C: 48 °F is above the freezing point; at this temperature, water is in liquid form.

Option D: 37 °F is slightly above freezing; water would be cold but not necessarily frozen under normal conditions.

Common Pitfalls:

Students sometimes confuse the zero points of Celsius and Fahrenheit scales. On Celsius, 0 °C corresponds to freezing, while on Fahrenheit, freezing occurs at 32 °F. Mixing these two values or assuming that 0 means freezing on all scales leads to incorrect answers. It helps to remember at least the pair (0 °C, 32 °F) for freezing and (100 °C, 212 °F) for boiling as anchor points.

Final Answer:

Pure water freezes at 32 °F on the Fahrenheit scale.