A company decides to make a novelty glass thermometer that uses water instead of mercury or alcohol. a) The thermometer would include a warning informing the user that it should not be exposed to temperatures below \(0^{\circ} \mathrm{C}\). Why? b) Suppose the thermometer is taken outside where the temperature is \(1^{\circ} \mathrm{C}\). Describe how the level of the water would change as it adjusts to the new temperature and how at some point it would behave very differently than a mercury-or alcohol-filled thermometer.

Understanding the thermal expansion of water is crucial for appreciating how water-based thermometers function. Thermal expansion is a physical property of substances to change in volume in response to changes in temperature.

When a substance heats up, the molecules inside it start moving faster and tend to move further apart, leading to an increase in volume, or expansion. Conversely, when a substance cools down, the molecules slow down and get closer together, which leads to a decrease in volume, or contraction.

Unique Behavior of Water

Water displays unique behavior when it comes to thermal expansion. Typically, most liquids contract when cooled; however, water contracts only until it reaches approximately 4 degrees Celsius. As it cools further below this point, instead of continuing to contract, water begins to expand until it reaches its solid state at 0 degrees Celsius. This anomalous expansion is due to the formation of a structured, hexagonal lattice in ice, which occupies more volume than liquid water.

Considerations for Water Thermometers

For a water-based thermometer, this atypical expansion can cause the liquid level to lower more gradually as the water cools, until reaching approximately 4 degrees Celsius. Below this, the expansion would misleadingly suggest an increase in temperature. This could lead for the liquid to potentially climb up the tube instead of descending, which makes water an inaccurate liquid for thermometry for temperatures close to its freezing point.

The freezing point of water is a critical concept in understanding why a company would warn against using a water-based thermometer in freezing temperatures. At 0 degrees Celsius (32 degrees Fahrenheit), the liquid state of water transitions to a solid - ice.

Most substances when freezing, contract in volume due to the decreased motion of their molecules. However, water once again is an exception. When water crystallizes and turns into ice, it expands by approximately 9%.

Impact on Thermometers

This expansion has significant implications for water-filled thermometers. Since the water would freeze and expand in sub-zero temperatures, the glass enclosure of the thermometer might not withstand the pressure from the expanding ice, leading to potential breakage. This leads to not only inaccurate readings but also a risk of shattered glass and spillage, which is why such thermometers are not advised for use in environments that can reach freezing temperatures.

To fully understand the operational differences between water-filled and other types of thermometers, a comparison between mercury and alcohol thermometers becomes necessary. Both mercury and alcohol are commonly used in thermometers due to their reliable thermal expansion properties that are much more predictable than water's.

Mercury Thermometers

Mercury is a metal that is liquid at room temperature and expands consistently with heat. This predictable expansion makes it very suitable for precision thermometers. However, due to the toxic nature of mercury, its use is being phased out for safety reasons.

Alcohol Thermometers

Alternatively, alcohol thermometers, usually filled with a colored ethanol or methanol solution, also provide consistent expansion and contraction in response to temperature variation and are safe to use. Unlike water, both mercury and alcohol do not have a point at which they expand upon further cooling, making them more reliable for a broader temperature range.
For standard applications, either mercury or alcohol thermometers offer precision and safety that cannot be matched by water-based thermometers, partly because there's no risk of freezing and breaking at low temperatures and partly due to their uniform behavior in expansion and contraction across a wide spectrum of temperatures.