Hot Water and Thermometers: A Study of Mercury
In Activity 3.5: Observing Temperature Change in Hot Water, you’ll explore how mercury in a thermometer behaves and learn about the differences between clinical and laboratory thermometers.
Objective
To understand how mercury in thermometers responds to temperature changes and the practical differences between two types of thermometers.
Materials Needed
- A beaker or mug
- Hot water
- A laboratory thermometer
Steps to Follow
- Prepare Hot Water: Pour hot water into a beaker or mug.
- Measure Temperature: Insert the laboratory thermometer into the water. Ensure the bulb is immersed but not touching the sides or bottom of the container.
- Observe Mercury: Wait until the mercury inside the thermometer stabilises and note the temperature.
- Remove and Observe: Take the thermometer out of the water and watch what happens to the mercury level.
Expected Observations
- The mercury level rises in the hot water and becomes steady when it reaches the water’s temperature.
- When you remove the thermometer from the water, the mercury level starts to fall.
Understanding the Concepts
- Mercury’s Behavior: Mercury expands when heated and contracts when cooled. In hot water, it expands and rises. Once removed, it cools and contracts, causing the level to drop.
- Laboratory vs. Clinical Thermometers: The laboratory thermometer must stay in the substance to measure its temperature accurately. In contrast, a clinical thermometer, which is used to measure body temperature, has a kink near the bulb to prevent the mercury from falling immediately, allowing you to read the temperature outside the body.
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Conclusion
This activity teaches you about the properties of mercury in thermometers and the functional differences between laboratory and clinical thermometers. You learn that mercury responds directly to temperature changes and why certain types of thermometers are suited for specific measurements.
Key Points
- Mercury reacts to temperature changes by expanding or contracting.
- A laboratory thermometer’s reading changes immediately when removed from a substance.
- Clinical thermometers have a special design (a kink) to keep the mercury level steady for a short time for easy reading.
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