Key Concepts

The means a thermometer functions is an instance of heating and cooling a liquid. As soon as heated, the molecules of the liquid in the thermometer move faster, leading to them to acquire a little further apart. This outcomes in motion up the thermometer.When cooled, the molecule of the fluid in the thermometer relocate slower, leading to them to obtain a tiny closer together. This outcomes in movement down the thermometer.

You are watching: What is the red liquid in thermometers

Summary

Students will certainly look carefully at the components of a thermometer. After ~ placing a thermometer in hot and also cold water, students will look in ~ molecular version animations that the fluid in a thermometer. Students will certainly then attract a version of the molecules of a thermometer after ~ it has actually been inserted in hot and also then cold water.

Objective

Based on speculative observations, students will certainly describe, ~ above the molecular level, why the fluid in a thermometer walk up once it is heated and down as soon as it is cooled.

Evaluation

Download the student activity sheet, and also distribute one per student once specified in the activity. The task sheet will certainly serve as the “Evaluate” ingredient of each 5-E class plan.

Safety

Be sure you and also the college student wear properly fitting goggles.Students must use care when handling hot tap water.When using isopropyl alcohol, read and also follow all warnings on the label. Isopropil alcohol is flammable. Keep it far from any flames or spark sources.

Materials for Each Group

Student thermometerMagnifierCold waterHot water (about 50 °C)

Notes about the materials

Student thermometers are accessible from Sargent Welch (WL5679), Flinn clinical (AP5406) and also other suppliers.


Explore

Do an activity to inspection what makes the fluid in a thermometer go up and also down.

Question to investigate

What makes the liquid in a thermometer go up and down?

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Materials for each group

Student thermometerMagnifierCold waterHot water (about 50 °C)

Procedure

Look closely at the parts of a thermometer.

Look carefully at her thermometer. The liquid inside is most likely a form of alcohol that’s to be dyed red.

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Practice analysis the temperature in °C by having your eye at the exact same level together the peak of the red liquid. What is the temperature?

Use a magnifier to look very closely at the thermometer from the front and also from the side. Look in ~ the bulb and the thin pipe which contain the red liquid.

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Put your thumb or finger ~ above the red bulb and see if the red fluid moves in the slim tube.

Observe the red fluid in the thermometer once it is heated and also cooled.

Place the thermometer in hot water and also watch the red liquid. Store it in the hot water till the liquid stops moving. Document the temperature in °C.

Now placed the thermometer in cold water. Save it in the cold water until the liquid stops moving. Record the temperature in °C.

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Expected results

The red fluid goes increase in warm water and down in cold water. College student will have an chance to relate these observations to one explanation on the molecule level, of why the liquid moves the way it does.

If you have time, you can have students pick a temperature somewhere between the temperature the cold water and hot water and also then effort to combine an amount of hot and also cold water to achieve that temperature in one try. They deserve to see how close they have the right to get.

Record and discuss college student observations

Give college student time ~ the activity to record their monitorings by comment the adhering to questions top top their task sheet. When they have answered the questions, discuss their observations as a totality group.

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Based on what you know around the means molecules relocate in hot liquids, describe why the liquid in the thermometer walk up as soon as heated. Based on what you know around the means molecules relocate in cold liquids, explain why the fluid in the thermometer goes down as soon as cooled. Why do you think the tube which contains the red fluid is therefore thin?What do you think is the function of the bigger outer tube?

When heated, the molecules of the red liquid inside the thermometer relocate faster. This activity competes with the attractions the molecules have actually for each other and also causes the molecules to spread a small further apart. They have actually nowhere to go various other than increase the tube. When the thermometer is inserted in cold water, the molecules slow down and also their attractions carry them a small closer together bringing them under the tube. The red liquid is had in a very thin tube so that a little difference in the volume that the liquid will certainly be noticeable. The big outer tube has actually two purposes—to safeguard the breakable inner tube and act as a magnifier to assist you much better see the red liquid.