Key Concepts

The way a thermometer works is an instance of heating and also cooling a liquid. Once heated, the molecule of the liquid in the thermometer relocate faster, bring about them to get a little further apart. This results in movement up the thermometer.When cooled, the molecule of the fluid in the thermometer relocate slower, resulting in them to obtain a small closer together. This outcomes in movement down the thermometer.

You are watching: What is the red stuff in thermometers

Summary

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

Objective

Based on experimental observations, students will describe, on the molecule level, why the fluid in a thermometer go up when 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 activity sheet will serve as the “Evaluate” component of every 5-E lesson plan.

Safety

Be sure you and also the college student wear effectively fitting goggles.Students need to use care when handling hot tap water.When using isopropyl alcohol, read and follow every warnings top top the label. Isopropyl alcohol is flammable. Save it away from any type of flames or spark sources.

Materials because that Each Group

Student thermometerMagnifierCold waterHot water (about 50 °C)

Notes about the materials

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


Explore

Do an activity to investigate what provides the liquid in a thermometer walk up and down.

Question to investigate

What renders the liquid in a thermometer walk up and down?

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Materials for each group

Student thermometerMagnifierCold waterHot water (about 50 °C)

Procedure

Look very closely at the components of a thermometer.

Look very closely at her thermometer. The liquid within is more than likely a kind of alcohol that’s to be dyed red.

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Practice reading the temperature in °C by having your eye in ~ the exact same level as the peak of the red liquid. What is the temperature?

Use a magnifier come look very closely at the thermometer native the front and from the side. Look in ~ the bulb and also the thin pipe which save on computer the red liquid.

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

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

Place the thermometer in hot water and also watch the red liquid. Save it in the warm water until the fluid stops moving. Document the temperature in °C.

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

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Expected results

The red liquid goes increase in warm water and also down in cold water. Students will have actually an chance to said these observations to an explanation top top the molecule level, the why the fluid moves the means it does.

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

Record and discuss student observations

Give college student time ~ the task to record their monitorings by answering the complying with questions top top their task sheet. Once they have actually answered the questions, comment on their observations as a whole group.

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Based ~ above what friend know about the means molecules move in hot liquids, explain why the liquid in the thermometer go up once heated. Based upon what friend know around the method molecules move in cold liquids, define why the liquid in the thermometer go down once cooled. Why perform you think the tube which includes the red fluid is so thin?What execute you think is the objective of the larger outer tube?

When heated, the molecule of the red liquid inside the thermometer move faster. This motion competes v the attractions the molecules have for each other and also causes the molecules to spread a small further apart. They have nowhere come go various other than up the tube. As soon as the thermometer is put in cold water, the molecules sluggish down and also their attractions lug them a tiny closer with each other bringing them down the tube. The red liquid is contained in a an extremely thin tube so the a little difference in the volume that the liquid will be noticeable. The huge outer tube has two purposes—to safeguard the fragile inner tube and act as a magnifier to assist you better see the red liquid.