Look at the bulb and the thin tube which contain the red liquid. Place the thermometer in hot water and watch the red liquid. Keep it in the hot water until the liquid stops moving. Now put the thermometer in cold water.
Keep it in the cold water until the liquid stops moving. The red liquid goes up in hot water and down in cold water. Students will have an opportunity to relate these observations to an explanation on the molecular 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 of cold water and hot water and then attempt to combine an amount of hot and cold water to achieve that temperature in one try.
They can see how close they can get. Give students time after the activity to record their observations by answering the following questions on their activity sheet.
Once they have answered the questions, discuss their observations as a whole group. When heated, the molecules of the red liquid inside the thermometer move faster. This movement competes with the attractions the molecules have for each other and causes the molecules to spread a little further apart. They have nowhere to go other than up the tube. When the thermometer is placed in cold water, the molecules slow down and their attractions bring them a little closer together bringing them down the tube.
The red liquid is contained in a very thin tube so that a small difference in the volume of the liquid will be noticeable. The large outer tube has two purposes—to protect the fragile inner tube and act as a magnifier to help you better see the red liquid. Note: Alcohol molecules are composed of different atoms, but in the model shown in the animation the molecules are represented as simple red spheres.
Show the molecular model animation Heating and Cooling a Thermometer. Point out that when the thermometer is heated, the molecules move faster, get slightly further apart, and move up the tube. When the thermometer is cooled, the molecules move more slowly, get closer together, and move down the tube. Help students realize that the attractions the molecules in the thermometer have for each other remain the same whether the thermometer is heated or cooled.
The difference is that when heated, the molecules are moving so fast that the movement competes with the attractions, causing the molecules to move further apart and up the tube. When cooled, the movement of the molecules is slower and does not compete as much with the attractions the molecules have for one another. This is why the molecules in the thermometer move closer together and down the tube.
Project the image Molecules in A Thermometer. In the drawing, lines have been added to indicate the level of the liquid in each tube. In reality, there is no line. Students should draw circles representing molecules all the way up to the line drawn in each tube. Some thermometers are made with mercury, a metallic liquid that reacts in a very specific way to changes in temperature, and is therefore ideal for use as a temperature measuring tool.
Mercury is a great tool for measuring changes in heat, but it is a dangerous material on its own. To that effect, some states even have limits or bans on the sale and use of mercury thermometers.
The problem is that mercury in high concentration is poisonous to humans, wreaking serious havoc on the immune system or causing memory problems.
All matter, be it a solid, liquid or gas, is made up of atoms--extremely tiny particles. These particles all behave similarly with different levels of heat. One of the most well-known examples of this is water: at a certain point, 32 degrees Fahrenheit, it freezes and turns into ice; at another point it boils and begins to turn into gas degrees F. As water gets colder, its atoms slow down, eventually coming to a stop to form ice.
As it gets hotter, the atoms start moving extremely fast, eventually turning into a vapor. Mercury behaves similarly, although its freezing and boiling points are very different from those of water. Mercury can go colder and get hotter than water while remaining liquid. The narrow bore of te capillary tube makes the thermometer more sensitive. This is because a small expansion of the mercury in the bulb will cause a big change in the length of the mercury thread.
The bulb is made of thin glass so that heat can be conducted quickly to the liquid. Although mercury thermometers have been mostly phased out of daily home use, the tool, which was invented in the s by Gabriel Daniel Fahrenheit, remains a standard measuring device for many industries, including regulating the temperature of a chemical concoction being made in an industrial lab, and monitoring the ….
A broken mercury-containing thermometer can be toxic if the vapors are inhaled. The risk of poisoning from touching or swallowing mercury from a broken thermometer is low if appropriate clean-up measures are taken. If you break a mercury thermometer or light bulb, a small amount of liquid mercury may spill out.
Liquid mercury can separate into small beads, which can roll some distance away. The mercury may also evaporate into vapour. However, this small amount of mercury is extremely unlikely to cause problems for your health. Wipe the area with a damp cloth. Put collected mercury and the cloth in the same bag and seal it. In case mercury has been spilled over the cloth, dispose of them in a sealed bag. Do not wash them or put them in washing machine.
Some thermometers and light bulbs contain very small amounts of mercury.
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