Marshmallow in a Syringe
10
Students will use marshmallows to study the effect that changing pressure has on the volume of a gas.
10
Materials
10
140-mL syringe with end cap
mini-marshmallow
Procedure
Take the syringe apart. Place one mini-marshmallow in the syringe and replace the plunger, pushing it down until it just reaches the marshmallow.
10
Place the cap or your fingertip over the tip of the syringe. Pull the plunger and observe the marshmallow. Release the cap or your finger and then pull the syringe back to allow more air.
10
Place the cap or your fingertip back on the syringe tip. Push the plunger and observe the marshmallow. If desired, repeat this several times. Remove the end cap, pull the syringe apart, and remove the marshmallow. Observe the marshmallow.
Explanation
A gas will expand to fill its container. When the pressure inside the syringe is reduced, by pulling the plunger out, the volume of air trapped in the marshmallow expands and the volume of the marshmallow increases.
10
The marshmallow is filled with air. Under reduced pressure, the air expands to fill the container, or syringe, causing the marshmallow to increase in size.
10
When the plunger is pushed in the pressure is increased causing the volume of the marshmallow to contract because the volume is decreasing. After removing the marshmallow from the syringe, the marshmallow may appear smaller in size than a normal mini-marshmallow.
10
This is a result of air escaping from the marshmallow when the pressure is decreased.
10
Moving Molecules
7
Students conclude that temperature affects the rate of movement of molecules in liquids and gases.
10
Materials
A clear glass beaker filled with hot water
A clear glass beaker filled with cold water
Food coloring
An eye dropper
Procedure
7, 10
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Fill the glass beakers with the same amount of water, one cold and one hot.
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Put one drop of food coloring into both glasses as quickly as possible.
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Ask students to watch what happens to the food coloring and record their observations
Explanation
The particles of liquids and gases are in constant motion. If you watch closely you will notice that the food coloring spreads faster throughout the hot water than in the cold.
7
The molecules in the hot water move at a faster rate because they have greater energy than those in the cold water. The molecules in the hot water spread the food coloring faster than the cold water molecules, which move slower. This type of movement is called diffusion.
7
Tissue in a Cup
6, 10
Students explore how you can keep a tissue dry underwater.
Materials
10
Large clear container, 2/3 full with water.
Clear plastic cup
Tissue paper
Food coloring
Tape
Pushpin
Procedure
6, 10
-
Add several drops of food coloring to the container 2/3 full of water.
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Poke a hole in the bottom of a plastic up using a pushpin.
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Crush a piece of the tissue paper and stuff it inside the plastic cup. Use the tape to hold the tissue in place. (Note: Make sure it does not cover the hole in the bottom of the cup.)
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Ask students to predict what will happen with the cup is submerged opening down into the water.
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Place your finger firmly over the hole at the bottom of the cup. With the open side down push the cup into the into the container of water.
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Keeping your finger over the hold withdraw the plastic cup from the water.
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Take out the tissue paper and let students determine if the tissue is dry or wet and report their observations.
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Leaving your finger off the hold on the bottom of the cup, repeat Steps 3-7.
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Ask students to explain why the tissue paper stayed dry in the first example.
Explanation
6, 10
Air is matter and it takes up space. Air is trapped in the cup when it is submerged with your finger over the bottom of the hole.
10
The air in the cup keeps the water out, so the tissue stays dry.
10
When the demonstration is repeated with the hole open air is pushed out of the cup through the hole as the water enters. Since air can escape, water fills the cup, and the tissue gets wet.
10
Cross-Curricular Integration
10
Discuss the historic use of the diving bell, which is another example of how air takes up space. The hollow diving bell was lowered into the water with the open end pointed down.
10
Air was trapped and passengers could use it to breathe when they worked underwater recovering sunken wreckage.
10
Boiling Water in a Syringe
2, 10
Water boils at 100°C right? Not always! Students will see a demonstration of water boiling at room temperature.
10
Materials
10
Water
250mL Beaker
Hot plate
Stopcock Syringe, without needle, 140-mL
Thermometer
Procedure
2
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Ensure the stopcock is open and fill the syringe with approximately 25 mL of the hot water.
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Hold the syringe so that the stopcock is up and carefully adjust the volume of the syringe to remove any air bubbles.
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Close the stopcock.
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Pull back on the plunger and observe the water.
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Eject the water from the syringe and repeat the activity with warm tap water.
Explanation
2, 10
Every liquid boils at the temperature at which its vapor pressure equals the pressure above its surface. By decreasing the pressure inside the syringe, water will boil below 100°C.
2
When the plunger is originally pulled the air pressure in the syringe falls below the water’s vapor pressure, causing the water to boil. If the plunger is held back long enough, the boiling slows and eventually stops.
2
As the water boils, the water vapor produced is pressurizing the area above it. The water will continue to boil until the pressure equals that of the vapor pressure or until there is no liquid left.
2
Disappearing Air Freshener
10
Students will discover how air freshener evaporates from a liquid gel to a gas.
10
Materials
10
1 solid air freshener
Balance
Procedure
10
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Place a closed air freshener on the balance and record the mass.
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Leave the air freshener open and record its mass each day for 5 days.
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Have students graph their data and discuss observations.
Explanation
Air fresheners are made of a gel that contains carrageenan, water, and small amount of liquid fragrance. The solid air fresher undergoes slow evaporation, which allows the liquid fragrance to be released.
10
