Racing Molecules Lab
Hypothesis
If the temperature of a liquid increases, then the kinetic energy will _______________________.
Materials
 3 cups
 Thermometer
 Food Dye Tablets
 Water (at various temperatures)
Procedure
1. Empty the cups and label them “1”, “2”, and “3”.
2. Fill the “1” cup with very cold water.
3. Measure the temperature of the water and record the temperatures in the table below.
4. Get your timer ready. At the same time, drop one tablet of food coloring the cup and
immediately start the timer.
5. Watch the food coloring spread out in the water and write down your observations after 30
seconds, 1 minute, and 2 minutes in the following charts. Pay special attention to how streaky
the food coloring is and whether it is spread out evenly within the water.
6. Fill the “2” cup with lukewarm (slightly warm) water.
7. Repeat step 3-5
8. Fill the “3” cup with very warm water.
9. Repeat steps 3-5
Data
Cup
Initial
Temp.
1
2
3
Cup
1
2
3
Observation
30 seconds
Sketch
Cup
Observation
1 minute
Sketch
Observation
2 minutes
Sketch
1
2
3
Cup
1
2
3
Analysis
1. How did the temperature of the water affect the time it took for the food coloring to spread
out?
2. Temperature is a measure of how fast the molecules are moving within the cup of water. How
does this explain what you observed in this experiment?
3. As the temperature increases, does the speed of its molecule increase or decrease?
4. As the speed of water molecules increases, does the time it takes for the food coloring to
spread out increase or decrease? Why do you think that is?
5. On a molecule level, explain the main difference between hot and cold.
6. Read your hypothesis, explain why it was correct or incorrect.
Math Connection
1. Using a mathematical relationship determined by scientist, you can calculate approximately
how fast the water molecules are moving within each cup of water.
𝐒𝐩𝐞𝐞𝐝 = 𝟑𝟕 √𝐓 + 𝟐𝟕
Where T is the water temperature in degrees Celsius. This relationship gives you an answer in
meters per second.
Use the equation to calculate that average speed of the water molecules at the three
different temperatures of water that you measured. Record the speeds in the following chart.
Speed of Water Molecules
Cup
1
2
3
Temperature of Water (C)
Speed (in meters per second)
2. How do these speeds compare to the speed of a car (55 mph = 24.5872 m / s)? The speed of
light (299,792,458 m / s)? The speed of sound (340.29 m / s)?