Temperature and Density | Chapter 3: Density | Middle School Chemistry
Students will combine the concepts of temperature, molecular motion, and density to learn that hot water is less dense than room-temperature water and that. Temperature Effects on Density. Density. Density is the mass of any material per unit volume. Gases always have much lower density than the condensed. That is, temperature rise lowers the density, and lowering temperature will Originally Answered: What is the relation between density and temperature?.
Within a particular phase, how does the density depend on temperature? Remember that temperature is related to the average kinetic energy of the atoms or molecules within the substance.
Density - Wikipedia
Pure Water The density of liquid water is approximately 1. Let's look at the density of water at 25 deg C and compare that to a higher temperature, 80 deg C.Temperature and Density
The density decreases from 0. This makes sense because, as heat is added to the liquid water, there is greater kinetic energy of the molecules and there are also more vibrations of the water molecules. Together these mean that each H2O unit in liquid water takes up more space as the temperature increases. We see the same trend in going from liquid water at 25 deg C 0. Density increase as the temperature decreases.
Temperature Affects Density
Below 4 deg C, however, the density decreases again. How can we explain this? Remember that liquid water and solid water have the same network of bonds. Liquid water at 25 deg is so rapidly breaking bonds between H2O units and reforming them that extra water molecules get trapped inside the water lattice.
This is the reason why liquid water is more dense than solid water. The bonds in water break more slowly as temperature decreases and the structure tend to trap fewer extra water molecules. Expected results The cold blue water will immediately fall into the hot yellow water causing mixing. The water will quickly become green throughout.
Why do you think the hot and cold water mixed when the cold water was placed on top? When the cold water is placed on top, the colors mix because the cold water is more dense and sinks in the hot water. Give each student an activity sheet.
Students will record their observations and answer questions about the activity on the activity sheet. The Explain It with Atoms and Molecules and Take It Further sections of the activity sheet will either be completed as a class, in groups, or individually depending on your instructions. Look at the teacher version of the activity sheet to find the questions and answers. Explore Have students try adding cold and hot water to room-temperature water.
Question to investigate Is there a density difference between hot and cold water?
Temperature Effects on Density
Materials for each group Cold water colored blue in foam cup Hot water colored yellow in foam cup Room-temperature water in clear plastic cup colorless 2 droppers Teacher preparation Add ice to water to make very cold water. Half-fill one foam cup with cold water no ice cubes and another with hot water for each group.
Add 2 drops of yellow food coloring to the hot water and 2 drops of blue food coloring to the cold water. Distribute the set of 3 cups to each group.
Procedure Fill one dropper with blue cold water. Poke the end of the dropper about halfway into the colorless room-temperature water. While observing from the side, very gently squeeze the dropper so that the cold water slowly flows into the room-temperature water. Fill another dropper with yellow hot water.