Key Concepts

Heating a substance causes molecules to rate up and also spread slightly additional apart, occupying a larger volume that outcomes in a diminish in density.Cooling a substance reasons molecules to slow down and also get slightly closer together, occupying a smaller volume that results in an increase in density. Hot water is much less dense and will to rise on room-temperature water.Cold water is much more dense and will sink in room-temperature water.

You are watching: Is hot water heavier than cold


Students location hot and cold fancy water into room-temperature water. Castle observe the the hot water floats top top the room-temperature water and also the cold water sinks. Students will combine the principles of temperature, molecular motion, and density to discover that hot water is less dense than room-temperature water and that cold water is more dense.


Students will be able to explain, on the molecular level, just how heating and also cooling affect the thickness of water.


Download the student task sheet, and also distribute one every student once specified in the activity. The task sheet will certainly serve as the “Evaluate” component of each 5-E lesson plan.


Make sure you and also your student wear effectively fitting goggles.

About this Lesson

In this lesson, friend can aid students attach some of the concepts about density to principles from thing 1. In chapter 1, students experienced that warm increases molecule motion. This raised motion competes v the attractions between molecules, bring about the molecules to relocate a small further apart. They additionally saw that together a problem is cooled, molecules sluggish down and also their attractions lug them closer together. These concepts can additionally be used to the principle of density.

Materials for Each Group

Cold water (colored blue) in foam cup warm water (colored yellow) in foam cup Room temperature water in clean plastic cup (colorless)2 droppers

Materials for the Demonstration

Hot water (colored yellow)Cold water (colored blue)2 identical clear baby food jarsWater-resistant map (from a deck the cards or laminated table of contents card)Paper towels

Do a show to present that warm water floats on cold water.

Tell students that in thing 3, they have seen that various substances have different densities. In this activity, they will view that the exact same substance deserve to have various densities at various temperatures.

Tell students that you room going to try to place one jar filled with warm colored water upside under over one more jar v cold fancy water.

Ask student to do a prediction:

Do friend think the hot and cold water will mix or stay separate?

Either follow the procedure listed below or project the video clip for students. If you decide to do the demonstration, you might want to clock the video an initial in order to see just how to collection the jars up.

Project the video Hot Water top top Cold Water.


Hot water (about 50 °C, fancy yellow)Cold water (about 5 °C, colored blue)2 similar clear infant food jarsWater-resistant card (from a deck that cards or laminated table of contents card)Paper towels


Hot water ~ above topCompletely fill a infant food jar with hot tap water and add 2 fall of yellow food coloring. Fully fill an additional baby food jug with an extremely cold water and add 2 drops of blue food coloring. Line the water in both jars so the the colour is well-mixed in both. Place the cold water jug on a paper towel. Host a water-resistant card over the optimal of the warm water jar.

While stop the card against the jar opening, carefully turn the jar upside down.

With the card still in place, position the seasoned of hot water directly over the jar of cold water so that the tops heat up exactly. Slowly and carefully remove the card so the the hot water seasoned sits directly on top of the cold water jar.

Expected results

Although removed the map may result in a small mixing or spilling, the warm yellow water will remain in the optimal jar and the cold blue water will remain in the bottom jar.

Ask students:

Why carry out you think the hot water continued to be on optimal of the cold water?Students must realize the there is a density difference in between hot and also cold water. Warm water is less thick so the floats top top the denser cold water.

Ask students to do a prediction:

What might happen if you put the cold blue water on peak of the hot yellow water and also then gotten rid of the card? Cold water ~ above topExplore

Have students shot adding cold and also hot water to room-temperature water.

Question come investigate

Is over there a thickness difference in between hot and cold water?

Materials because that each group

Cold water (colored blue) in foam cup hot water (colored yellow) in foam cup Room-temperature water in clean plastic cup (colorless)2 droppers

Teacher preparation

Add ice cream to water come make an extremely cold water. Half-fill one foam cup v cold water (no ice cream cubes) and another with hot water because that each group.Add 2 drops of yellow food coloring to the warm water and 2 autumn of blue food coloring come the cold water.Fill a clear plastic cup about ⅔ the the method with room-temperature water.Distribute the collection of 3 cup to each group.


Fill one dropper with blue cold water. Bag the finish of the dropper around halfway into the colorless room-temperature water.

While observing indigenous the side, very gently squeeze the dropper so the the cold water gradually flows into the room-temperature water. Fill another dropper with yellow hot water. Poke the end of the dropper around halfway into the room-temperature water. When observing from the side, really gently squeeze out the dropper so the the warm water progressively flows into the room-temperature water. Record your observations on the activity sheet.

Expected results

The cold blue water will flow down and collect in ~ the bottom the the room-temperature water. The warm yellow water will rise and also collect at the surface.

Discuss student observations.

Ask students:

About cold waterWhat did you notification when you put the cold blue water in room-temperature water? The cold water sank in the room-temperature water.Is cold water more, less, or the same thickness as room-temperature water?Cold water is more dense than room-temperature water.About warm waterWhat walk you notice when you inserted the warm yellow water in room-temperature water? The warm water floated come the surface ar in the room-temperature water.Is warm water more, less, or the same density as room-temperature water?Hot water is less dense than room-temperature water.Extend

Do a demonstration to present students how thick cold water causes mixing.

Tell students that in winter, ice cream can kind on the top of ponds and also lakes. In the spring as soon as the ice melts, the cold water sinks. This causes mixing indigenous the bottom which brings nutrients as much as the surface. Phone call students that you will version this process.


Room-temperature water ice cubes2 identical tall clear plastic cupsSmall cupFood coloring, any color other than yellowDropperSheet of plain white paper


Fill 2 tall clear plastic cups about ⅔ that the method with room-temperature water.Place about 15 autumn of food coloring into a tiny empty cup. Use a dropper to choose up the food coloring. Then carefully push the dropper into the water until the tip of the dropper is near the bottom that the cup. Really gently squeeze the dropper therefore that every one of the food coloring gradually flows come the bottom of the cup. Then carefully remove the dropper to stop food coloring native mixing into the water. (It is yes if a tiny coloring gets combined in the water.)Repeat actions 2–4 because that the various other cup that water. Gently place two ice cubes in the water in one of the cups. (Avoid agitating the water.)Place a item of white record behind every cup and also observe.

See more: The Diffusion Of Water Molecules Across A Differentially Permeable Membrane Is Termed


Expected results

The colour in the cup v the ice will relocate up indigenous the bottom and also begin to mix transparent the water. The coloring in this cup will mix faster than the coloring in the cup without ice.

Ask students:

The food colour mixed an ext quickly in the cup that had actually the ice. Use what you know around the density of water at various temperatures to describe why this happened. Ice cream is around 0 °C and the water in the cup is around 20 °C. Together the ice cream melts, the water from the melted ice is chillier than the water roughly it. This cooler water is also more dense, for this reason it sink to the bottom. This sinking water pushes the food coloring the end of the way, resulting in mixing.