ice melting in salt water experiment

Adventures in Oceanography and Teaching

Dr. mirjam s. glessmer, experiment: ice cubes melting in fresh water and salt water.

Explore how melting of ice cubes floating in water is influenced by the salinity of the water. Important oceanographic concepts like density and density driven currents are visualized and can be discussed on the basis of this experiment.

This hands-on experiment is suited for many different audiences and can be used to achieve a wealth of different learning goals. Audience ranges from first-graders over undergraduates in physical oceanography to outreach activities with the general public. Depending on the audience, this activity can be embedded in very different contexts: For children, either in their physics teaching to motivate learning about concepts like density, or in the context of learning about the climate system and ocean circulation. For college/university students the activity can either be used in physics teaching to get a different view on density; in oceanography/Earth science to talk about ocean circulation and processes that are important there; to motivate the scientific process; or to practice writing lab reports (you can be sure that students will at some point be tasting the water to make sure they didn’t accidentally swap the salt water and fresh water cup – a great teachable moment for a) Never putting anything in your mouth in a laboratory setting, and b) Always documenting exactly what you are doing because stuff that you think you will definitely remember obviously isn’t remembered that clearly after all). For the general public, this is typically a stand-alone activity.

Skills and concepts that students must have mastered

It helps if the concept of density is known, but the experiment can also be used to introduce or deepen the understanding of the concept.

How the activity is situated in the course

I use this activity in different ways: a) as a simple in-class experiment that we use to discuss the scientific method, as well as what needs to be noted in lab journals and what makes a good lab report, or density-driven circulation; b) to engage non-majors or the general public in thinking about ocean circulation, what drives ocean currents, … in one-off presentations.

Content/concepts goals for this activity

Students learn about concepts that are important not only in physical oceanography, but in any physical or Earth science: density in general; density of water in particular, depending on the water’s temperature and salinity; how differences in density can drive currents both in the model and in the world ocean; how different processes acting at the same time can lead to unexpected results; how to model large scale processes in a simple experiment. After finishing the activity, they can formulate testable hypotheses, are able to reason based on density how a flow field will develop and they can compare the situations in the cups to the “real” ocean.

Higher order thinking skills goals for this activity

Students learn about and practice the use of the scientific method: formulation of hypotheses, testing, evaluating and reformulating.

Other skills goals for this activity

Students practice writing lab reports, making observations, working in groups.

Description and Teaching Materials

(per group of 2-4 students):

• 1 clear plastic cup filled with room-temperature salt water (35psu or higher, i.e. 7 or more tea spoons of table salt per liter water), marked as salt water (optional)
• 1 clear plastic cup filled with room-temperature fresh water, marked as fresh water (optional)
• 2 ice cubes
• liquid food dye either in drop bottle, with a pipette or with a straw as plunging syphon

Description

Before the experiment is started, students are asked to make a prediction which ice cube will melt faster, the one in salt water or the one in fresh water. Students discuss within their groups and commit to one hypothesis. Students then place the ice cubes into the cups and start a stop watch/note the time. Students observe one of the ice cube melting faster than the other one. When it becomes obvious that one is indeed melting faster, a drop of food dye can be added on each of the ice cubes to color the melt water. Students take the time until each of the ice cubes has melted completely.

The ice cube in the cup containing the fresh water will melt faster, because the (fresh) melt water is colder than the room-temperature fresh water in the cup. Hence its density is higher and it sinks to the bottom of the cup, being replaced by warmer waters at the ice cube. In contrast, the cold and fresh melt water in the salt water cup is less dense than the salt water, hence it forms a layer on top of the salt water and doesn’t induce a circulation like the one in the fresh water cup. The circulation is clearly visible as soon as the food dye is added: While in the freshwater case the whole water column changes color, only a thin meltwater layer on top of the salt water is colored (for clarification, see images in the presentation below)

Teaching Notes and Tips

Students usually assume that the ice cube in salt water will melt faster than the one in fresh water, “because salt is used to de-ice streets in winter”. Have students explicitly state their hypothesis (“the one in salt water will melt faster!”), so when they measure the time it takes the ice cubes to melt, they realize that their experiment does not support their hypothesis and start discussing why that is the case. ( Elicit the misconception, so it can be confronted and resolved! )

My experience with this experiment is that all groups behave very consistently:

• At least 80% of your audience will be very sure that the ice cube in salt water will melt faster than the one in fresh water. The other 20% will give the correct hypothesis, but only because they expect a trick question, and they will most likely not be able to come up with an explanation.
• You can be 100% sure that at least in one group, someone will say “oh wait, which was the salt water again?” which hands you on a plate the opportunity to say “see — this is a great experiment to use when talking about why we need to write good documentations already while we are doing the experiment!”
• You can also be 100% sure that in that group, someone will taste the water to make sure they know which cup contains the salt water. Which lets you say your “see — perfect experiment to talk about lab safety stuff! Never ever put things in your mouth in a lab!”
• At  EMSEA14 , people asked  what would happen if the ice cubes were held at the bottom of the beaker .
• At a workshop on inquiry-based learning, people asked what the dye would do if there was no ice in the cups, just salt water and fresh water. Perfect opportunity to say “try! Then you’ll know! And btw — isn’t this experiment perfect to inspire the spirit of research (or however you would say that in English – “Forschergeist” is what I mean!). This is what you see in the pictures in this blogpost.

It is always a good idea to have plenty of spare ice cubes and salt/fresh water at room temperature ready so people can run the experiment again if they decide to either focus on something they didn’t observe well enough the first time round, or try a modified experiment like the ones described above.

A reviewer of this activity asked how easily students overcome the idea that water in the cup has to have just one temperature. In my experience this is not an issue at all – students keep “pointing” and thereby touching the cups, and in the thin-walled plastic cups I typically use the temperature gradient between “cold” melt water and “warm” salt water is easily felt. The (careful!) touching of the cups can also be explicitly encouraged.

Different ways to use this experiment

This experiment can be used in many different ways depending on the audience you are working with.

• Demonstration : If you want to show this experiment rather than having students conduct it themselves, using colored ice cubes is the way to go ( see experiment here ). The dye focuses the observer’s attention on the melt water and makes it much easier to observe the experiment from a distance, on a screen or via a projector. Dying the ice cubes makes understanding much easier, but it also diminishes the feeling of exploration a lot – there is no mystery involved any more. And remember in order for demonstrations to increase the learning outcome , they need to be embedded in a larger didactical setting, including forming of hypotheses before the experiment is run and debriefing afterwards.
• Structured activity : For an audience with little knowledge about physics, you might want to start with a very structured activity, much like the one described above. Students are handed (non-colored) ice cubes, cups with salt water and fresh water and are asked to make a prediction about which of the ice cubes is going to melt faster. Students test their hypothesis, find the results of the experiment in support with it or not, and we discuss. This is how I usually use this experiment in class ( see discussion here ).The advantage of using this approach is that students have clear instructions that they can easily follow. Depending on how observant the group is, instructions can be very detailed (“Start the stop watch when you put the ice cubes in the water. Write down the time when the first ice cube has melted completely, and which of the ice cubes it was. Write down the time when the second ice cube has melted completely. …”) or more open (“observe the ice cubes melting”).
• Problem-solving activity : Depending on your goals with this experiment, you could also consider making it a problem-solving activity: You would hand out the materials and ask the students to design an experiment to figure out which of the cups contains fresh water and which salt water (no tasting, of course!). This is a very nice exercise and students learn a lot from designing the experiment themselves .
• Open-ended investigation : In this case, students are handed the materials, knowing which cup contains fresh and salt water. But instead of being asked a specific question, they are told to use the materials to learn as much as they can about salt water, fresh water, temperature and density.As with the problem-solving exercise, this is a very time-intensive undertaking that does not seem feasible in the framework we are operating in. Also it is hard to predict what kind of experiments the students will come up with, and if they will learn what you want them to learn. On the other hand, students typically learn much more because they are free to explore and not bound by a specific instruction from you, so maybe give it a try?
• Problem-based learning : This experiment is also very well suited in a Problem-Based Learning setting, both to work on the experiment itself or, as we did, to have instructors experience how problem-based learning works so they can use it in their own teaching later. Find a suggested case and a description of our experiences with it  here.
• Inquiry-based learning : Similarly as with Problem-Based Learning, this experiment can be used to let future instructors experience the method of inquiry-based learning  from a student perspective. For my audience, people teaching in STEM, this is a nice case since it is close enough to their topics so they can easily make the transfer from this case to their own teaching, yet obscure enough that they really are learners in the situation.

Pro tip: If you are not quite sure how well your students will be able to cope with this experiment, prepare ice cubes dyed with food coloring and use them in a demonstration if students need more help seeing what is going on, or even let students work with colored ice cubes right from the start. If ice cubes and hence melt water are dyed right away, it becomes a lot easier to observe and deduct what is happening. Feel free to bring the photos or time lapse movie below as a backup, too!

Dyed ice cubes about to be put into fresh water (left) and salt water (right)

When the ice cubes start melting, it becomes very clear that they do so in different manners. In the left cup, the cold meltwater from the ice cube is denser than the lukewarm water in the cup. Hence it sinks to the bottom of the beaker and the water surrounding the ice cube is replaced by warmer water. On the right side, the lukewarm salt water is denser than the cold melt water, hence the cold meltwater floats on top, surrounding the ice cube which therefore melts more slowly than the one in the other cup.

The ice cube in the fresh water cup (left) is almost completely gone and the water column is fairly mixed with melt water having sunk to the bottom of the beaker. The ice cube in the salt water cup (right) is still a lot bigger and a clear stratification is visible with the dyed meltwater on top of the salt water.

And here a time-lapse movie of the experiment.

Another way to look at the experiment: With a thermal imaging camera!

Cold (dark purple) ice cubes held by warm (white-ish) fingers over room-temperature (orange) cups with water

After a while, both cups show very different temperature distributions. The left one is still room temperature(-ish) on top and very cold at the bottom. The other one is very cold on top and warmer below.

When you look in from the top, you see that in the left cup the ice has completely melted (and the melt water sunk to the bottom), whereas in the right cup there is still ice floating on top.

Depending on the audience I use this experiment with, the learning goals are very different. Therefore, no one assessment strategy can be used for all different applications. Below, I am giving examples of what are possible ways to assess specific learning goals:

– Students apply the scientific process correctly: Look at how hypotheses are stated (“salt melts ice” is not a testable hypothesis, “similar-sized ice cubes will melt faster in salt water than in fresh water of the same temperature” is).

– Students are able to determine what kind of density-driven circulation will develop: Suggest modifications to the experiment (e.g. ice cubes are made from salt water, or ice cubes are held at the bottom of the cups while melting) and ask students to predict what the developing circulation will look like.

– Students can make the transfer from the flow field in the cup to the general ocean circulation: Let students compare the situation in the cup with different oceanic regions (the high Arctic, the Nordic Seas, …) and argue for which of those regions displays a similar circulation or what the differences are (in terms of salinity, temperature, and their influence on density).

In general, while students run the experiment, I walk around and listen to discussions or ask questions if students aren’t already discussing. Talking to students it becomes clear very quickly whether they understand the concept or not. Asking them to draw “what is happening in the cup” is a very useful indicator of how much they understand what is going on. If they draw something close to what is shown on slide 28 of the attached slide show, they have grasped the main points.

Don’t worry, it is totally feasible to bring all the equipment you need with you to run the experiment anywhere you want. This is what we brought to EMSEA14 to run the workshop three times with 40 participants each:

What we brought to EMSEA14 to run workshops on the ice cubes melting in fresh and salt water experiment

In one big grocery bag:

• 4 ice cube trays
• 4 ice cube bags (backup)
• 2 thermos flasks (to store ice cubes)
• 1 insulating carrier bag (left)
• 4 empty 1.5l water bottles to mix & store salt water in
• 1 tea spoon for measuring salt
• 500g table salt
• 21 clear plastic cups for experiments
• 10 clear plastic cups to hand out ice cubes in
• 11 straws (as pipettes)
• 1 flask of food dye
• 11 little cups with lids to hand out food dye in
• nerves of steel (not shown :-))

And if you are my friend, you might also get the “ice cube special” — a pink bucket with all you will ever need to run the experiment! Below is what the ice cube experiment kit looks like that I made for Marisa, with labels and everything…

An “ice cube experiment” kit that I made for a friend. Want one, too?

References and Resources

This activity has been discussed before, for example here:

• http://www.lawrencehallofscience.org/comsci/pdfs/2_Teaching_and_Learning.pdf
• http://www.usc.edu/org/cosee-west/glaciers/Ice_Cube_ExptFINAL.pdf
• http://www.cesn.org/cosee_CD/web/activity/Melting_Ice.pdf

I have also written about it a lot on my blog, see posts tagged “ melting ice cubes experiment “.

P.S.: This text originally appeared on my website as a page. Due to upcoming restructuring of this website, I am reposting it as a blog post. This is the original version last modified on November 4th, 2015.

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12 thoughts on “ experiment: ice cubes melting in fresh water and salt water ”.

Pingback: Sea ice formation, brine release, or: What ice cubes can tell you about your freezer | Mirjam S. Glessmer

These are great ideas, too many people reach for the salt when they don’t need it.

Pingback: Melting ice cubes experiment published in kids’ journal Frontiers Young Minds | Dr. Mirjam S. Glessmer

Pingback: What’s #kitchenoceanography all about? | Dr. Mirjam S. Glessmer

Pingback: Fresh water or salt water? – Elin Darelius & team's scientific adventures

Pingback: On melting ice cubes and molecular diffusion of heat - Dr. Mirjam S. Glessmer

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Experiments With Salt Melting Ice

Teachers interested in using salt and ice experiments in the classroom can incorporate a range of theories and methods into lessons. Discuss the properties of salt and its effect on water, the influences on melting ice, or the creation of ice crystals in the winter. Using salt and ice to explore melting points allows students to develop an understanding of substances and their chemical reactions.

How can salt lower the freezing point of water?

This experiment involves students testing the properties and effects of salt on ice and water. Students need 2 cups of water, salt, ice cubes and access to a freezer. First put a tablespoon of salt into one of the cups of water, and place both cups into the freezer. Check each cup every 10 minutes and take a guess as to which cup's water will freeze first. Next, take two ice cubes out of the freezer and put them on a plate. Sprinkle some some salt on one of the ice cubes. Observe and record which ice cube melts the fastest. These two experiments allow students to determine that salt lowers the freezing point of water. Students can infer that salt water can still freeze, but the temperature must be colder than fresh water.

Thread the Ice

Demonstrate the properties of solids and liquids by using an experiment with water and ice. Students need an ice cube, a bowl, some thread and salt. Place the ice cube in the bowl and put the thread across the ice. Sprinkle some salt along the thread and on to the ice cube. Wait for two minutes, and carefully pull the ends of the thread. The thread is now frozen to the ice. The teacher can explain that liquid water has molecules that move around, while the molecules in the solid ice are fixed and do not move. Describe the process of ice melting in terms of the exchange of molecules due to temperature changes. The salt is diluted by the water that has melted off the ice, allowing the ice to capture some of the molecules of water which causes the ice to freeze around the thread.

Salt vs. Sugar: Melting Ice

Compare the effects of salt and sugar on water and ice. Students observe the properties of ice, and that salt speeds up the rate of ice melting compared to sugar or nothing. Students need three zip-lock bags, a teaspoon, ice cubes, salt, sugar and a plastic sheet to cover the work area. First label each zip-lock bag with either control, salt or sugar. Place an ice cube in each of the bags. Measure a teaspoon of salt and place it in the bag labeled salt. Measure a teaspoon of sugar and sprinkle it in the bag labeled sugar. Seal the bags and observe the three ice cubes in the different conditions. Students can infer which ice cube will melt the fastest by watching the transformation of each ice cube.

• CSIRO: Salt vs. Ice
• Project Labs: Ice cubes and salt

Cite This Article

Wehner, Amanda. "Experiments With Salt Melting Ice" sciencing.com , https://www.sciencing.com/experiments-salt-melting-ice-6497888/. 24 April 2017.

Wehner, Amanda. (2017, April 24). Experiments With Salt Melting Ice. sciencing.com . Retrieved from https://www.sciencing.com/experiments-salt-melting-ice-6497888/

Wehner, Amanda. Experiments With Salt Melting Ice last modified March 24, 2022. https://www.sciencing.com/experiments-salt-melting-ice-6497888/

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Does an ice cube melt faster in freshwater or saltwater?

May 22, 2024 By Emma Vanstone 1 Comment

This simple science demonstration uses only a few basic materials but demonstrates several scientific concepts and looks super impressive. Showing children the end result first is a great way to get them to start questioning and thinking about what’s happening and why.

There are two different things children can observe with this activity.

• How fast the ice cube melts in each glass.
• What happens to the ice cube water as it melts?

Adding salt to water increases its density. This means the melted water from the ice cube should sit on top of the salty water, as the water without salt has a lower density.

If you’ve ever made ice cream in a bag , you know that salt lowers the freezing point of water, so you might expect the salty water to melt the ice cube faster, but in our case, this didn’t happen.

Does ice melt faster in freshwater or saltwater?

You’ll need.

Two tall glasses

Ice cube tray

Food colouring

Instructions

Fill two segments of an ice cube tray with water and food colouring and place in a freezer until frozen.

Fill each glass to about 3 cm from the top with room temperature water.

Add two tablespoons of salt to one glass and stir until the salt has dissolved and the water is clear.

Place one ice cube into each glass and watch what happens.

You can see that in the glass containing salt, the ice cube melted more slowly, and the water from the melted ice cube mostly stayed near the top of the glass.

This is because the salty water underneath is denser than the ice cube water and food colouring, so the ice cube water sits on top of the salty water.

We expected the ice cube to melt faster in the salty water, but this didn’t happen. However, we noticed that the coloured water mixed with the freshwater quickly, forming a convection current. The cooler ice cube water sank to the bottom, and the warmer, less dense water rose up, creating a small current as the ice melted. This didn’t happen in the salty water. Some of the coloured ice cube water did sink, but it mostly stayed on the top, so it wasn’t warmed as much as the ice cube in the fresh water.

Extra Challenges

Repeat the activity using containers with one tablespoon of salt, two tablespoons of salt, three tablespoons of salt, and no salt.

Set children a challenge to work out which glass of water contains the most salt from four containers, each containing different amounts of dissolved salt.

More salt experiments

Use the cooling power of salt to chill a warm drink quickly !

Discover how salt melts snow .

Learn more about density with a salt lava lamp .

Find out about evaporation by making coloured salt crystals .

Science concepts

Heat Transfer

Last Updated on May 22, 2024 by Emma Vanstone

Safety Notice

Science Sparks ( Wild Sparks Enterprises Ltd ) are not liable for the actions of activity of any person who uses the information in this resource or in any of the suggested further resources. Science Sparks assume no liability with regard to injuries or damage to property that may occur as a result of using the information and carrying out the practical activities contained in this resource or in any of the suggested further resources.

These activities are designed to be carried out by children working with a parent, guardian or other appropriate adult. The adult involved is fully responsible for ensuring that the activities are carried out safely.

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May 23, 2024 at 9:14 am

Thanks Emma. Really enjoying your suggestions.

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Melting Ice Experiment

Physical sciences 2-ps1-4.

Construct an argument with evidence that some changes caused by heating or cooling can be reversed and some cannot.

Physical Sciences 5-PS1-1

Develop a model to describe that matter is made of particles too small to be seen.

Physical Sciences MS-PS1-4

Develop a model that predicts and describes changes in particle motion, temperature, and state of a pure substance when thermal energy is added or removed.

Physical Sciences HS-PS3-4

Plan and conduct an investigation to provide evidence that the transfer of thermal energy when two components of different temperature are combined within a closed system results in a more uniform energy distribution among the components in the system (second law of thermodynamics).

In this activity, students will predict, observe, and compare melt rates of ice under different temperature conditions and in different solutions.

• Cool and warm water
• Ice cubes (4-6 per group, uniform size and shape)
• Food coloring
• Thermometers
• Colander, mesh strainer, or other similar device
• Small bowls (2 per group)
• Cloth or paper towels
• (Optional) pitchers for pouring water
• (Optional) basin for catching poured water
• (Optional) funnels
• This activity requires flowing water. If available, a faucet with cold and warm water can be used. Otherwise, use pitchers with warm and cold water. However, note that the rate at which water is poured from a pitcher can vary greatly. Pouring through a funnel can help regulate the flow of water.
• Consider having towels on hand for cleaning up spills and splashes.
• Safety: Hot water can scald. Make sure students are using water that is below 110° F (43° C).
• Use the leftover water from this activity to water a plant or save it for another activity instead of dumping it down the drain.

The Greenland ice sheet is the second largest body of ice in the world right behind the Antarctic ice sheet. As the ice sheet melts, the water flows into the ocean, contributing to global sea level rise.

As glacier ice melts, some of the water can reach the ground below the ice, forming a river that channels glacier water into the ocean. As it flows into the ocean, this cold, fresh meltwater will rise above the warmer, salty ocean water because freshwater is less dense than salt water.

The rising cold water then draws in the warmer ocean water, melting the face of the glacier from the bottom up. This creates an overhang of ice, the edges of which will eventually break off in a process called calving, which quickly adds more ice to the ocean. As ocean waters warm, this calving process speeds up.

This narrated animation shows warm ocean water is melting glaciers from below, causing their edges to break off in a process called calving. Credit: NASA | Watch on YouTube

Understanding these different factors that contribute to Greenland's melting ice sheet is an important part of improving estimates of sea level rise. The Oceans Melting Greenland (OMG) mission was designed to help scientists do just that using a combination of water temperature probes, precise glacier elevation measurements, airborne marine gravity, and ship-based observations of the sea floor geometry. The mission, which ran from 2016 to 2022, provided a data set that scientists can now use to model ocean/ice interactions and improve estimates of global sea level rise.

Part 1: Still Water

Introduce or ask students what they know about glaciers, ice melt, and sea level rise. Consider using the lesson What’s Causing Sea-Level Rise? and having students read 10 Interesting Things About Glaciers from NASA's Climate Kids website prior to this activity. If necessary, remind students that glaciers are huge, long-lasting masses of ice sitting on landmasses that form over many years. Snow accumulates and compresses into glacier ice under the weight of newer layers of snowfall above. Glaciers are not to be confused with icebergs, which are large chunks of glaciers or ice sheets that have broken off and float freely in the ocean.

Tell students they are going to compare how quickly ice melts under different conditions. Ask students to predict what will happen to the ice and water temperature under the following conditions. Predictions can be relative (e.g., “Ice will melt faster in condition A”) or specific (e.g., “Ice will melt in X seconds in condition A”).

• Ice cube placed in a dish of room temperature water
• Ice cube placed in a dish of hot water
• Ice cube placed under flowing room temperature water
• Ice cube placed under flowing hot water

Fill one container with room-temperature water and a second container with hot water. Image credit: NASA/JPL-Caltech

As a class demonstration, or in groups of two to four students:

• Fill one dish with room temperature water.
• Measure and record the temperature.
• Gently place an ice cube in the dish and record how long it takes for the ice cube to melt. There should be enough water in the dish so the ice cube floats.
• Measure and record the water temperature after the ice has melted.

Place an ice cube in each container of water and time how long it takes the ice to melt. Image credit: NASA/JPL-Caltech

Repeat the procedure using hot water. These two steps can be done at the same time if students are able to monitor and record the melt time for both cubes of ice.

Ask students to share their results and observations.

Part 2: Flowing Water

Under a faucet of running water, or using water from a pitcher (see Management tip about using a funnel), complete the following as a demonstration or in groups of two to four students:

• Run the faucet and adjust as needed to get the water at the same room temperature as in the previous step. Record the temperature.

mage credit: NASA/JPL-Caltech

• Place an ice cube in a colander or mesh strainer and run it under the faucet, or pour water from the pitcher onto the ice cube. Record how long it takes to melt.

Image credit: NASA/JPL-Caltech

Repeat the procedure using hot water, matching the temperature from the earlier step.

Part 3: Salt and Freshwater

Mix water with food coloring and freeze into ice cubes (two per group or two as a class demo).

Tell students they are going to add a colored ice cube to a saltwater solution and to a freshwater solution and allow the ice to fully melt. Ask them to make predictions about what will happen.

In a clear beaker or plastic container, add 1 teaspoon of salt to 1 cup of water and stir until the salt is dissolved. Allow time for any water movement to stop.

Pour the same amount of freshwater into a clear beaker or plastic container. Allow time for any water movement to stop.

Gently add one ice cube to each container, taking care to not disturb the water too much.

Have students observe each container and take notes. It may be helpful for students to place a white sheet of paper behind the containers to see more details.

When the ice has melted, ask students to compare their observations to their predictions and develop hypotheses about the phenomena they observed.

Some food coloring in the container with the salty solution will mix with the salt water, but the majority of the coloring will be concentrated in the freshwater layer at the top. The top layer should be noticeably darker.

The cup on the left (with blue food coloring) contained ice melted in a saltwater solution while the one on the right (with the red food coloring) contained ice melted in a freshwater solution. Image credit: NASA/JPL-Caltech

If necessary, explain to students that because one container has salt water, and one has freshwater, the less dense meltwater floats on salt water but has the same density and mixes with the freshwater.

Connect this phenomenon to the movement of fresh meltwater from under a glacier into warm ocean water.

• Which ice cube melted fastest? Which melted slowest? How could these results be altered? Changing the flow rate and temperature of the water will change how quickly the ice melts.
• What do these results tell you about the melting of glaciers in different conditions? Currents of warm ocean water will melt glaciers faster than still water.
• What would happen to cold meltwater that flows out from under a glacier into salty ocean water? The freshwater will rise because of its lower density, drawing in warmer ocean water against the face of the glacier.
• Students should accurately measure and record temperature and melt times.
• High school chemistry students should accurately calculate what the final temperature of the water in the containers will be in Part 1 by using specific heat capacity.
• Ask students to investigate whether ice exposed to warm or room temperature air would melt more quickly or more slowly than ice exposed to still or flowing warm or room temperature water.
• Lower elementary: Ask students to predict what would happen if some of the water was removed from the containers in Part 1 and placed in the freezer. Freeze some of the water to confirm their predictions.
• Upper elementary: Remove some of the salt water from Part 3 and place it on a flat, non-porous surface to dry. Ask students to predict what will happen when the water evaporates. Repeat the process with freshwater. Allow water to dry overnight and compare predictions to observations of what occurred.
• Middle school: Ask students to draw or describe the changes in particle motion, temperature, and state(s) of matter at the beginning and end of their observations.
• High school: Using the known masses and temperatures of the ice cubes and water in Part 1, have students calculate the final temperature of the water in the room temperature bowl and the hot water bowl using the formula m 1 CΔT 1 = m 2 CΔT 2 . Then, have them compare their calculations to observed results.

About the Author

Lyle Tavernier

Educational Technology Specialist, NASA-JPL Education Office

Lesson Last Updated: Nov. 4, 2024

Explore the natural world through science and sustainability

How Does Salt Affect Ice? A Simple Science Experiment

Looking for a way to explain to your learners why salt is utilized to combat icy roadways and sidewalks? Check out this simple science experiment to demonstrate how salt affects the freezing point of water and how the over-utilization of salt can be harmful to the environment.

Every winter before a storm, large trucks rumble down the road through my neighborhood, spreading salt crystals over the pavement. My six-year-old was curious about why these trucks appeared before a storm and so I decided to not only tell him but to show him, with a simple science experiment.

The Simple Science of Water and Salt

To provide my kids with a bit of background information, I broke out my chemistry modeling set and gave them a brief description of what’s happening at the molecular level.

Water is a molecule that is made up of two elements: hydrogen and oxygen. Water, also written as H 2 O, freezes at 0℃ or 32℉. However, when a compound like sodium chloride, NaCl, what we commonly refer to as salt, is dissolved in water, something interesting happens. The salt compound breaks apart into sodium and chlorine ions and prevents the water molecules from bonding together at their normal freezing point of 0℃ or 32℉. The addition of salt actually lowers the freezing point of water! 

When this occurs, we can’t actually see the sodium and chlorine ions at work, as they are way too small for our eyes to observe. What we do notice is that, when salt is applied to ice, the ice begins to melt. This is because the composition of water is no longer plain H 2 O; it now has sodium and chlorine ions floating around in it, causing the freezing point to decrease.

How’s that for some snazzy science?

Making the Science of Salt and Water Visible

In order to visualize the concept of salt lowering the freezing point of water, I gathered a few simple supplies from my kitchen and got to work. This experiment took approximately 30 minutes for my kids to complete from start to finish, with additional time to discuss the environmental implications of adding salt to icy roadways.

Materials Needed for the Science Experiment

To demonstrate how salt affects the freezing point of water, you’ll need the following materials:

• 2 Ice cubes
• Table salt*
• Timer or Clock

*You can use either fine or coarse table salt for this experiment. I chose to use both to demonstrate the difference in melting time for each option. If you want to test both salt types as well, you will need 3 ice cubes and 3 bowls.

Make Predictions to Practice Critical Thinking Skills

To engage your learners in critical thinking (and to add an extra layer of fun to the science experiment!) have them make the following predictions prior to conducting the experiment:

• Which ice cube will melt the fastest?
• How much time will it take for the plain ice cube to melt?
• How much time will it take for the salty ice cube to melt?

Not only do these questions get students thinking about the experiment, but they also allow them to make mathematical comparisons to the results, engaging the “M” in STEM! Have your learners record their predictions in a table, like the one shown below. 

Title: What Effect Does Salt Have on Ice?

I’ll explain more about teaching students how to collect data in an organized manner in the data collection portion of this post.

Most importantly, this is a fun activity to get your kids thinking and making hypotheses. Most children are afraid of being “wrong”; this activity teaches them that being wrong is part of the fun! Taking educated guesses is what drives science forward because when we realize our answer is wrong, we can confidently move forward in the right direction! Try to foster the idea that it’s not the “right” or “wrong” answer that’s important, but rather the learning that happens as a result of the experiment.

Instructions to Conduct the Salty Ice Experiment

Follow these step-by-step instructions to visualize the effect salt has on the ice.

• Set the bowls on a level surface.
• Place an ice cube in each bowl.
• Label the first bowl as your control. This bowl will only contain an ice cube.
• Label the second bowl as your variable. 
• Into the second bowl, pour one teaspoon of table salt on top of the ice cube.
• Record the time or start a stopwatch
• Observe the difference in the time it takes for the two ice cubes to melt.

If you have chosen to test the effect that both fine and coarse table salt have on the ice cubes, add a step to the instructions, applying one teaspoon of the additional salt to a third ice cube.

The temperature of the surrounding air will affect the rate at which both ice cubes melt. You want to specifically focus on the difference in time between the melting rates of the ice cubes.

Simple Data Collection for the Science Experiment

This is a great activity to introduce or reinforce the importance of recording data in an organized manner. Create a simple table like the one below for your learners to write down their observations. Point out that a table must have a title, clear labels explaining what each value represents, along with the units of measurement used.

Here is an example of a table to use for the salty ice experiment:

If you have chosen to test an additional type of table salt, be sure to add an extra column to the table.

Discussion Questions for the Salty Ice Experiment

Once your learners have completed the salty ice science experiment, have them revisit their predictions and compare them to the results. Try to avoid statements such as, “Were your predictions right or wrong?” as the aim is not for them to be accurate in their assumptions, but instead to learn how to properly conduct an experiment and analyze results. Here are some prompts you can try to get them thinking:

• Which ice cube changed from solid to liquid first? Why do you think that happened?
• How does the melting time of the plain ice cube compare to your prediction? Did it melt faster or slower than you predicted?
• How does the melting time of the salted ice cube compare to your prediction? Did it melt faster or slower than you predicted?
• How can this knowledge be useful to someone that lives in a climate zone that receives ice and snow in the winter?

Depending on the age and ability level of your learners, have them calculate the numerical difference in predicted versus actual melting times of each ice cube to add an extra mathematical component to this lesson.

Environmental Implications of Using Salt to Decrease Ice Accumulation on Outdoor Surfaces

To apply what they have learned, introduce and discuss the environmental issues that arise when salt is applied in abundance to icy roadways and outdoor surfaces. You can utilize the video lesson I created with Medinah Eatman of Science Teacher Mom to guide this portion of their learning, beginning at the Nature Connection section, found at minute 15 of the virtual lesson. You’ll notice that I reference a printable in the video, which you can access for free here:

Here are the main takeaways from this section of the lesson:

• Excess salt washes into local waterways, causing problems for the plants and animals that reside there.
• Fresh water fish that reside in local waterways have hatchlings that are 30% smaller than average when exposed to higher salinity. Salinity is a value that addresses the amount of salt dissolved in water. 
• Increased salinity in freshwater can kill zooplankton and phytoplankton, which are important food resources for fish, clams, snails, and insects.
• Plants can be negatively affected by increased salinity, causing them to have smaller leaves, flowers, and fruit, as well as slower stem growth.
• Large mammals like deer and moose are attracted to the salted roadways, causing in increase in collision rate with these animals during winter months.

The lesson then goes on to discuss the appropriate level of salt to use per area of ice, as well as some salt alternatives currently available to treat icy surface conditions.

Making Science Easily Accessible

Conducting simple scientific experiments like this one allows students to see that science is everywhere and doesn’t require fancy equipment to conduct investigations. Additionally, their confidence in making predictions and interpreting information will grow, strengthening their critical thinking skills.

If you try this salted ice experiment, please let me know by tagging me @thoughtfullysustainable on Instagram or Facebook , or by leaving a comment below! If you have any questions, feel free to email me!  

Instructions

1. Set the bowls on a level surface. 2. Place an ice cube in each bowl. 3. Label the first bowl as your control. This bowl will only contain an ice cube. 4. Label the second bowl as your variable. 5. Into the second bowl, pour one teaspoon of table salt on top of the ice cube. 6. Record the time or start a stopwatch 7. Observe the difference in the time it takes for the two ice cubes to melt.

You can use either fine or coarse table salt for this experiment. I chose to use both to demonstrate the difference in melting time for each option. If you want to test both salt types as well, you will need 3 ice cubes and 3 bowls.

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• Melting Ice Experiment

Melting ice experiment – 15-minute festive STEM activity

STEM , Science

How can we make ice melt more easily? Find out with this festive melting ice experiment from the  15-Minute STEM series by Emily Hunt…

• Red and green ice cubes (add food colouring to water and freeze in ice cube trays)
• Bowl of cold water

Melting ice experiment learning objective

Salt lowers the freezing point of water, helping to melt ice faster. In this melting ice experiment, as each ice cube melts the string sinks into it. Meanwhile the cold water in the bowl dilutes the salt/water mixture, allowing the top of each ice cube to refreeze, trapping the string inside it.

In the winter in the UK, road gritters use rock salt to prevent the roads from getting too icy. The salt is spread onto the road surface before temperatures drop below freezing (0 degrees Celsius) to reduce the risk of ice forming on the ground.

Curriculum links

• Year 4 (States of Matter)
• Year 5 (Properties and Changes of Materials)

Emily Hunt is an experienced primary school teacher with a passion for promoting STEM education. She regularly writes articles and speaks about STEM, and shares activities and blogs on her  website . Emily holds a Masters of Education from the University of Cambridge and has also worked within the US education system to deliver science outreach.

Download another ice-themed lesson plan .

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• Pasta skeleton – 15-minute STEM activity for Halloween
• Little Inventors – KS2 STEM inventions resource pack
• Space activities for kids – Active learning Planet Match game
• Wind speed measurement – Make an anemometer with paper cups

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Science for Kids: Salt and Ice Experiments

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Brrr! Winter brings ice and snow and all the fun and not-so-fun activities along with it. As you or your children may end up shoveling a walkway or driving behind a snow plow this winter, everyone might be wondering why we use salt to help melt ice on our walkways and roads. Here is an easy experiment that is relatable to real-world winter conditions. You can test and observe the effects of salt and other household materials on ice. I’ve included the science and real-world applications at the end of this post so you can relate what you discover to the conditions you’ve experienced this winter!

Materials for Salt and Ice Science Experiment

You most likely have everything you need for this experiment right in your kitchen. There is a lot of wiggle room in your experimental design. Have your children help decide what materials you will test on the ice.

You will need:

• Kitchen scale (these scales are great for tons of different science experiments )
• At least one of the following: sea salt, kosher salt, or other salts from around the globe (try these fun salts for some variety !) sugar, cornstarch, coffee, sand, baking soda, cornmeal, bath salts, etc.
• Several containers or small plates
• Stopwatch or clock
• Measuring spoons

The beauty of this experiment is that you can test just about anything on your ice cube. Just stick to harmless household items. Skip powdered soaps or caustic materials that might be irritating to eyes and skin.

Salt and Ice Experiment

Choose your materials and get started. You’ll need at least 3 different containers. One will hold a plain ice cube as the control in the experiment. Another will hold an ice cube and a pre-determined amount of salt, the third will hold an ice cube and a material for comparison. You can certainly set up more than three if you’d like.

For even more accuracy, you can use the kitchen scale to determine the mass of the ice cubes before you begin. Later on, you can mass them again to get an idea of how much water has melted.

Once you’ve done any sort of weighing or measuring the ice cubes and taken notes, put them in the designated containers. Keep one ice cube bare and cover one with salt. Use the same measurement for all of your materials. For example, if you use 1 teaspoon of salt, use 1 teaspoon of sugar on the next cube. Your ice cubes most likely are not all the same size, but you can control the amount of “melter” you are using. It is always good to teach and remind about precision in an experiment.

Once the experiment is set up, wait a designated amount of time (5 minutes is a good place to start) to see the effects. Take notes on observable changes. If you got the mass of the ice before the experiment, you can brush off any salt or other melting agent and weigh the cube again. Note that any particle left on the ice cube does add mass, so this measurement helps with accuracy but is not 100% precise.

Keep track of the changes and determine the results of the experiment. If you are working on graphing in math, this is a great opportunity to graph the masses you observed before and after the experiment.

Why Does Salt Melt Ice?

So why do we use salt on our roads and walkways? Why does it seem to melt ice? Salt lowers the freezing point of water. This is called “freezing point depression”, and it means that the water will not freeze until it has reached a lower temperature than the normal freezing temperature of 32 degrees Fahrenheit (0 degrees Celsius). The salt’s structure makes it more difficult for the water molecules to form the rigid formation they need to be in to become ice.

All substances have freezing points–the temperature at which they freeze–and melting points.  To further explore melting points, check out  science experiment with the pop-up timers used to cook meat .

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Ice and Salt Experiment for Preschool

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