The melt Point
In this 15-minute companion task to That"s a (N)ice Temperature!, teams of children ages 8 come 13 predict which ice cream cube will melt faster, one sprinkled v salt, or one there is no salt. After making their predictions, the youngsters pour salt on one ice cream cube and also leave the other untouched, then observe for two minutes to see if their predictions to be correct. Kids learn that adding salt — or various other substances — to ice cream lowers the melting point of ice. Finally, they placed their knowledge to the check by making ice cream!
What"s the Point?Water can exist in different states; ice is the hard state the water. The melting suggest of pure water ice cream is 32°F (0°C). adding salt — or various other substances — to ice lowers the melting point of ice.
For each childHis/her Ice Investigator Journal 1 pencil or pen 1 (1-quart) Ziploc baggie 1 (1-gallon) Ziploc baggie 1 tablespoon sugar 1/2 cup milk 1/4 teaspoon vanilla 2 tablespoons absent salt sufficient ice cubes to nearly fill the gallon baggie 1 plastic spoon
For each team of 4 to 6 children:1 Styrofoam key 2 ice cream cubes 1/4 teaspoon of salt small cup because that the salt file towel Magnifying glass (optional)
For the facilitator:
PreparationPre-measure the salt and place in small cups think about pre–mixing the ice cream ingredient
ActivityAsk the youngsters to guess what will occur when salt is sprinkled ~ above an ice cube. Have castle annotate their predictions in their Ice Investigator Journal. Divide the children into groups of 4 to six and invite them to do an experiment that will test your predictions! Distribute the materials, including the plate, salt, two ice cubes, and also magnifying glass to every team. Let the melt begin! Invite the youngsters to sprinkle salt on top of one of their ice cream cubes, being mindful not to get any type of salt on the 2nd cube. Have actually them observe their cubes for around two minutes and also record your findings in your Ice Investigator Journals.
Facilitator"s Note: transforms in temperature can reason water to adjust state, and these transforms occur at certain temperatures. Fresh water transitions between the solid and also liquid says at 32°F (0°C) in ~ sea level. Pure water ice cream melts and changes state indigenous a solid come a fluid (water) in ~ temperatures below this melting point.
After the youngsters have made and also recorded their observations in their Ice Investigator Journals, encourage them to attract conclusions about what castle observed.
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What occurred to the ice cube as soon as salt to be poured ~ above it? It began to melt. Both ice cream cubes started at the very same temperature. Why walk one melt much faster than the other? The salt led to the ice cream to melt faster. Share with the children that adding salt lowers the temperature at which water freezes. Freshwater freezes in ~ 32°F (0°C), yet the freezing suggest of seawater is lower: about 28°F (-2° C). The saltier the water is, the cooler it needs to be come freeze.
Facilitator"s Note: The better the amount of salt, the lower the freezing allude (to a point; when there is sufficient salt the no more will dissolve, the freezing point no much longer decreases). Ocean water is around 3.5% salt; sea water freezes at around 28°F (-2° C). A 10% salt equipment freezes at around 20°F (-6°C), and a 20% solution freezes in ~ 2°F (-16°C).
can they think of any kind of connection this can have to their lives? One important connection for kids who live in cooler climates is the use of salt — or various other substances — on frozen roads. Why would salt be poured onto roads that were covered in ice? When you to water salt top top frozen roads the salt dissolves into the liquid water in the ice and also lowers its freezing point, so the the temperatures have actually to get even cooler to make the salty water freeze. Salted roads stay ice-free also at temperatures as cold as 15°F (-9°C). Other chemicals, such together calcium magnesium acetate, likewise are provided to melt ice cream on roads. Lock are less harmful come the atmosphere than absent salt (sodium chloride).
Facilitator"s Note: once salt is added to one icy road, the salt starts to dissolve as it comes into contact with the ice; this renders salt water v a very high concentration of salt! The braided water proceeds to connect with the ice, lowering that freezing allude and melting it. The temperature would have to drop listed below the freezing allude of pure water (32°F, 0°C) in order to freeze the braided water. Plenty of different salt are offered for deicing roads. Salt chloride (NaCl) is a typical road salt — table salt is a greater grade of sodium chloride. At colder temperatures, salts favor magnesium chloride or calcium chloride are regularly used because they alleviate the melting point even further.
have actually the youngsters ever made home-made ice cream cream? just how is salt used? Salt and ice are placed in an outer bucket. An inner container the holds the ingredient for ice cream cream is put in this salty ice. Why would certainly salt be supplied to aid make ice cream cream? Salt permits the temperature of the ice water roughly the ice cream container come drop listed below the melting point of pure water; it provides it cooler than simply plain ice and also freezes the ice cream.
Facilitator"s Note: Pure water and also ice, maintained insulated from the warm outside world, pertained to equilibrium over time. On a molecule level, water molecules room freezing onto the ice at the same rate as they room melting off of it. The entire water/ice solution is in ~ the melting/freezing point, 32°F (0°C). Adding rock salt — or any type of substance that dissolves in water — disrupts this equilibrium. Under water molecule are connecting with the ice cream at any given moment, so the freezing rate is slowed. The salt has no impact on the melting rate, so an ext melting occurs than freezing — melt "wins" — and the ice melts. In law so, heat power is used to rest the hydrogen bond that host the molecule in the ice cream together. In various other words, the ice "uses up" part warmth indigenous the solution and also the temperature drops. Melting and freezing again match rates ("tie") again as soon as the temperature has dropped to the new melting point.
Invite the children to put their new-found understanding to the test together they do ice cream in a baggie! Provide each boy with a quart-sized Ziploc baggie and also the sugar, milk, and vanilla. Have actually them to water the ingredients into the baggie, seal the baggie, and also mix castle up. Have them fill a gallon-sized Ziploc baggie with enough ice cubes to almost fill the bag, 2 tablespoons of absent salt, and also the smaller baggie — well sealed! — with the ingredients. Invite the children to shake and roll the bag approximately until the inside ingredients are frozen (about 20 minutes). While anyone enjoys your treats, review what the youngsters learned about how including salt — or other substances — lowers the melting suggest of water.
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If the kids have started to build a snow mobile, invite them come record any type of answers they uncovered on the appropriate pieces.