Hot+Ice

= Hot Ice = by Chris Fennig and Ben Gambler This lesson is appropriate for grades 6-8 with a focus on solubility, supersaturation, enthalpy, ionic solutions, and commercial uses.
 * Grade Level and Topic **

This lesson fits the PA Science Standards 3.4.7 A, "Describe concepts about the structure and properties of matter" and B, "Relate energy sources and transfers to heat and temperature." It fits the National Science Education Standards of grades 5-8 of "properties and changes of properties in matter" and "transfer of energy." Hot ice is a demonstration in which a supersaturated solution of sodium acetate is disturbed, causing crystallization and the release of heat. The solution consists of sodium acetate dissolved in hot water that was subsequently cooled. Ions result when a compound, a material of two or more elements (one a metal and one a nonmetal), dissolves in water. Crystallization/precipitation is the reverse process of dissolving in water. Solubility is how much of a compound can dissolve in water. When the temperature is increased, more compound can dissolve in the water. Some compounds can cause supersaturation in a solution, where more compound dissolves in the solvent than should. The solution resists crystallization until a seed crystal or other disturbance causes crystal formation. As crystals form, bonds are also being formed, which release energy, causing an increase in heat. Thus, you get 'hot ice'.
 * NSES and PA Standards **
 * Objectives **
 * 1) Students will be able to define supersaturation.
 * 2) Students will be able to explain why reactions are endothermic or exothermic.
 * 3) Students will be able to provide examples of at least one consumer item utilizing supersaturation.
 * Content Explanation: **
 * Administrative Considerations **
 * SAFETY: **Risk of being burnt by a hot plate or hot glassware. Use caution around the entire set-up. Handle the beaker with care as it will be hot upon removal from the hot plate. Any broken glassware will be reported to the teacher immediately. Students are**NOT** to drink any of the solutions present. Goggles will be worn at all times.
 * Materials, Equipment, Set-Up **
 * Sodium Acetate (solid, anhydrous)
 * <span style="font-family: 'Times New Roman',serif; font-size: 12pt;">(1) Hot plates
 * <span style="font-family: 'Times New Roman',serif; font-size: 12pt;">(4) Beakers (1 500 mL and 3 250 mL)
 * <span style="font-family: 'Times New Roman',serif; font-size: 12pt;">(2) Glass tray/dish
 * <span style="font-family: 'Times New Roman',serif; font-size: 12pt;">(1) Temperature Probes
 * <span style="font-family: 'Times New Roman',serif; font-size: 12pt;">(1) Computers (with Inspiration program)
 * <span style="font-family: 'Times New Roman',serif; font-size: 12pt;">(4) Goggles
 * <span style="font-family: 'Times New Roman',serif; font-size: 12pt;">Refrigerator
 * <span style="font-family: 'Times New Roman',serif; font-size: 12pt;">(1) Hot pack


 * <span style="font-family: 'Times New Roman',serif; font-size: 12pt;">Procedure: **
 * 1) <span style="font-family: 'Times New Roman',serif; font-size: 12pt;">Place a beaker on the hot plate filled with 400 mL of water. Heat the water to just below boiling. Add enough sodium acetate (at least 304 g) to saturate the solution (until no more dissolves in hot water).
 * 2) <span style="font-family: 'Times New Roman',serif; font-size: 12pt;">Once sodium acetate is dissolved (as much as possible), decant the solution into the other three beakers (100 mL per). Be careful not to disturb the solution too much.
 * 3) <span style="font-family: 'Times New Roman',serif; font-size: 12pt;">Place the beakers out to cool to room temperature. Once cool, move the beakers to the fridge for further cooling (get near 0°C) (careful as any dust or bump could cause premature crystallization).
 * 4) <span style="font-family: 'Times New Roman',serif; font-size: 12pt;">Once completely cooled, the solution is ready to pour at any time (careful transporting). Slowly pour the solution into the glass tray (could crystallize upon pouring or not). If the solution does not crystallize, add a seed crystal or tap the solution with your finger.
 * 5) <span style="font-family: 'Times New Roman',serif; font-size: 12pt;">In a second demonstration, pour the solution into another glass tray. Insert a temperature probe into the solution to induce crystallization. Allow students to observe as the temperature increases.
 * <span style="font-family: 'Times New Roman',serif; font-size: 12pt;">Body of Lesson **
 * 1) <span style="font-family: TimesNewRoman,serif; font-size: 12pt;">Predict (6 min): Concepts such as ionic compounds and solubility will be initially introduced. Then the instructor shows the students a tray of what appears to be water. He explains that the water has a chemical compound called sodium acetate dissolved in it. He tells the students that he will touch the surface of the solution with his finger. He tells the students to predict what will happen, prior to the demonstration. If possible, he encourages students to argue (scientifically, not "You're wrong because I said so!") about their predictions and see if they come to a consensus. (Some students will probably predict that the finger will displace an equal volume of solution).


 * 1) <span style="font-family: TimesNewRoman,serif; font-size: 12pt;">Observe (4 min): The instructor makes sure that all the students are viewing the sodium acetate solution tray and touches the surface of the solution with his finger. If all goes according to plan, the solution will become a solid within seconds. The instructor tells the students to feel the air immediately surrounding the tray, which should be noticeably hotter than the ambient temperature. In the second part of the lesson, students will observe the increase in temperature of the solidified sodium acetate with a temperature probe. If time and resources permit, the instructor may ask a student to touch another tray to show that the process occurs, regardless of who touches the solution or which solution they touch.


 * 1) <span style="font-family: TimesNewRoman,serif; font-size: 12pt;">Explain (10 min): The instructor asks the students to explain, in their own words, what happened when he touched the solution. If the students need hints, the instructor may tell them to think of salt dissolving in water. What happens if you add too much salt? The solution is supersaturated, or has more compound dissolved in water than normally possible. The introduction of a spot to form crystals results in the rapid precipitation of the solid. The instructor will also have students explain what caused the heat when the solution crystallized. If the students need hints, the instructor may tell them to think about the process of using a hot pack. Breaking the ionic bonds to dissolve sodium acetate is an endothermic process, which is why the solution was heated prior to demonstration and also why one heats a hot pack, usually in the microwave, before using. Touching the sodium acetate causes the ionic bonds to form again and make a solid, which is an exothermic process. The exothermic process releases heat to its surroundings, which is why the air around the solution was hotter and why a hot pack works as intended.


 * <span style="font-family: 'Times New Roman',serif; font-size: 12pt;">References: **
 * 1) <span style="font-family: 'Times New Roman',serif; font-size: 12pt;">Helmenstine, A. M. "Hot Ice or Sodium Acetate." About.com - Chemistry. http://chemistry.about.com/od/homeexperiments/a/make-hot-ice-sodium-acetate.htm
 * 2) //<span style="font-family: 'Times New Roman',serif; font-size: 12pt;">HOT ICE (science fair winner). //<span style="font-family: 'Times New Roman',serif; font-size: 12pt;"> Kid Science. http://www.columbiascientific.com/science-fair-experiments/hot-ice-science-fair-winner
 * 3) <span style="font-family: 'Times New Roman',serif; font-size: 12pt;">Jacobsen, J. J.; Moore, J. W. "Crystallization of Saturated Sodium Acetate." Chemistry Comes Alive! Volume 3 //J. Chem. Educ. Software// **SP23**
 * 4) <span style="font-family: 'Times New Roman',serif; font-size: 12pt;">Lewis, Brian. "An Explanation of Sodium Acetate & Hot Ice." Livestrong.com. http://www.livestrong.com/article/251878-an-explanation-of-sodium-acetate-hot-ice/