16.3 lesson 16.3 colligative properties of...
TRANSCRIPT
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16.3
Lesson 16.3 Colligative Properties of Solutions
Objectives
● 16.3.1 Explain how colligative properties can beexplained on a particle basis.
Lesson Links
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Overview/Materials
Overview
In this lesson, you will cover the topic of colligative properties ofsolutions.
Classroom Materials
Describing Colligative Properties: thermometer, foam cup, rock salt,water, ice
Pacing
Standard
1
Block
0.5
Standard
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Chemistry & You
Description
Engage
Instruct students to read the Chemistry &You feature on p. 534.
Ask What do you think would happen if youforgot to add rock salt to the ice in an icecream machine? (The ice cream mixturewould not get cold enough to freeze.)
Ask What do you think would happen if youadded too much salt to the ice in an icecream machine? (The ice cream mixturecould freeze too quickly, making the textureof the resulting ice cream hard orcrystallized.)
Resources
Content Chapter 16 Online StudentEdition
Pacing
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Activate Prior Knowledge
Description
Engage
Have students write the chemical equationsfor the following examples to refresh theirunderstanding of aqueous solutions.
• hydrochloric acid in water (HCl(g)→ H+(aq) +Cl-(aq))
• magnesium chloride in water (MgCl2(s)→ Mg2+(aq) + 2Cl-(aq))
• glucose in water (C6H12O6(s)→C6H12O6(aq))
Resources Pacing
Describing Colligative Properties
Description
Explain
Remind the students that the properties ofsolutions differ from those of the puresolvent. Explain that some of the changesin properties only depend on there beingsolute particles in solution, not on thespecific type of solute particles.
Remind students that ionic compounds andcertain molecular compounds, such as HCl,produce two or more particles when theydissolve in water. Most molecularcompounds, such as glucose, do notdissociate when they dissolve in water. Foreach formula unit of MgCl2 that dissolves,three particles are formed in solution.
Ask How many particles are formed when FeCl3 dissolves in water? (4)
Direct students to Figure 16.12 (Figure16.12_part1, Figure 16.12_part2, Figure 16.12_part3, Figure 16.12_part4).Emphasize that colligative properties do notdepend on the type of particles; rather,they depend on the concentration. Forcolligative properties, a mole of one kind ofparticle has the same effect as a mole ofany other kind of particle.
Ask Which produces a greater change incolligative properties—an ionic solid or amolecular solid? (An ionic solid produces agreater change because it will produce twoor more moles of ions for every mole ofsolid that dissolves.)
Resources
Content Figure 16.12, part 1
Content Figure 16.12, part 2
Content Figure 16.12, part 3
Content Figure 16.12, part 4
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Describe the colligative properties of vapor-pressure lowering, freezing-pointdepression, and boiling-point elevation.
Describing Colligative Properties
Description
Explore
Have students make an ice-water slurry intheir cups. Ask them to measure the initialtemperature of the ice-water slurry and thelowest temperature reached after theaddition of the rock salt. Explain that theobserved difference in temperature is thefreezing-point depression for this solution ofNaCl in water.
Materials: thermometer, foam cup, rock salt,water, ice
Resources Pacing
Describing Colligative Properties
Description
Extend
Show Figure 16.13_part1 and Figure 16.13_part2 and have students investigatedifferent compounds used for de-icing.Have students determine the chemicalformula for each de-icer and if they aremolecular or ionic compounds. Also askthem to research the maximum freezing-point depression and the advantages anddisadvantages of each.
Have pairs work through the Ch. 16Concepts in Action: Sorbet Solutions on PearsonChem.com to further visualize thefreezing-point depression applications.
Resources
Content Figure 16.13, part 1
Content Figure 16.13, part 2
Content Ch. 16 Concepts in Action:Sorbet Solutions
Pacing
Describing Colligative Properties
Description
Explain
Ask a student volunteer to explain how a car's cooling system works. Include visuals iftime allows. Lead a discussion comparingthe consequences of cooling a car engine
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with pure water to those of using antifreezein the cooling system. Point out that, whenwater freezes, it must form a crystallinelattice. Encourage students to think aboutwhat effect adding a solute has on the abilityof water to form that lattice readily at normalfreezing temperatures.
Assess and Remediate
Description
Evaluate
Have students explain, using words ordiagrams, how the addition of soluteparticles to a solvent causes the vaporpressure and freezing point of the solution todecrease relative to the pure solvent and theboiling point to increase.
Then, have the students complete the 16.3Lesson Check.
Remediate
Guide students to understand that colligativeproperties are those physical properties ofsolutions that depend only on the number ofparticles of solute in solution and not on thechemical composition of the particles.Explain that the magnitudes of the observedphysical changes are proportional to thequantity of solute particles in solution.
Resources
Content Chapter 16 Online StudentEdition
Pacing
Differentiated Instruction
Description
Special Needs Students
Have students share their experiences withantifreeze, car de-icers, and road brinetreatments. Tell students that each of theseproducts work because of their colligativeproperties in solution.
Advanced Students
Have students use phase diagrams to helpillustrate the effects of solutes on vaporpressure, boiling point, and freezing pointof a solution. Also have students investigatethe Ch. 16 Directed Virtual Lab: Solutionson PearsonChem.com to quantify theextent of the effect solutes can have onfreezing-point depression and boiling-pointelevation of solutions.
Resources
Content Ch. 16 Directed Virtual Lab:Solutions
Content 16.3 Kinetic Art: VaporPressure
Content Study WB Chapter 16Lesson 3
Content Ch. 16 Core TR: Section3 Review
Pacing
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Struggling Students
Have students watch the 16.3 Kinetic Art:Vapor Pressure animation on PearsonChem.com and discuss theaccompanying questions in groups tounderstand the property of vapor-pressurelowering.
Focus on ELL
Description
Content and Language
Write the words property, depression, and elevation on the board. Explain that thesethree words have both common andscientific meanings. Divide the class intothree groups, and assign one word to eachgroup. Have groups look up the definitionsfor their word, then explain the similaritiesand differences between the common andscientific meanings to the rest of the class.
Resources
Content Study WB Chapter 16Lesson 3
Content Ch. 16 Core TR: Section3 Review
Pacing
My Notes
Homework