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Lecture Free Teaching: Properties of Solutions 2010 KSTA Conference Lisa Devillez Marshall County High School

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Lecture Free Teaching (LFT) Note-making as “homework” / Vodcasting foundational lectures – improves textbook reading skills – classroom discussion focused on student questions – more class time for labs – more time for "advanced" problems Active Learning!

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Lecture Free Teaching (LFT) Clear and concise objectives – Notes – Homework – Tests Mastery learning & standards-based grading are complementary LFT

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Lecture Free Teaching (LFT) Class time – Opportunity for student feedback – Collection of active learning activities – Limit “lectures” (ie., passive instruction) in both frequency and time

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Solutions The perfect “unit” for LFT and developing lab skills Narrowed scope of objectives based on difficulties of former students Selected / modified labs to address all of the objectives

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Objectives 5.1 Define units of concentration, mass percent, ppm, mole fraction, molarity, and molality, and be able to calculate each from appropriate data. 5.2 Be able to convert a concentration from one unit to the other. 5.3 Be able to calculate solution concentration for single and serial dilutions. 5.4 Describe the effect of solute (or solvent) concentration on boiling point and freezing point. Be able to calculate any of these effects from concentration data for nonelectrolyte solutes.

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The Labs: General Format Prepare a solution of the assigned concentration. Measure property for 5 standard solutions (teacher- prepared) and student solution. Graph property vs. concentration for the standards Use equation for trend line and measurement for student solution to verify its concentration

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The Labs: Documentation Data Tables Standards graphs – Trend line – Correlation value (R 2 ) Calculations – Verification of student solution concentration – % error

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Glucose Standards Grams in 500ml H 2 O Density (18.3ᵒC) %w/wMolality (mol/kg) Molarity (mol/L) 26.31.01550.2920.282 55.561.040100.6170.641 1251.075201.391.492 214.291.110302.382.640 333.331.155403.704.126

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Glucose Standards Grams in 500ml H 2 O ppm 0.15300 0.25500 0.35700 0.45900 0.551100

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Hydrometry : Specific gravity

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Refractometry: Snell’s Law “The determination of the concentrations of sugar solutions by Laser Refractometry” Hughes & Jelks JCE November 1988

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Refractometry: Snell’s Law

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Colligative Properties: Freezing point Assigned 2.0M 100mL Standards in molalities

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Spectroscopy: Beer’s Law 5mL glucose solution & 5mL Benedict’s Spec 20; 730nm; distilled water blank

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Calibration Curves

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Molarity and Molality.

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