Lecture Free Teaching: Properties of Solutions
2010 KSTA ConferenceLisa DevillezMarshall County High School
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!
Lecture Free Teaching (LFT)
• Clear and concise objectives– Notes– Homework– Tests
• Mastery learning & standards-based grading are complementary LFT
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
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
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.
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
The Labs: Documentation
• Data Tables• Standards graphs
– Trend line– Correlation value (R2)
• Calculations– Verification of student solution concentration– % error
Glucose Standards
Grams in 500ml H2O
Density(18.3ᵒC)
%w/w Molality(mol/kg)
Molarity(mol/L)
26.3 1.015 5 0.292 0.282
55.56 1.040 10 0.617 0.641
125 1.075 20 1.39 1.492
214.29 1.110 30 2.38 2.640
333.33 1.155 40 3.70 4.126
Glucose Standards
Grams in 500ml H2O
ppm
0.15 300
0.25 500
0.35 700
0.45 900
0.55 1100
Hydrometry : Specific gravity
Refractometry: Snell’s Law
“The determination of the concentrations of sugar solutions by Laser Refractometry” Hughes & JelksJCE November 1988
Refractometry: Snell’s Law
Colligative Properties: Freezing point
• Assigned 2.0M 100mL• Standards in molalities
Spectroscopy: Beer’s Law
• 5mL glucose solution & 5mL Benedict’s• Spec 20; 730nm; distilled water blank
Calibration Curves
0 5 10 15 20 25 30 35 40 450
0.25
0.5
0.75
1
1.25
1.5
1.75
2
2.25
2.5
2.75
3
3.25
3.5
3.75
4
4.25
4.5
4.75
f(x) = 0.109268292682927 x − 0.0146341463414634R² = 0.996178166909874
Refractometry
w/w %
Disp
lacm
ent
Calibration Curves
0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.25 2.5 2.750.95
0.975
1
1.025
1.05
1.075
1.1
1.125
1.15
1.175
f(x) = 0.0536440111648864 x + 1.00584436219856R² = 0.966101076963197
Hydrometry
Molarity
Spec
. Gra
vity