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