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Chemical Principles Visualized: Lecture demonstrations and activities David A. Katz Chemist, educator, and consultant Tucson, AZ 85745, USA Voice: 1-520-624-2207 Email: [email protected] Web site: www.chymist.com

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Page 1: Chemical Principles Visualized 23ICCE Toronto Principles Visualized 23ICCE.pdfChemical Principles Visualized: Lecture demonstrations and activities David A. Katz Chemist, educator,

Chemical Principles Visualized:

Lecture demonstrationsand activities

David A. KatzChemist, educator, and consultant

Tucson, AZ 85745, USAVoice: 1-520-624-2207

Email: [email protected] site: www.chymist.com

Page 2: Chemical Principles Visualized 23ICCE Toronto Principles Visualized 23ICCE.pdfChemical Principles Visualized: Lecture demonstrations and activities David A. Katz Chemist, educator,

Chemistry is Fun!• Chemistry, as an experimental science, is not just an intellectual pursuit, but, a hands‐on (or “hands‐in”) science.  

• Through chemistry we can create a wondrous range of substances and materials with unique colors, odors, and properties.  

• None of the physical or natural sciences are as creative as chemistry.

Page 3: Chemical Principles Visualized 23ICCE Toronto Principles Visualized 23ICCE.pdfChemical Principles Visualized: Lecture demonstrations and activities David A. Katz Chemist, educator,

• Students, on the average, have little or no concrete concepts or experiences of the phenomena described in a chemistry course.

• Typical instructors just talk about chemistry and chemical reactions.

• Students cannot think in 3‐D.• Students have limited visualization skills– Pictures may help– Videos are better– Live demonstrations and hands‐on activities in the classroom enhance the learning of concepts.  

Page 4: Chemical Principles Visualized 23ICCE Toronto Principles Visualized 23ICCE.pdfChemical Principles Visualized: Lecture demonstrations and activities David A. Katz Chemist, educator,

Molecular ShapesUsing Modeling Clay and Toothpicks

• The shape of a molecule plays an important role in its reactivity.

• Students cannot think in 3‐D

•Manipulating “atoms” into molecular shapes formalizes VSEPR

• Teach shapes BEFORE Lewis dot structures

Page 5: Chemical Principles Visualized 23ICCE Toronto Principles Visualized 23ICCE.pdfChemical Principles Visualized: Lecture demonstrations and activities David A. Katz Chemist, educator,

Molecular ShapesModeling clay and toothpicks to build shapes

MX2 – linear, 180° bond angle Characteristic of Periodic Table Group IIA

Page 6: Chemical Principles Visualized 23ICCE Toronto Principles Visualized 23ICCE.pdfChemical Principles Visualized: Lecture demonstrations and activities David A. Katz Chemist, educator,

Molecular Shapes

MX3triangular planar (trigonal planar)120° bond angle

Characteristic of Periodic Table Group IIIA

Page 7: Chemical Principles Visualized 23ICCE Toronto Principles Visualized 23ICCE.pdfChemical Principles Visualized: Lecture demonstrations and activities David A. Katz Chemist, educator,

Molecular Shapes

MX4tetrahedral

109.5° bond angleCharacteristic of Periodic Table Group IVAStudents must physically form a 3-D structure

Page 8: Chemical Principles Visualized 23ICCE Toronto Principles Visualized 23ICCE.pdfChemical Principles Visualized: Lecture demonstrations and activities David A. Katz Chemist, educator,

Molecular ShapesMolecules with non‐bonded electron pairs

Trigonal pyramid107.5° bond angle

Characteristic of Periodic Table Group VA

Bent104.5° bond angle

Characteristic of Periodic Table Group VIA

Page 9: Chemical Principles Visualized 23ICCE Toronto Principles Visualized 23ICCE.pdfChemical Principles Visualized: Lecture demonstrations and activities David A. Katz Chemist, educator,

Visual Stoichiometry

CH4 +         O2 CO2 +     H2O  (equation not balanced)

Page 10: Chemical Principles Visualized 23ICCE Toronto Principles Visualized 23ICCE.pdfChemical Principles Visualized: Lecture demonstrations and activities David A. Katz Chemist, educator,

Visual Stoichiometry

H2SO4 +  2 NaOH   Na2SO4 +  2 H2O

Page 11: Chemical Principles Visualized 23ICCE Toronto Principles Visualized 23ICCE.pdfChemical Principles Visualized: Lecture demonstrations and activities David A. Katz Chemist, educator,

Density

Indiana Jones – Raiders of the Lost Ark

Page 12: Chemical Principles Visualized 23ICCE Toronto Principles Visualized 23ICCE.pdfChemical Principles Visualized: Lecture demonstrations and activities David A. Katz Chemist, educator,

Coke vs. Diet Coke

Page 13: Chemical Principles Visualized 23ICCE Toronto Principles Visualized 23ICCE.pdfChemical Principles Visualized: Lecture demonstrations and activities David A. Katz Chemist, educator,

Hot and ColdSeparate water by density

COLD                                    HOT

HOT

COLD

Page 14: Chemical Principles Visualized 23ICCE Toronto Principles Visualized 23ICCE.pdfChemical Principles Visualized: Lecture demonstrations and activities David A. Katz Chemist, educator,

Visible LightAn overhead projector spectroscope

Holographic diffraction grating (Flinn C-Spectra)

Slit and colored filters

Page 15: Chemical Principles Visualized 23ICCE Toronto Principles Visualized 23ICCE.pdfChemical Principles Visualized: Lecture demonstrations and activities David A. Katz Chemist, educator,

Visible LightAn overhead projector spectroscope

Holographic diffraction grating

Slit and colored filters

Page 16: Chemical Principles Visualized 23ICCE Toronto Principles Visualized 23ICCE.pdfChemical Principles Visualized: Lecture demonstrations and activities David A. Katz Chemist, educator,

The Electromagnetic Spectrum

Viewing spectra using holographic diffraction grating (Flinn Scientific C‐Spectra)

Hydrogen spectrum Helium spectrum

Page 17: Chemical Principles Visualized 23ICCE Toronto Principles Visualized 23ICCE.pdfChemical Principles Visualized: Lecture demonstrations and activities David A. Katz Chemist, educator,

Colored Flames

Strontium – redLithium ‐ redCalcium – red/orangeCopper – green or blueBarium – yellow‐greenPotassium – violetSodium ‐ yellow

lithium potassium

calcium barium

Page 18: Chemical Principles Visualized 23ICCE Toronto Principles Visualized 23ICCE.pdfChemical Principles Visualized: Lecture demonstrations and activities David A. Katz Chemist, educator,

Optical Rotation• An optically active compound can 

rotate light• Due to an asymmetrical carbon 

atom (carbon bonded to 4 different groups)

• Enantiomers: molecules are mirror images of themselves

• Solutions of the D‐ isomer twists the light clockwise; L‐isomer twists light counter‐clockwise(Note:  A kit is available from Flinn Scientific)

Dextrose (d-glucose)solution in polarized light on an overhead projector

Page 19: Chemical Principles Visualized 23ICCE Toronto Principles Visualized 23ICCE.pdfChemical Principles Visualized: Lecture demonstrations and activities David A. Katz Chemist, educator,

Iodine

Page 20: Chemical Principles Visualized 23ICCE Toronto Principles Visualized 23ICCE.pdfChemical Principles Visualized: Lecture demonstrations and activities David A. Katz Chemist, educator,

1. Intermolecular forces using I2

1. Iodine vapor2. Iodine‐hexane: 

Nonpolar interactions (London forces)

Page 21: Chemical Principles Visualized 23ICCE Toronto Principles Visualized 23ICCE.pdfChemical Principles Visualized: Lecture demonstrations and activities David A. Katz Chemist, educator,

2. Intermolecular forces using I2

Dipole ‐ Induced dipole

Page 22: Chemical Principles Visualized 23ICCE Toronto Principles Visualized 23ICCE.pdfChemical Principles Visualized: Lecture demonstrations and activities David A. Katz Chemist, educator,

3. Intermolecular forces using I2

Ion – induced dipole

Page 23: Chemical Principles Visualized 23ICCE Toronto Principles Visualized 23ICCE.pdfChemical Principles Visualized: Lecture demonstrations and activities David A. Katz Chemist, educator,

4. Intermolecular forces using I2

Solubility preference:Like dissolves like Hexane 

layer

Water layer

Page 24: Chemical Principles Visualized 23ICCE Toronto Principles Visualized 23ICCE.pdfChemical Principles Visualized: Lecture demonstrations and activities David A. Katz Chemist, educator,

Intermolecular forces:Salting Effects 

Mixture of 2‐propanol and water    (15 mL of each)Add food colorAdd 7 g ammonium sulfate and shakeTest layers for conductivity

Reference:  J. Chem. Educ, 87, 1332 (December 2010)

Page 25: Chemical Principles Visualized 23ICCE Toronto Principles Visualized 23ICCE.pdfChemical Principles Visualized: Lecture demonstrations and activities David A. Katz Chemist, educator,

Intermolecular forces Drops of water on a coin

How many drops of water can you put on a coin?  Why?

Page 26: Chemical Principles Visualized 23ICCE Toronto Principles Visualized 23ICCE.pdfChemical Principles Visualized: Lecture demonstrations and activities David A. Katz Chemist, educator,

Intermolecular forces: Decrease in Volume

ethanol and water

Page 27: Chemical Principles Visualized 23ICCE Toronto Principles Visualized 23ICCE.pdfChemical Principles Visualized: Lecture demonstrations and activities David A. Katz Chemist, educator,

Intermolecular forces: Decrease in Volume

ethanol water

Page 28: Chemical Principles Visualized 23ICCE Toronto Principles Visualized 23ICCE.pdfChemical Principles Visualized: Lecture demonstrations and activities David A. Katz Chemist, educator,

Hydrogen BondingIncrease in Volume

HCl + NaOH NaCl + H2O

Page 29: Chemical Principles Visualized 23ICCE Toronto Principles Visualized 23ICCE.pdfChemical Principles Visualized: Lecture demonstrations and activities David A. Katz Chemist, educator,

Hydrogen BondingIncrease in Volume

Hydrated H3O-

O-O distance 2.59 ÅHydrated OH-

O-O distance 2.50 Å

H2OO-O distance 2.82 Å

Source: Martin Chaplin,http://www1.Isbu.ac.uk/water/index.html

Page 30: Chemical Principles Visualized 23ICCE Toronto Principles Visualized 23ICCE.pdfChemical Principles Visualized: Lecture demonstrations and activities David A. Katz Chemist, educator,

Intermolecular Forces:Which Will Evaporate First?

What factors affect evaporation?Spread these compounds on black chalkboards

Water              methanol             ethanol               2‐propanolEffect of molecular weight:

H2O = 18         CH3OH = 32       C2H5OH = 46           C3H8OH = 60    

Effect of polarity

Page 31: Chemical Principles Visualized 23ICCE Toronto Principles Visualized 23ICCE.pdfChemical Principles Visualized: Lecture demonstrations and activities David A. Katz Chemist, educator,

Acids and Bases

• Svante August Arrhenius (1859 –1927)– Acid produces hydrogen ions in water solution.

• Johannes Nicolaus Brønsted (1879‐1947) and Thomas Martin Lowry (1874‐1936)– An acid‐base reaction consists of the transfer of a proton (or hydrogen ion) from an acid to a base

Page 32: Chemical Principles Visualized 23ICCE Toronto Principles Visualized 23ICCE.pdfChemical Principles Visualized: Lecture demonstrations and activities David A. Katz Chemist, educator,

pH• First introduced by Danish chemist Søren Peder Lauritz 

Sørensen (1868‐1939), the head of the Carlsberg Laboratory’s Chemical Department, in 1909 

• pH means ‘the power of hydrogen’.• Each value of pH means the H+ concentration changes by a 

factor of 10• As the H+ concentration decreases, the OH‐ concentration 

increases

pH 1 pH 7 pH 14strong weak neutral weak strongacid acid base base

The pH scale according to the late Dr. Hubert Alyea, Princeton University

Page 33: Chemical Principles Visualized 23ICCE Toronto Principles Visualized 23ICCE.pdfChemical Principles Visualized: Lecture demonstrations and activities David A. Katz Chemist, educator,

pH values for some common substances

Page 34: Chemical Principles Visualized 23ICCE Toronto Principles Visualized 23ICCE.pdfChemical Principles Visualized: Lecture demonstrations and activities David A. Katz Chemist, educator,

Acids, Bases, and pH

• Acids, bases, and pH using red cabbage paper– Buffers for reference– Solutions of household products

• Illustrate indicator colors using serial dilutions to observe color changes

Page 35: Chemical Principles Visualized 23ICCE Toronto Principles Visualized 23ICCE.pdfChemical Principles Visualized: Lecture demonstrations and activities David A. Katz Chemist, educator,

Intermolecular ForcesWhy does a substance dissolve?

Page 36: Chemical Principles Visualized 23ICCE Toronto Principles Visualized 23ICCE.pdfChemical Principles Visualized: Lecture demonstrations and activities David A. Katz Chemist, educator,

Course syllabi and experimentscan be found at

http://www.chymist.com

On the left‐hand menu, click on Compleat Chymical Demonstrator 

or Magic Into Science

or, for course information and experiments,  Pima Chem Courses

then click on appropriate course link:Chem 121,  Chem 125,  Chem 130,

Chem 151, or  Chem 152