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Chemical Principles Visualized:

Lecture demonstrationsand activities

David A. KatzChemist, educator, and consultant

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

Email: dakatz45@msn.comWeb site: www.chymist.com

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.

• 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.  

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

Molecular ShapesModeling clay and toothpicks to build shapes

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

Molecular Shapes

MX3triangular planar (trigonal planar)120° bond angle

Characteristic of Periodic Table Group IIIA

Molecular Shapes

MX4tetrahedral

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

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

Visual Stoichiometry

CH4 +         O2 CO2 +     H2O  (equation not balanced)

Visual Stoichiometry

H2SO4 +  2 NaOH   Na2SO4 +  2 H2O

Density

Indiana Jones – Raiders of the Lost Ark

Coke vs. Diet Coke

Hot and ColdSeparate water by density

COLD                                    HOT

HOT

COLD

Visible LightAn overhead projector spectroscope

Holographic diffraction grating (Flinn C-Spectra)

Slit and colored filters

Visible LightAn overhead projector spectroscope

Holographic diffraction grating

Slit and colored filters

The Electromagnetic Spectrum

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

Hydrogen spectrum Helium spectrum

Colored Flames

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

lithium potassium

calcium barium

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

Iodine

1. Intermolecular forces using I2

1. Iodine vapor2. Iodine‐hexane: 

Nonpolar interactions (London forces)

2. Intermolecular forces using I2

Dipole ‐ Induced dipole

3. Intermolecular forces using I2

Ion – induced dipole

4. Intermolecular forces using I2

Solubility preference:Like dissolves like Hexane 

layer

Water layer

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)

Intermolecular forces Drops of water on a coin

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

Intermolecular forces: Decrease in Volume

ethanol and water

Intermolecular forces: Decrease in Volume

ethanol water

Hydrogen BondingIncrease in Volume

HCl + NaOH NaCl + H2O

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

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

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

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

pH values for some common substances

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

Intermolecular ForcesWhy does a substance dissolve?

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