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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,](https://reader033.vdocument.in/reader033/viewer/2022042606/5f761acaf8ff7d391c4a81c2/html5/thumbnails/1.jpg)
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,](https://reader033.vdocument.in/reader033/viewer/2022042606/5f761acaf8ff7d391c4a81c2/html5/thumbnails/2.jpg)
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.
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• 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.
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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
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Molecular ShapesModeling clay and toothpicks to build shapes
MX2 – linear, 180° bond angle Characteristic of Periodic Table Group IIA
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Molecular Shapes
MX3triangular planar (trigonal planar)120° bond angle
Characteristic of Periodic Table Group IIIA
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Molecular Shapes
MX4tetrahedral
109.5° bond angleCharacteristic of Periodic Table Group IVAStudents must physically form a 3-D structure
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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
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Visual Stoichiometry
CH4 + O2 CO2 + H2O (equation not balanced)
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Visual Stoichiometry
H2SO4 + 2 NaOH Na2SO4 + 2 H2O
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Density
Indiana Jones – Raiders of the Lost Ark
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Coke vs. Diet Coke
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Hot and ColdSeparate water by density
COLD HOT
HOT
COLD
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Visible LightAn overhead projector spectroscope
Holographic diffraction grating (Flinn C-Spectra)
Slit and colored filters
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Visible LightAn overhead projector spectroscope
Holographic diffraction grating
Slit and colored filters
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The Electromagnetic Spectrum
Viewing spectra using holographic diffraction grating (Flinn Scientific C‐Spectra)
Hydrogen spectrum Helium spectrum
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Colored Flames
Strontium – redLithium ‐ redCalcium – red/orangeCopper – green or blueBarium – yellow‐greenPotassium – violetSodium ‐ yellow
lithium potassium
calcium barium
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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
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Iodine
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1. Intermolecular forces using I2
1. Iodine vapor2. Iodine‐hexane:
Nonpolar interactions (London forces)
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2. Intermolecular forces using I2
Dipole ‐ Induced dipole
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3. Intermolecular forces using I2
Ion – induced dipole
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4. Intermolecular forces using I2
Solubility preference:Like dissolves like Hexane
layer
Water layer
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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)
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Intermolecular forces Drops of water on a coin
How many drops of water can you put on a coin? Why?
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Intermolecular forces: Decrease in Volume
ethanol and water
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Intermolecular forces: Decrease in Volume
ethanol water
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Hydrogen BondingIncrease in Volume
HCl + NaOH NaCl + H2O
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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
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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
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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
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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
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pH values for some common substances
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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
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Intermolecular ForcesWhy does a substance dissolve?
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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