Chemical Principles Visualized: Lecture demonstrations and activities

Transcription

1 Chemical Principles Visualized: Lecture demonstrations and activities David A. Katz Chemist, educator, and consultant Tucson, AZ 85745, USA Voice: Web site:

2 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.

3 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.

4 Purchase from magic supply company or make your own Chemistry Book

5 A Chemical Genie

6 OXYGEN Joseph Priestley Carl Wilhelm Scheele

7 Carbon dioxide

8 Molecular Shapes Using 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

9 Molecular Shapes Modeling clay and toothpicks to build shapes MX 2 linear, 180 bond angle Characteristic of Periodic Table Group IIA

10 Molecular Shapes MX 3 triangular planar (trigonal planar) 120 bond angle Characteristic of Periodic Table Group IIIA

11 Molecular Shapes MX 4 tetrahedral bond angle Characteristic of Periodic Table Group IVA Students must physically form a 3-D structure

12 Molecular Shapes Molecules with non bonded electron pairs Trigonal pyramid bond angle Characteristic of Periodic Table Group VA Bent bond angle Characteristic of Periodic Table Group VIA

13 Visual Stoichiometry CH 4 + O 2 CO 2 + H 2 O (equation not balanced)

14 Visual Stoichiometry H 2 SO NaOH Na 2 SO H 2 O

15 Density Indiana Jones Raiders of the Lost Ark

16 Coke vs. Diet Coke

17 Hot and Cold Separate water by density HOT COLD COLD HOT

18 The Electromagnetic Spectrum

19 Visible Light An overhead projector spectroscope Holographic diffraction grating (Flinn C-Spectra) Slit and colored filters

20 Visible Light An overhead projector spectroscope Holographic diffraction grating Slit and colored filters

21 The Electromagnetic Spectrum Viewing spectra using holographic diffraction grating (Flinn Scientific C Spectra) Hydrogen spectrum Helium spectrum

22 Colored Flames Strontium red Lithium red Calcium red/orange Copper green or blue Barium yellow green Potassium violet Sodium yellow lithium potassium calcium barium

23 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 Dextrose (d-glucose) solution in polarized light on an overhead projector (Note: A kit is available from Flinn Scientific)

24 Iodine

25 1. Intermolecular forces using I 2 1. Iodine vapor 2. Iodine hexane: Nonpolar interactions (London forces)

26 2. Intermolecular forces using I 2 Dipole Induced dipole

27 3. Intermolecular forces using I 2 Ion induced dipole

28 4. Intermolecular forces using I 2 Solubility preference: Like dissolves like Hexane layer Water layer

29 Intermolecular forces: Salting Effects Mixture of 2 propanol and water (15 ml of each) Add food color Add 7 g ammonium sulfate and shake Test layers for conductivity Reference: J. Chem. Educ, 87, 1332 (December 2010)

30 Intermolecular forces Drops of water on a coin How many drops of water can you put on a coin? Why?

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32 Sodium polyacrylate A superabsorbent polymer

33 Intermolecular forces: Decrease in Volume ethanol and water

34 Intermolecular forces: Decrease in Volume ethanol water

35 Hydrogen Bonding Increase in Volume HCl + NaOH NaCl + H 2 O The volume increase is 18.5 ml/mol Reference: Sam Katz, and Jane E. Miller, J. Phys. Chem., 1971, 75 (8), pp

36 Hydrogen Bonding Increase in Volume Hydrated H 3 O + O-O distance 2.59 Å Hydrated OH - O-O distance 2.50 Å H 2 O O-O distance 2.82 Å Source: Martin Chaplin, index.html

37 Intermolecular Forces: Which Will Evaporate First? What factors affect evaporation? Spread these compounds on black chalkboards Water methanol ethanol 2 propanol Effect of molecular weight: H 2 O = 18 CH 3 OH = 32 C 2 H 5 OH = 46 C 3 H 8 OH = 60 Effect of polarity

38 Acids and Bases Svante August Arrhenius ( ) Acid produces hydrogen ions in water solution. Johannes Nicolaus Brønsted ( ) and Thomas Martin Lowry ( ) An acid base reaction consists of the transfer of a proton (or hydrogen ion) from an acid to a base

39 ph First introduced by Danish chemist Søren Peder Lauritz Sørensen ( ), 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 14 strong weak neutral weak strong acid acid base base The ph scale according to the late Dr. Hubert Alyea, Princeton University

40 ph values for some common substances

41 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

42 Intermolecular Forces Why does a substance dissolve?

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44 Why is the sky blue? Normal sky color Pale blue sky near horizon

45 Chemistry and Light Red sunset: The Tyndall effect or why your car s tail lights are red

46 Course syllabi and experiments can be found at 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