Q = cmT Q lost = Q gained
Exercise 39 - Building Models of Molecules
176 | P h y s i c a l S c i e n c e L a b o r a t o r y I n v e s t i g a t i o n s
Figure 1 Molymods by Sonia licensed under CC BY 3.0
177 | P h y s i c a l S c i e n c e L a b o r a t o r y I n v e s t i g a t i o n s Element Symbol Color of Sphere
Bromine Br Orange
Hydrogen H Yellow
Carbon C Black
Nitrogen N Light Blue
Oxygen O Red
Chlorine Cl Green
Iodine/Fluorine I or F Purple
Pre-Lab:
A. How many electrons are shared?
a. Single bonds b. Double bonds c. Triple bonds
B. Determine the number of unpaired electrons for each element contained in the kit.
Element Symbol Number
Unpaired Electrons
Bromine Br
Hydrogen H
Carbon C
Nitrogen N
Oxygen O
Chlorine Cl Iodine/Fluorine I or F Procedures:
You will build and sketch several models of molecules.
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Actual Model Sketch
Methane molecule CC SA 4.0
Notes: Molecules that contain carbon may have more than one structure possible.
Triangle and square structures are usually not valid.
1. Complete all tasks for each of the molecules listed. You may use colored pencils as long as you include a key for the colors you choose. Each atom must be identified in each molecule.
→ Build the molecule
→ Check that every hole is filled
→ Sketch the model of the molecule (attempt to show any three-dimensional structure)
→ Analyze the structure and record whether the molecule is polar or non-polar
2. Molecules containing Single Bonds a. Hydrogen, H2
b. Bromine, Br2
c. Carbon Monoxide, CO d. Water, H2O
e. Hydrogen Chloride, HCl f. Hydrogen Bromide, HBr g. Hydrogen Peroxide, HOOH h. Iodine Chloride, ICl
i. Methane, CH4
C
l C
l
C l C
l C
179 | P h y s i c a l S c i e n c e L a b o r a t o r y I n v e s t i g a t i o n s j. Dichloromethane, CH2Cl2
3. Molecules containing at least one Double Bond a. Oxygen, O2
b. Ethylene, C2H4
c. Nitroxyl, HNO d. Nitrous Acid, HONO e. Formaldehyde, H2CO f. Formic Acid, HCOOH
g. Chloroethene (vinyl), C2H3Cl h. Carbon Dioxide, CO2
i. CycloPropene, C3H4
4. Molecules containing at least one Triple Bond j. Nitrogen, N2
k. Acetylene, C2H2
l. Cyanic Acid, HOCN 5. Some common substances
m. Ozone, O3
n. Ammonia, NH3
o. Ethanol, C2H6O p. Acetic acid, C2H4O2
Analysis:
1. Look at the models for methane and dichloromethane. How are they similar? (choose one) a) Same structure
b) Same elements c) Polarity
d) Same chemical formula
2. Explain the symmetry plays in polarity. Provide an example.
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3. Organic compounds are those that contain carbon. What percentage of the models you constructed are organic?
General Questions:
1. Describe or sketch the different structures possible for C3H4. Do you expect these substances to have the same or different properties?
2. The structure of a water molecule causes it to be polar. If the water molecule had the structure illustrated below, would it still be polar? Explain.
H O H
181 | P h y s i c a l S c i e n c e L a b o r a t o r y I n v e s t i g a t i o n s
Exercise 40 - Melting Wax & Cooking Sugar
Student Learning Objectives:
Observe thermal decomposition of two compounds, and analyze chemical equations to determine the products.
Materials:
Paraffin Wax Candle 3 Ice Cubes
2 Aluminum Pie Tins Heat Source
Metal Tongs Heat Gloves Matches Aluminum Foil Granulated Sugar Plastic Spoon
Note: the thermal decomposition of sugar should be performed in a chemistry hood if possible to avoid setting off a fire alarm.
Introduction:
Most of the substances you see around you are a combination of elements; they are compounds. Many compounds contain similar elements, and 90% of compounds contain carbon. When energy is added to a substance, the compounds can be broken into new
products; this is a chemical reaction. As a candle (C25H52)burns in the oxygen (O2) provided by air, new substances will result. When sugar (C12H22O11) is heated, the molecule will split into three products. Both wax and sugar contain the same base elements of carbon and hydrogen, so thermal decomposition of these two substances results in the same products.
182 | P h y s i c a l S c i e n c e L a b o r a t o r y I n v e s t i g a t i o n s Pre-Lab:
A. Compare the wax molecule and sugar molecule and describe at least two differences.
B. Define condensation.
Warnings:
• Be careful not to burn yourself
• Excessive heating of the sugar may result in a fire alarm Procedures:
You will burn a candle and heat sugar.
Melting Wax
1. Place 3 ice cubes in one aluminum pie tin, and add a "splash" of water. Your goal is to have a little ice water in the pie tin.
2. Use the aluminum foil to create a candle stand.
3. Light the candle (C25H52) and use the metal tongs or heat gloves to hold the pie tin containing the ice water above the flame of the candle; the pie tin should be held about 1 centimeter above the flame for 2 minutes. Remove the pie tin from above the candle and hold it such that you are able to see the bottom of the pie tin. If there is nothing on the bottom of the pie tin, re-position the pie tin above the candle for another 2 minutes. After 2-4 minutes, record whether a liquid has condensed on the bottom of the pie tin. Also record whether there is a black soot on the bottom of the pie tin.
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4. Use a paper towel to remove any substances from the bottom of the ice water pie tin. Keep the ice water; you will need to use it again.
Cooking Sugar
5. Set up your heat source.
6. Add 1 spoonful of sugar (C12H22O11) to the second aluminum pie tin.
7. Use tongs and/or heat gloves to position the pie tin containing sugar in direct contact with your heat source. Once the sugar begins to change color and a gas is observed leaving the sugar, position the ice water pie tin 1 centimeter above the sugar pie tin, with the pie tins as close together as possible but not touching. After a few seconds, check the bottom of the ice water pie tin for moisture. If there is nothing on the bottom of the pie tin, re-position the pie tin above the candle for another few seconds, unless the sugar is beginning to burn. As soon as you see moisture on the bottom of the ice water pie tin, stop the experiment and remove the sugar from the heat source. Prolonged cooking of the sugar may set-off the fire alarm.
8. Turn off the heat source. Record whether a liquid has condensed on the bottom of the ice water pie tin pan. Also record the appearance of the contents in the sugar pie tin.
Clean-up:
• Rinse and dry the ice water pie tin
• Rinse the sugar pie tin and discard it in the trash
• Clean your laboratory table top
• Throw away foil used as a candle stand