Activity
Molecular Geometry and Shape
Materials
For each pair of students
One Model Kit
Complete the following chart by building a model of each molecule
Formula
Name
Lewis Dot Structure_
Drawing of Molecule Model
A
angement
of Electron Pairs
Molecula
Shape
0. H2O
Wate
_
H – O – H
tetrahedral
ent
1. NH3
2. CO2
3. CHCl3
Formula
Name
Lewis Dot Structure
Drawing of Molecule Model
Geometry
Shape
4. HC2H3O2
Hint: Three centers
5. NO31-
6. N2H4
Hint: Two centers
7. C2H2
8. HCN
Formula
Name
Lewis Dot Structure
Drawing of Molecule Model
Geometry
Shape
9. CH4
10. O3
11. PH3
Hint: Blue for P
12. N2
13. BH3
Formula
Name
Lewis Dot Structure
Drawing of Molecule Model
Geometry
Shape
14. CH2O
15. C2H6
Hint: Two Centers
16. H3O+
Hint: Use blue for oxygen
Usual Colors (there will be some exceptions):
Chem 121 XXXXXXXXXXHa
y S Truman College
Page 4 of 4
Prof. Joy Walke
Black = Ca
on
Red = Oxygen
Blue = Nitrogen
Yellow = Hydrogen
Green, Orange = Halogen
For other atoms pieces of any color that have the proper holes in the model may be used. Use springs for double and triple bonds.
CHEM 121 Lab XXXXXXXXXXSummer 2020
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Lab Experiment or Simulation
CHEM 121 - Online Lab - Calorimetry
Introduction
Heat is a form of energy which measures the total kinetic energy of the particles of a substance Temperature, on the other
hand, measures the average speed of the motion of particles The higher the temperature, the faster the particles in a
sample of matter are moving The lower the temperature, the slower the average speed of the particles. Heat flows from a
higher-temperature to a lower-temperature region Calorimetry is the science of measuring the quantity of heat of a
substance The apparatus used to measure the heat is called the calorimeter.
Heat (q) is calculated mathematically based on the change in temperature of a substance (ΔT), the mass of the substance
(m), and a quantity called the specific heat capacity of the substance (Cs). The specific heat capacity is the amount of heat
equired to raise the temperature of one gram of a substance by one degree Celsius. The specific heat of water is 4.184
J/g°C or 1 cal/g°C. Many substances have a much lower specific heat than water. Copper, for example, has a specific heat
of 0.385 J/g·°C. In effect, much less energy is required to raise the temperature of a certain mass of copper than to raise
the temperature of an equal mass of water.
The heat is calculated as follows for 100 g of water that experiences a rise in temperature from 25.0°C to 45.0°C:
q = m × Cs × ΔT
q = (100 g XXXXXXXXXXJ/g°C)(45.0°C - 25.0°C)
q = 8.37 × 103 J = 8.37 kJ
This shows the amount of heat required to raise the temperature of 100 g of water by 20°C If the substance had been
copper instead the same temperature rise would have required only 770 J. The amount of energy in the entire universe is
understood to be constant This idea is called the First Law of Thermodynamics It assumes that the universe is composed
of a system and its su
oundings The heat abso
ed or given off by the system (qsys) is exchanged with the su
oundings
(qsur), which is expressed mathematically as follows:
qsys = -qsur
The minus sign in the equation implies that the heat flows in opposite directions relative to the system and its
su
oundings We will use this law in order to understand and interpret our work in this lab A metal cylinder will represent
a system and water will be used as its su
oundings We will determine the speci c heat capacity of metal by using a
coffee-cup calorimeter, assuming that no heat is exchanged through the walls of the insulated container. You will use the
following equation to calculate the speci c heat capacity of unknown metal:
Qmetal = -qwater
Qmetal = heat lost by the metal
= mass of metal (mm) × specific heat capacity of metal (Csm) × change of temperature of metal (ΔTm)
qwater = heat gained by the water
= mass of water (mw) × specific heat capacity of water (Csw) × change of temperature of water (ΔTw)
Sample Calculation
A calorimeter (two nested Styrofoam cups) is lled with 175.0 g of water at an initial temperature of 25 0°C. A quantity of
water is heated to 100.0 °C, then 25.0 g of aluminum is heated in the boiling water for five minutes. Once the aluminum
CHEM 121 Lab XXXXXXXXXXSummer 2020
17
has the same temperature as the boiling water, it is removed with a pair of tongs and placed into the water in the
calorimeter. What is the specific heat capacity of the piece of aluminum if the nal temperature is 27.2°C?
qAl = (25.0 g)(CsAl)(27.2°C XXXXXXXXXX°C)
qH2O = XXXXXXXXXXg XXXXXXXXXXJ/g°C)(27.2°C - 25.0°C)
qmetal = -Qwater
(25.0 g)(CsAl)(27.2°C XXXXXXXXXX°C) = -[(175.0 g XXXXXXXXXXJ/g°C)(27.2°C - 25.0°C)
CsAl = 0.897 J/g°C
This example was written so that the answer gives the accepted reference value for the specific heat of aluminum metal
Your work in the lab will involve a similar measurement.
Accessing the Simulation
1. Launch a web
owser application using either Chrome or Firefox.
2. Access the online VIRTUAL LAB: Calorimetry - Specific Heat of a Metal at
http:
dbpoc.com/pearson/chemsims/gold/calorgold5/Calor.php
a. Select the Experiment tab.
. Then, click on Run Demonstration.
i. This will take you on a step by step tutorial on how to perform a calorimetry experiment
with specific substances (liquid and/or solid)
Instructions & Data Collection
Use the following instructions to complete the virtual lab and collect the necessary data. Document the required data
values as you complete the virtual lab. All work will later be submitted in Brightspace.
Experimental Procedure
The experimental setup shows a beaker on a hot plate to the left, and a calorimeter on the right. Below the beaker and hot
plate are three tabs (Liquids, Solids and Solutions).
In this activity you will be using the Solids tab beneath the beaker and hotplate, and the Liquids tab beneath the
calorimeter.
http:
dbpoc.com/pearson/chemsims/gold/calorgold5/Calor.php
CHEM 121 Lab XXXXXXXXXXSummer 2020
18
Part A: Heat Transfer between metal and water
1. Beneath the beaker and hot plate click on the Solids tab and select Aluminum, Al.
2. Adjust mass to 20.0 g and adjust the temperature to 200. °C.
3. Click the Next button in the left frame near the bottom of the screen.
4. Now click on the Liquids tab beneath the calorimeter and add XXXXXXXXXXg of water and adjust the water temperature
to 20.00 °C.
5. Record the initial conditions in Table 1.
6. Next, in the Run Experiment section
a. Click on Show Graph View, and Show Microscopic View
. Then, click on the Start button.
c. Record your observations on what is happening.
d. Take a screenshot of the experiment while it is running. Remember to upload this in the Post-Lab
activity section for this experiment on Brightspace.
Table 1: Heat Transfer between Known Metal and Water
Metal Water
Name of Metal, Formula Aluminum, Al Water, H2O
Mass (g)
Tinitial (oC)
Tfinall (oC)
Change in temperature, ΔT
In the space below, show all calculations for each step with co
ect units and significant figures.
Observations: Summarize and record your observations while running the experiment. What do you observe happening?
Record the final conditions of Al and the water in the table above.
CHEM 121 Lab XXXXXXXXXXSummer 2020
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Part A - Data Analysis and Interpretation (Post-Lab Questions)
Using the graph below, draw the resulting relationship between Temperature and Time.
● How do the two lines on the graph compare?
● What is the main conclusion you can draw from the graph?
A. Answer the following questions.
1. Which substance, Al or water, loses heat when they are combined?
2. Which substance, Al or water, gains heat when they are combined?
3. Which process is endothermic and which is exothermic? Explain your reasoning in 1-2 sentences.
4. Calculate the heat (q) transfe
ed to or from Al. Use the equation q = mC∆T. Show
all work including units and significant figures.
5. Calculate the heat (q) transfe
ed to or from water. The specific heat of water is 4.184 J/goC.
CHEM 121 Lab XXXXXXXXXXSummer 2020
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6. Compare the heat values associated with the metal and water. Make a generalization concerning these heat values.
7. How would your results have been different if you had used different amounts of metal and