Background:
Balanced chemical equations provide a vast amount of information and are
a shorthand notation that can be understood by chemists and other scientists
alike. For example, a very quick inspection of the balanced chemical equation
below shows that the reactants and products are easy to discern from one
other simply by identifying the chemical species on the left or right of the
arrow.
2H2(g) + O2(g) → 2H2O(l)
Figure 1: Reaction of hydrogen gas and
oxygen gas to produce liquid water. The reactants are to the left of the arrow
and the product to the right.
Further, the whole-number coefficients give the relative amounts of the
species with respect to one another; this enables chemists to quickly acquire
some quantitative information that could be useful in the laboratory. These
quantitative relationships or quantitative deductions drawn from the balance
chemical equations (and subsequent calculations) can be grouped under a single
umbrella term called stoichiometry.
In this laboratory, we will be investigating the stoichiometric
relationship involving the reaction of sodium chloride (NaCl) and silver
nitrate (AgNO3). When combined, these reactions will produce stoichiometric
amounts of sodium nitrate (NaNO3) and solid silver chloride (AgCl). Take
a moment to formulate and write down a hypothesis about this reaction and its
stoichiometry.
This chemical reaction can be seen below in the form of the complete and balanced
molecular equation. As one can infer from this brief introductory information,
a thorough knowledge of the associated chapters reading for this week is
critical to performing well; you are encouraged to read these required sections
before starting this lab.
NaCl(aq) +
AgNO3(aq) → AgCl(s) + NaNO3(aq)
Figure 2: The balanced molecular equation
for the reacting chemical species in this laboratory.
There are several
objectives of this lab:
1.
To enhance your ability to perform stoichiometric calculations.
2.
To improve your comprehension of the various types
of chemical reactions.
Before you start this laboratory assignment, you are encouraged to review
Section 4.3 on page 193 in the textbook. Throughout this laboratory assignment,
you will be required to perform and thoroughly document your calculations
pertaining to the stoichiometry associated with the reaction above. Be sure to
record all observations and any relevant notes that you think you will need to
include in your laboratory report.
Procedure:
Preparing the Lab
I
1. From the course
home page, click on the Virtual Lab
Tutorial link to watch the overview of using the virtual lab.
2. From the course
home page, access the lab environment by clicking on the Virtual Lab link.
3. After the lab environment
loads, click ‘File’ then ‘Load an Assignment.’
4. Select the ‘Stoichiometry
and Limiting Reagents’ category.
5. Select the ‘Textbook
Style Limiting Reagents Problems’ assignment.
6. At this point, you
have prepared the laboratory for the first experiment with the require supplies
to complete your experiments.
7. If you haven’t
already done so, formulate a hypothesis about the stoichiometry of the reaction
between NaCl and AgNO3 as you will need to include this in your
final report.
Performing the
Experiment
8.
Select the ‘Solutions’ tab in the stockroom if it is
not already selected. Then, select the Erlenmeyer flask containing the ‘1.00 g
NaCl’ to move it to the workbench.
9.
We will now collect some data about this solution in
the ‘Information’ pane. Record the values for the concentration (molarity) for
the Na+ and Cl- species in your notes. Before moving to
the next step, you will need to calculate the number of grams of each species;
record your calculations and resulting answers in your electronic or
handwritten notes.
10.
Return to the ‘Solutions’ table in the stockroom and
obtain the Erlenmeyer flask containing the ‘1.00 g AgNO3.’
11.
Add 100 mL of H2O to the flask. Remember,
in a real laboratory setting you cannot accurately add small volumes of water
from a very large container, so you will need to transfer a small aliquot of
water to a beaker or other piece of glassware before transferring the required
amount to the flask. (The term ‘aliquot’ is pronounced as “a·luh·kwaat” and is
typically used to describe small samples of a whole in chemical analyses.)
12.
Once your transfer is complete, obtain the concentrations
of the NO3− and Ag+ ions from the
‘Information’ pane as before. Then, calculate the grams of each species and
record it in your notes.
13.
At this point, we now have the necessary agents
needed to perform the reaction. Add the entire amount of the NaCl solution to
the flask containing the AgNO3 solution using the ‘Realistic’ pour
feature in the dialog box. You will see the ‘Realistic’ option once you click
and drag the flask to the other.
14.
Select the flask containing the mixed reagents and
open the ‘Information’ pane. Record the data for the NO3−, Ag+,
Na+, and Cl− ions as well as the grams of AgCl formed.
15.
After you record your data, clear the workbench but
do not close the virtual lab!
Data Analysis
16.
Before completing this lab, you will need to conduct
a thorough analysis of your data in order to answer the mandatory questions
below. You will need to include your responses to these questions in your
written report in the appropriate section(s). You can use the virtual lab to
investigate answers to these questions.
a.
The solution labeled ‘Solution 1’ in the Stockroom
contains 2.00 g NaCl. How many grams of AgNO3 must be added to the solution to
the solution to completely react with NaCl according to the reaction in the background
section?
b.
The solution labeled ‘Solution 2’ in the Stockroom
contains 3.00 g NaCl.If excess NaCl is added to the solution, how many grams of
AgCl solid will be formed?
17.
Notes
This section should
include notes about any observations or data collected during the lab.
Report Requirements
This section
contains key information that must be included in your typed report.
1. Define the problem in a manner
that is clear and insightful.
2. Identify the strategies and
procedures used during the lab.
3. Clear hypothesis statement and
other potential solutions that identify any relevant contextual factors (i.e.
real-world costs).
4. Clear presentation of data
including any tables or other figures that are relevant to understanding your
stated conclusions at the end of the report. Include any relevant calculations
performed during the lab.
5. Clearly stated results and
discussion of possible improvements to the procedure.
6. Conclusive statements arguing
in favor of your findings.
Note: All reports will be graded using the rubric embedded within the course.
Here are some questions to
consider as you write your report:
1. Does my problem statement make
sense?
2. Have I summarized my
strategies/procedures well enough to be replicated by an outsider?
3. Did I have a valid hypothesis
at the start of the lab? Have I expressed this in my report?
4. Do my tables and/or graphs
make sense?
5. Are my conclusions valid based
on my supplied data?
6. Did I thoroughly summarize my
laboratory experience in a concise, factual way such that the reader can
understand my processes and findings in the conclusion section alone?
