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:

• To enhance your ability to perform stoichiometric calculations.
• 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

• From the course home page, click on the Virtual Lab Tutorial link to watch the overview of using the virtual lab.
• From the course home page, access the lab environment by clicking on the Virtual Lab link.
• After the lab environment loads, click ‘File’ then ‘Load an Assignment.’
• Select the ‘Stoichiometry and Limiting Reagents’ category.
• Select the ‘Textbook Style Limiting Reagents Problems’ assignment.
• At this point, you have prepared the laboratory for the first experiment with the require supplies to complete your experiments.
• 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.
• 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.
• 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.
• Return to the ‘Solutions’ table in the stockroom and obtain the Erlenmeyer flask containing the ‘1.00 g AgNO₃.’
• 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 “aluhkwaat” and is typically used to describe small samples of a whole in chemical analyses.)
• 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.
• 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.
  qq
• 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.
• After you record your data, clear the workbench but do not close the virtual lab!
• 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.
  • 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?
  • 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?

Performing the Experiment

Data Analysis

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.

• Define the problem in a manner that is clear and insightful.
• Identify the strategies and procedures used during the lab.
• Clear hypothesis statement and other potential solutions that identify any relevant contextual factors (i.e. real-world costs).
• 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.
• Clearly stated results and discussion of possible improvements to the procedure.
• 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:

• Does my problem statement make sense?
• Have I summarized my strategies/procedures well enough to be replicated by an outsider?
• Did I have a valid hypothesis at the start of the lab? Have I expressed this in my report?
• Do my tables and/or graphs make sense?
• Are my conclusions valid based on my supplied data?
• 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?