lab discussion for and the lab assignment.

(lab discussion 8.2)

This week’s laboratory will extend your knowledge of chemical bonding through interacting with virtual simulations as in week’s past. Your initial post to the forum should be in response to the following:

Discuss the relationship of calculating lattice energy and the Born-Haber cycle.

Here are some suggestions of topics on which to elaborate upon in your explanations:

• Provide an explanation of the Born-Haber cycle.
• Explain the difference between ionization energy and electron affinity.
• Explain how the enthalpy of formation is related to the Born-Haber cycle.

Your subsequent four posts to your peers and/or your instructor should further the discussion by elaborating on the objectives above. Do not include any results for your laboratory experiments. References must be provided for any content retrieved from credible sources.

(CHE 121 PROJECT Lab)

A lab-based project is a requirement for the lab portion of Principles of Chemistry I. The results of the project will be written as a report, the format of which will be the same used since the beginning of this course. The experiment will be performed in the eighth week of class, and the report will be due by the end of the term. Please read the description, guidelines, and advice that follow.

Purpose of the Project

Students taking a major’s level freshman science course should be able to analyze and report natural phenomena in a scientific manner. The writing of scientific reports and papers is necessary to advance in the scientific field.

Scientists communicate their discoveries to others via papers published in peer-reviewed journals. While I do not necessarily expect you to publish in Nature or The Journal of Physical Chemistry, nonetheless you should gain experience in the procedure to obtain at least some idea of the skills scientists must demonstrate and responsibilities they shoulder. This project is a tool to assess your ability to perform a much simpler, freshman version of the process. A large portion of your efforts this term have been procuring such styled reports of your findings, so you will rely on this experience for this investigation.

Nature of the Project

You will carry out a laboratory procedure to determine the concentrations of two unknown solutions.

Grading of the Project

The report will be scored using the rubric located in the course titled “Laboratory Report Grading Rubric.”

Format of the Report

The report will follow the same formatting guidelines as previously used in the reports for this course.

Expectations

• -All experiments are to be completed individually.
• -All reports are to be formatting as indicated in the formatting guidelines.
• -Late submissions will not be accepted.

PROJECT TOPIC

Reading Assignment:

Vo, Kevin. (2019, September 19). Spectrophotometry. Chemistry LibreTexts. https://batch.libretexts.org/print/Letter/url=https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Kinetics/Reaction_Rates/Experimental_Determination_of_Kinetcs/Spectrophotometry.pdf

Using the Spectrophotometer

The experiment will be conducted using the virtual spectrophotometer located in the Week 8 module titled “Spectrophotometer Lab.”

Procedure

Note: You will record your data in the table following this section. The data table must be including in the ‘Results’ section of your report. All calculations carried out must be provided in report.

1. Determination of Molar Absorption Coefficient:

1. Select a blank cuvette and place it in the spectrophotometer. Close the lid.
2. Click on 0 ABS 100%T button, the instrument now reads 0.00000 A.

1. Choose the solution of CoCl₂ solution with known concentration and measure the absorbance between the wavelengths 350 nm to 700 nm. Record this data in Table 1.
2. Note the wavelength at the maximum absorbance value in Table 1. You will need to provide this in your report.

1. Calculate the value of molar absorption coefficient using the equation

where,

ε = molar absorption coefficient
A = maximum absorbance of known concentration solution
c = concentration of solution (given in simulation)
l = cuvette length (given in simulation)

• B.Determination of Unknown Concentration:

1. Set the wavelength to the value corresponding to maximum absorbance (recorded above).
2. Place the cuvette with same solution but at an unknown concentration.
3. Record the absorbance for this wavelength in your notes.
4. Refresh your page and repeat the same procedure for a second solution of your choice. You must indicate your selection of solution and the resulting concentration in your report. Provide all associated data and calculations.

1. Calculate the concentration with the help of the equation,

where,

ε = molar absorption coefficient determine from previous procedure
A = maximum absorbance of current concentration solution (not previous procedure)
l = cuvette length (given in simulation)

Notes on Real Laboratory Practices

1. Always wear lab coat and gloves when you are in the lab. When you enter the lab, switch on the exhaust fan and make sure that all the chemicals and reagents required for the experiment are available. If they are not available, prepare the reagents using the components for reagent preparation.
2. Make sure to clean all your working apparatus with chromic acid and distilled water and ensure that all the apparatus are free from water droplets while performing the experiment.
3. Make sure to calibrate the electronic balance before taking the measurements.
4. Ensure that the spectrophotometer is working properly.
5. Ensure that you are handling the cuvette with tissue paper. Never touch it with your bare hand.
6. Wipe the cuvette with tissue paper before placing the spectrophotometer.
7. Clean all glassware with soap and distilled water. Once the experiment is completed recap the reagent bottles. Switch off the light and exhaust fan before leaving the lab.
8. Discard the used gloves in a waste bin.