Dinitrogen tetroxide and nitrogen dioxide coexist in the following equilibrium

Lab Report

Sample Lab report:

When writing your lab report, use this sample to guide you when you are writing your reports for lab. Each section of the lab report should be written in your own words and any work that is put into your report that is not your own should be cited under the ACS (American Chemical Society) citation format. More information on citations will be posted below. If you have any other questions regarding the lab report format, please do not hesitate to ask me.

Purpose:

The purpose is the most important part of the lab report. This section should contain no more than 500 words and should include the following: Objective (what will be accomplished), a brief description of how the objective will be accomplished, your quantitative results and a quick conclusion of the experiment.

Example: In this experiment, chromatography was used to analyze amino acids in solution. Standards were used to identify unknown amino acids in a mixture. Ascending layer chromatography with an isopropanol-based solvent was used to separate the amino acids, which were then detected with ninhydrin. The unknown mixture analyzed was found to contain aspartate and histidine. It was observed that hydrophobic amino acids were most mobile. This technique was shown to be an effective way of analyzing unknown mixtures of amino acids.

Introduction:

The introduction of any lab report should contain information about what you will be doing in the experiment. This includes a background information about the experiment, principles and theories (what topics you are currently learning that will help you better understand the material, important equations and calculations that will be used in the experiment), and the importance of the experiment (why this work needs to be done). This section needs to be written in your own words, but you can also paraphrase some work from other sources, with proper citation. When writing lab reports, you must write in 3rd person (do not include I, we, us, etc.).

Example: Nitrogen dioxide (NO2) is a red-brown toxic gas that is a main atmospheric pollutant in various metropolitan areas around the world. It has a higher molecular mass and density over air. Dinitrogen tetroxide (N2O4) is a dimer compound that is used in reaction with water for production of nitric acid (HNO3). It also exists as a colorless gas in the atmosphere, but not as toxic as NO2. Both chemicals can coexist with another in high temperature in the following chemical equilibrium reaction:

2 NO2 ⇌ N2O4 (1)

where for every two moles of NO2 molecules used up, one mole of N2O4 will be produced.

Equilibrium responds to changes in pressure, temperature, and concentrations of reactants and products. Quantities to be measure in this experiment include Keq(T), ΔG°, ΔH°, and ΔS°. Specifically the quantities to be measured can be accomplished by investigations of the effect of temperature on equilibrium through the pressure produce by the system. The equilibrium constant (Keq) can be acquired by the following expressions:

K(T)eq = (2)

At an arbitrary stage of the reaction, the reaction Gibbs energy can be describe in terms of potential energy which can be rearrange to the following:

ΔrG = µB - µA = (µBø + RT lnPB) – (µAø + RT lnPA)

ΔrG =ΔrGø + R lnQ (3)

At equilibrium ΔrG = 0. Furthermore, the equilibrium constant is related to the reaction free energy change as follows:

ΔrGø = - RT lnK(T)eq (4)

The standard reaction enthalpy can be obtained with the van’t Hoff equation:

= (5)

When lnK is plotted against 1/T, a straight negative line with slope equal to -ΔrHø/R is obtained. By multiplying against the gas constant, the standard reaction enthalpy is obtained.

The standard reaction entropy can then be obtained by substitution of ΔrGø and ΔrHø values into equation (6) below:

ΔrGø = ΔrHø – TΔrSø (6)

In this experiment, a metallic bulb filled with NO2 will be heated up to 90°C in 6°C to 8°C increasing increments for a series of 8 readings, recording temperature and pressure (Torr) changes for each reading. After the last reading, a final reading of 120°C is recorded to identify P0, at which N2O4 is most stable during equilibrium.

Experimental Procedures:

This section is split into two parts: Materials and Methods. Materials can be listed as bullet points and include reagents (chemical compounds and solutions), glassware and instruments used. The Methods section are the procedures from the lab manual or handout. Though it is preferred that you write the methods in your own words, you may paraphrase the instructions from the lab manual or handout.

Example: As described in the lab manual ice was placed in a beaker and warmed until approximately 50% had melted. The temperature of the ice/water mixture was then measured with a thermometer. This was followed by a similar measurement of our solid unknown. In part II, water was heated until boiling and the temperature of the liquid/gas mixture measured with a thermometer. This was followed by a similar measurement using our unknown compound. To get the best results possible, the procedure in the manual was modified by repeating each trial three times.

Data:

The data section is where you input the data recorded from the experiment you performed. If you have multiple readings or values, it is best to put them into a table, with labeled titles for each row and column of a table. Other information that was not taken in multiple readings do not need a table, but you may input them into one, if you wish. Any data points that you deem is an outlier due to error (human or environmental), please state why you excluded it from your report.

Example:

Table 1. Observations from

Mass measurements

Data (in grams, g)

Mass of crucible and lid (before heating)

25.3664 g

Mass of crucible and lid (after heating)

25.4789 g

Mass of copper wire

2.0142 g

Mass of crucible + lid + wire

27.0931 g

Mass of crucible + lid + wire + sulfur

30.1486 g

Results/Discussion:

The results and discussion section coincide with one another, but are two different parts. The results section is where you input concluding values from the experiment, such as averages, standard deviations, masses/volume of final products and other important values. Calculations of these values must also be inputted to validate your results. If you require a graph to calculate unknown values, it must be plotted, properly labeled (title of graph and axes) and posted on the report. Results may be written in words, but is not necessary.

For the discussion section, you must discuss your findings in the experiment. If this requires you to compare your calculated results to literature values (such as “true values”), you must explicitly state your thoughts. You must also discuss any errors that occurred in the experiment, whether it be human or random error. Any discussion questions found at the end of the experiment protocol must be answered here as well.

Example:

Results:

Table 2. Results from heating sample

Mass measurements

Data (in grams, g)

Mass of crucible + lid + contents (first heating)

31.0264 g

Mass of crucible + lid + contents (second heating)

31.0263 g

Mass of crucible + lid + contents + additional sulfur

33.2548 g

Mass of crucible + lid + contents (third heating)

33.1478 g

Mass of copper sulfide in crucible: 31.0263 g – 25.4799 g = 5.5464 g

Mass of sulfur in sample: 30.1486 g – 27.0931 g = 3.0555 g

Mole of copper in sample: = 0.0317 mol Cu

Mole of sulfur in sample: = 0.0953 mol S

Mole ratio Cu:S: = 3

Empirical Formula Copper Sulfide: CuS3

Discussion:

Based on the results calculated on obtained, the empirical formula determined for Copper Sulfide was CuS3. According to literature values, the possible empirical formulas for copper sulfide are CuS and Cu2S. Therefore, the results obtained are incorrect. Some possible errors that occurred during this experiment is not allowing the crucible to heat up thoroughly, possible contamination in the reaction system or not allowing the reaction to go into completion.

Conclusion:

The conclusion is a brief paragraph reiterating what occurred in the experiment, the results obtained and whether your results match literature values or not. You can also talk about you can improve the experiment and what can you do to obtain better results the next time you perform the experiment.

Example: The objective of this experiment was to determine the energy content of a piece of Cheeto® by measurement of temperature increase of a water sample. The energy content calculated from the experiment was 15 calories per piece, while the energy content listed on the Cheetos® label is 12 calories per piece. One can improve on this experiment is by using a much more advanced calorimeter to obtain accurate readings, but due to budget costs, a crude, man-made calorimeter works just as well.

References:

The reference section is where you list all works cited in your lab report for justification of the introduction section. The lab protocol from the lab manual or lab handout must always be referenced here, since all the information you are getting to write your report is from the main source. Textbooks may also be referenced if using work from a specific section. Examples on how to cite work (in ACS format) are below:

Books: (Author(s) Last Name, First and Middle Initial, Chapter Title. Book Title, Edition number, Publisher, Place of Publication, Year; Page Number.)

Gilbert, T.R.; Kirss, R.V.; Foster, N.; Bretz, S.L.; Davies, G. Acid-Base Titrations and Equilibrium. Chemistry: The Science in Context, 5. W.W. Norton and Company, United States of America, 2017; 354-369.

Internet Resources: (Author(s), if any. Title of Site. URL (date accessed), other information)

Chemical Equilibrium. http://www.chem1.com/acad/webtext/chemeq/Eq-01.html (Aug 31 2017).

Journal Publication/Article: (Author(s) Last Name, First and Middle Initial, Title of Artcle. Journal Abbreviation (if available), Year Published, Volume, Page Number)

Tadle, A.C.; Garcia-Ramirez, E.S.; Montoya, G.A.; Castro, L.; Garcia, R.E.; Diels-Alder synthesis of polyaromatic hydrocarbons via enzyme kinetics. J. Am. Chem. Soc. 2015, 6, 1145-1156