Chem proj help 7

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A formal chemistry lab report generally contains specific sections: title of the report,

abstract, introduction, experimental section, results and discussion, conclusions, and

references.

Title The title tells exactly what the experiment or report is about. The title is centered. The

name (s) of the student(s), address of the institution, and date come after the title. If more

than one name is on the report, an asterisk is placed by the name of the author.

Abstract: This section is a one-paragraph summary in about 100 to 200 words, usually in

boldface and single spaced. It includes the purpose and importance of the experiment or

study, the experimental method, the major results, and the conclusions drawn. Specific

information about the experiment or study must be written in the past tense. The present

tense is only used for accepted facts—concepts and principles. Please note that although

this portion of the report comes right after the title, it is the section that is written last

because it is a summary of the report.

Introduction This section provides background information (theory and previous research). It states the

goals/objectives and provides a short description of the experimental design. The past

tense is used except for well-established facts. A separate paragraph is used for each major

point. Sources used must be properly cited. Generally, in-text citations are indicated either

as numeric superscripts, italicized numbers in parentheses, or author surname-year in

parentheses.

Experimental Section

This section usually comes after the “Introduction” section in scientific journals and is in

two parts: Methods and Materials and Procedure. The first part outlines the methods

and materials used. Well-known methods and materials are generally referenced rather

than written out. The “Procedure” follows the materials and methods. (For your report,

you will write procedure only.) Complete sentences in the past tense and passive voice are

used in this section. Subject pronouns such as “I” or “we” should be avoided. The steps in

an experiment are not numbered. If an experiment involves two or more different

activities, each activity must be clearly identified with subheadings.

Results and Discussion This section comes after the procedure in the "Experimental Section." This section gives

the data and results and a discussion of the results. The major focus in this section is on

calculations, tables, graphs, errors, and deviations. Here we compare the results obtained

from the experiment with the expected results. If the results are what you expected,

indicate which theory or law they are consistent with. If results are inconsistent with

expected results, account for the errors. The past tense is used to discuss the experimental

findings and present tense is used for accepted facts and scientific principles.

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Conclusions This section comes after the “Results and Discussion” section. It states what you discover

after performing the experiment.

References In this section, the sources cited in the rest of the writing are listed. Note that “references”

is different from “bibliography.” “References” is a list of sources of information you had

cited in the lab report. “Bibliography” is a list of sources of information from which you

obtained general knowledge of a particular topic without directly quoting from it.

In some journals, references are placed at the end of the article; in others, they are indicated

as footnotes. Journals published by the American Chemical Society (ACS) utilize two

methods of citing references: by superscript numbers, or by italic numbers in parentheses.

Your instructor may specify which method you should use. If none is specified, you may

select one method and use it consistently for the entire report.

For example, in the body of the text, the literature value is assigned a “reference number”

as shown:

The BP is given as 67°C in the literature.1

The BP is given as 67°C in the literature (1).

At the end of the report, all the reference sources are listed in numerical order. Having

the list of references at the end of the report is the easier method than to have them as

footnotes. Below are examples of how references are to be listed according to the ACS

Style guide.

UNPUBLISHED DATA (such as data from fellow classmates):

Smith, J. CCBC-Catonsville, personal communication, Feb 2015.

BOOK:

Author’s last name, initials, Title (in italics), edition; Publisher: City, State (in 2

letters), Year; Pages or Chapter.

Malone, L. J. Basic Concepts of Chemistry, 7th ed.; John Wiley & Sons: St.

Louis, MO, 2004, pp 145-148.

HANDBOOK:

CRC Handbook of Chemistry and Physics, 81st ed. Lide, D.R., Ed.; CRC

Press: Boca Raton, FL, 2000-2001; p. 4-73.

JOURNAL:

Author’s last name, initials (separated by semicolon if more than one). Title of

Journal (italics). Year (bold), Volume (italics), Page.

Liu, S.; Armes, S. P. J. Am. Chem. Soc. 2001, 123, 9910.

SAMPLE FORMAL LAB REPORT

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A Sample Formal Report

Determination of the Concentration of an Aqueous

Solution of HCl

Jane Smith and John Doeber*

The Community College of Baltimore County

7201 Rossville Blvd, Baltimore, MD 21237-3899

June 9, 2015

Abstract: The purpose of the experiment was to determine the concentration of an aqueous solution of HCl (Unknown #159). A solution of NaOH of known

concentration (0.1000 M) was used to titrate against the solution of HCl with

phenolphthalein as the indicator. Three trials were performed and the average

concentration of the HCl solution was found to be 0.1475 M with an average

deviation of 0.07%, and an error of 2.9%.

Introduction Titration1 is a technique that can be used to determine the concentration of a solution by

carefully reacting it with another solution of known concentration. In this experiment, the

titration method is used to determine the concentration of an HCl solution. This was done by

titrating a sample of the solution against a solution of NaOH of known concentration. The

reaction involved is as follows:

HCl (aq) + NaOH (aq)  H2O (l) + NaCl (aq)

Phenolphthalein was used as the indicator which changes from colorless when acidic to pink

when basic. With the HCl solution in the flask, the solution would be colorless initially. When

just enough of the NaOH solution has been added to neutralize the HCl solution, the solution

would change to a pale pink.2 By measuring how much of the NaOH solution is needed to

neutralize the HCl solution, the concentration can be determined.

Experimental Section

A solution of HCl labeled as Unknown #159 was used in the experiment. Four 250-mL

Erlenmeyer flasks were labeled 1 through 4. Into each flask was added 25.00 mL of the HCl

solution, 50.0 mL of deionized water, two drops of phenolphthalein, and a magnetic stir bar.

A 50-mL buret was set up on a ring stand and filled with 0.1000 M NaOH. A magnetic stir

plate was set up under the buret. Flask 1 (serving as a rough trial) was placed on the stir plate

under the buret and titrated with the 0.1000 M NaOH until a faint pink color developed and

remained for 30 seconds. The volume of NaOH used in the rough trial was noted in order to

serve as a guide to obtaining a good endpoint for the other three trials. For each of the other

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three flasks, the NaOH was run in quickly until the volume added was about 1 mL less than

the volume used in the rough trial. Then for each flask, the NaOH was added drop-wise until

a faint pink color persisted for 30 seconds. The volume of NaOH used for each flask was

carefully noted and used to calculate the concentration of the HCl solution. The average

concentration (or mean), the deviation, and average deviation were also calculated. The true

value for the concentration of the HCl was provided and this value was used in the calculation

of the percent error.

Results and Discussion

The volume of 0.1000 M NaOH used for Trials 2, 3, and 4 were 35.28 mL, 35.20 mL, and

35.26 mL, respectively. The data and concentration results are summarized in the table

below.

Table: Data and Results for the Titration of HCl (#159) with 0.1000 M NaOH

Trial Rough # 2 #3 #4

Final Buret Reading (mL) 36.90 35.38 36.26 35.81

Initial Buret Reading (mL) 1.12 0.10 1.06 0.55

Volume of NaOH Dispensed (mL) 35.78 35.28 35.20 35.26

Concentration of HCl (M) 0.1411 0.1408 01.410

Deviation of Concentration (M) 0.0001 0.0002 0.0000

The range in the volume of NaOH used in the three good trials was 0.08 mL. For titrations

where the same amount of titrate is used, a range of less than 0.1 mL is indicative of good

precision.3

According to the balanced equation for the reaction, HCl and NaOH react in a 1:1 ratio.

HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)

Therefore, using the volume of NaOH reacted in each trial and the molarity of NaOH, the

molarity of HCl (Unknown #159) was calculated. The calculation of the HCl concentration

for Trial 2 is shown below.

35.28 mL NaOH( 1 𝐿

1000 𝑚𝐿 ) (

0.1000 𝑚𝑜𝑙 𝑁𝑎𝑂𝐻

1 𝐿 ) (

1

0.02500 𝐿 ) = 0.1411 𝑀

The concentrations calculated for Trial 3 and Trial 4 are done in a similar manner. The

average (or mean) concentration of HCl was found to be 0.1410 M. The deviation from the

mean for Trials 2, 3, and 4 are 0.0001 M, 0.0002 M, and 0.0000 M, respectively. The

calculation of the deviation from the mean for the concentration of HCl is calculated as

shown below for Trial 2.

Deviation from Mean = |experimental value  average value|

= |0.1411  0.1410| M = 0.0001 M

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The deviations in the concentrations for Trial 3 and Trial 4 are calculated in a similar manner.

The average deviation was found to be 0.0001 M, indicating that the result was very precise.

This is supported by the relative mean deviation (RMD) which is calculated to be 0.7 parts

per thousand. The calculation of the RMD is shown below.

Relative Average Deviation = 𝑎𝑣𝑒𝑟𝑎𝑔𝑒 𝑑𝑒𝑣𝑖𝑎𝑡𝑖𝑜𝑛

𝑎𝑣𝑒𝑟𝑎𝑔𝑒 𝑐𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 x 1000

= 0.0001 𝑀

0.1410 𝑀 x 1000 = 0.7 𝑝𝑝𝑡

An RMD of less than 1 part per thousand indicates good precision. And, although precision

and accuracy are not the same, good precision suggests good accuracy.

The only way to know the accuracy of the result is if the true value is known. If the true value

for the concentration of the HCl solution (Unknown #159) was 0.1452 M, the percent error in

the determination of the HCl concentration would be -2.9%. The percent error is calculated as

follows:

% error = 𝑎𝑣𝑒𝑟𝑎𝑔𝑒 𝑣𝑎𝑙𝑢𝑒−𝑡𝑟𝑢𝑒 𝑣𝑎𝑙𝑢𝑒

𝑡𝑟𝑢𝑒 𝑣𝑎𝑙𝑢𝑒 x 100

= 0.1410 𝑀−0.1452 𝑀

0.1452 𝑀 x 100 = −2.9%

The error calculation shows that the concentration of the HCl was less than the expected value.

The percent error of 2.9% shows that the accuracy was good, but could be improved upon.

The negative sign tells us that reported molarity is lower than the correct value. Perhaps the

error was due to the pipet used to deliver the HCl solution. It might not have been properly

calibrated. This would explain why the precision was excellent and yet the accuracy was not

as good as expected.

Conclusions The concentration of Unknown # 159 was determined to be 0.1411 M HCl, based on three

titration trials, with a relative average deviation of 0.7 parts per thousand and an error of

2.9%. The closeness of the experimental value (0.1411 M) to the true value (0.1452 M))

suggests that a simple acid-base titration is an effective method for finding the concentration

of an acid.

References 1. Yau, C. L. Chem 108 Experiments in Fundamentals of Chemistry Laboratory, 2nd Ed;

Academx: Baltimore, MD, 2007; pp 135-139.

2. Yau, C. CCBC-Catonsville, personal communication, 2015. 3. Poppins, M. J. Chem. Educ. 2017, 96, 23-29.

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