Lab Reports

A Lab Report is REQUIRED for each experiment.

A Lab Report grading rubric will be provided. 

Lab Report Format:

All lab reports must be typewritten and saved in Rich Text Format.  

Each Lab Report should begin with the following information in the upper left hand corner:

Title
Exp. No.
Name
Date
 
 
Followed by...
 
 I.   Purpose
II.   Experimental Method
III.  Raw Data and Calculations
IV.  Results
V.   Conclusion

Use Roman Numerals and Section Headings, as listed above, in ALL of your reports.   Here is more information about each section.

Purpose

A statement of objectives or a hypothesis may be necessary in this section. The hypothesis is what you think will happen during the investigation. It differs from a guess in that it is based upon prior knowledge or evidence. If an hypothesis is stated it should be supported by previously developed evidence and/or concepts.

Experimental Method

Describe materials/equipment used.  Write a summary of the procedure. DO NOT copy the procedure given in your experiment handout or write a step-by-step list of the method.   Instead, summarize the procedure.   Explain what you did in order to collect the DATA. You should understand and be able to apply the principles involved in running the experiment.  And you are encouraged to identify the assumptions upon which the experiment is based.

Raw Data and Calculations

Evidence collected during the experiment; numbers read directly from laboratory instruments (clocks, rulers, balances, etc., but not calculators). Data should be well organized and tabulated when possible. Use care in scale reading and use significant figures when taking measurements. Develop a sense of how much data is desirable. Do not hide or eliminate suspected faulty data but present it. Later, in your CONCLUSIONS, you may explain why you have decided not to use suspected errors in your analysis.

Other forms of evidence, qualitative in nature, may also be recorded in this section; for example, something unexpected that happened during the experiment that may affect your CONCLUSIONS.  Observations such as color changes, precipitate formation, gas evolution should also be recorded.

Show all calculations.  You are encouraged to use calculators and computers. Spreadsheet graphs used in the analysis should appear in this section. Use significant figures in calculations involving measurements. Use units as well as numbers in all calculations. Use dimensional analysis to accomplish this.

Results

The final form in which the evidence is prepared. You perform CALCULATIONS on the DATA in order to develop RESULTS. Your CONCLUSIONS should be understandable by looking at your RESULTS. Tables, and graphs are appropriate in this section.  Do Not show calculations in this section.

Conclusion

This section contains the answers to the problem stated in the TITLE and INTRODUCTION. Base your conclusions on your RESULTS, not despite them. Look for more than one conclusion to the problem, with suggestions for further work in order to differentiate these at a later date. It is not necessary to do the further work. Understand that conclusions from one experiment usually form the hypotheses to new experiments. Explain experimental errors that appear in the results. Show an awareness of the limitations of the results when making generalizations.


How and Where to Submit your Lab Reports

Lab Reports will be submitted electronically to a designated location in our course website.  Instructions will be provided.

It is your responsibility to keep a copy of each lab report in case your report is lost in cyberspace.


Lab Report Sample

Use this sample lab report as a guide to help you write your own lab reports.

Determination of Acetic Acid in Vinegar
Exp. No. 14
Albert Einstein
March 5, 1998

I.  Purpose

The purpose of this experiment was to determine the percentage of acetic acid (CH3COOH) in a commercial vinegar sample.  Acetic acid is monoprotic and belongs to the carboxyl family of organic compounds.  It reacts with bases such as NaOH to form a salt and water. The balanced chemical equation for the neutralization of acetic acid with NaOH is:

CH3COOH   +   NaOH   --->   CH3COONa    +   H2O

The equivalence point of this neutralization reaction can be determined using a chemical indicator to signal the endpoint.

II.  Experimental Method

Equipment:  125 mL Erlenmeyer Flasks, two 50 mL burets, buret stand and clamp

Chemicals:   0.1 M NaOH, Phenolphthalein Indicator, Commercial Vinegar

The vinegar sample was titrated with standardized sodium hydroxide solution (0.1M NaOH).  A measured sample of vinegar was placed under a buret.  The buret was filled with the standardized NaOH solution.  A chemical indicator, phenophthalein,   was added to the vinegar solution to allow the endpoint of the neutralization to be detected.  The initial volume of the buret was read and recorded before beginning the titration.  The titration was performed drop-by-drop until the indicator changed color.  At the endpoint, the final volume of  NaOH solution was read and recorded.  Using the volume and molarity of NaOH, and the volume and density of vinegar, the percentage of acetic acid in the sample was calculated (see calculation section for calculation methods used in this experiment).

III.  Raw Data and Calculations

Data Section:

Initial Vinegar Buret Reading     0.09 mL
Final Vinegar Buret Reading    20.09 mL
Volume of Vinegar Used         20.00 mL
Initial NaOH Buret Reading       0.19 mL
Final NaOH Buret Reading     23.60 mL
Volume of NaOH Used          23.41 mL
Density of Vinegar                    1.01 g/mL
Molarity of NaOH                   0.595 M
True Value of CH3COOH in Vinegar  =  4.00%

Calculation Section:

Moles NaOH = Volume x Molarity
Moles NaOH = = 23.41 mL x 0.595mol/1000 mL = 0.0139 moles
Moles CH3COOH  =  0.0139 moles NaOH x (1mol CH3COOH/1 mol NaOH)
Moles CH3COOH  = 0.0139 moles
Mass of CH3COOH  =  0.0139 moles  x  (60.0 g/mole)  =   0.834 grams
Mass of Vinegar Sample  =  Density x Volume
Mass of Vinegar Sample  =  1.01 g/mL  x  20.00 mL  =   20.2 grams
% CH3COOH in Vinegar  =  ((mass of CH3COOH)/(mass of Vinegar)) x   100
% CH3COOH in Vinegar  =  (0.834g/20.2 g)  x  100  =   4.13 %
% Error  = ( (|true - observed|)/true)  x  100
% Error  =  (|4.00-4.13|)/4.00   x   100    =  3.25 %

IV.  Results

grams CH3COOH 0.834 grams
grams Vinegar 20.2 grams
Experimental % CH3COOH 4.13 %
True % CH3COOH 4.00 %
% Error 3.25 %

V.  Conclusion

The purpose of this experiment was to determine the percentage of acetic acid, CH3COOH, in a commercial vinegar sample.  The percentage of CH3COOH was found to be 4.13 %.  The true value from the label on the commercial vinegar sample label was 4.00 %.  The deviation of the experimental value from the true value was calculated to be 0.13.  Using the true value and experimental value, a percent error was calculated.  The percent error was found to be 3.25 %. 

The experimental percentage of CH3COOH in the vinegar sample is higher than the true value.  One possible source of error to account for this discrepancy could be titration past the true equivalence point of the reaction.  Addition of more NaOH than required to reach the end point would give a larger value for the number of moles of NaOH used.  An error in the moles of NaOH used would result in a larger value for the number of moles of CH3COOH in the sample.  A larger number for the moles of CH3COOH would result in a larger mass of CH3COOH in the sample.  The larger mass of acetic acid would result in a higher percentage of acid in the sample. 

One suggestion to improve the results of this experiment would be titrate 3 samples of the same vinegar sample and average the results. 

 

Michael W.  McClure
Professor, Chemistry
Hopkinsville Community College
Phone:  270-886-3921

Copyright 1999  M.W. McClure, All Rights Reserved

No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form, by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of the publisher.