Lab Report

How to Write a Lab Report

A lab report is a document that explains the observations and conclusions drawn based on an experiment.  The Lab Report is written in the third person objective passive voice and contains a reasonable analysis of errors.  The point is to convey objective data. The third person subject is implied. No “You”, No “the researcher”, No people. This exercise will walk you through the parts of the lab report and what is expected throughout the course.


Title: Caffeine from Home Brewed Coffee – Drip vs French Press

One sentence or fragment describing the experiment.



This is where the thesis statement will be presented. The abstract is basically the TL;DR version of the lab. The abstract should contain:

  1. 1 sentence introduction to what was studied.
  2. 1-2 sentences summarizing the procedure
  3. 1-2 sentences with results
  4. 1 sentence conclusion
  5. 1 sentence offering what could skew the data. More on this in the discussion section of this assignment.

The abstract should be written after the experiment is complete.  This is written in the third person passive objective voice.


Caffeine was extracted from coffee brewed with the drip method and the French Press method. The coffee was brewed with distilled water heated to 88.0 oC. Contact time between the water and grounds was varied in one minute increments. After extraction with ethanol, the caffeine was collected and massed. It was found that coffee made with the French Press method at 88.0 oC with 3 minutes of contact time yielded the most caffeine per mL of coffee at 0.58mg/mL. This data may be skewed by extraction of other compounds preferentially soluble in ethanol. Further analysis will be concluded to determine statistical significance of the data and purity of the caffeine extracted.


Materials: (I don’t ask for this on the quiz)

A list or description of materials used.  (I’m totally making this up as I go so these materials are not necessarily needed for this exercise)

  • 50mL graduated cylinder
  • Coffee, cooled
  • Ethanol
  • Scale with 0.0001g precision (Analytical scale)
  • Sodium Chloride



Written in the third person, objective passive voice, the procedure provides the basics of what was done.

NOT: Take 50mL of coffee and salt it.  This is active voice.

NOT: A researcher obtained a 50mL sample of coffee. She then put salt in it.  This is 3rd person and passive but not objective. Objective = no people

NOT: Bart weighed out 5g of salt and mixed it into coffee. This is 3rd person and passive but not objective. Think of scientific writing as Magic. There are no people, it just happens. 

WRITE THIS INSTEAD: A 50mL room temperature coffee sample was mixed with approximately 5g of sodium chloride. The mixture was stirred to ensure complete mixing and allowed to sit for approximately 5 minutes.

You would continue this procedure to reflect the entire lab.



The results section contains tables of data, pictures (with your ID) of set up steps or results steps.  All numbers should have units or should have a key with what they mean (i.e. the time in the table below has mm:ss denoting that the numbers to the left of the colon are for the minutes and the numbers to the right are for the seconds.)  Your results would need to be complete for all of the data and observations made in the lab. I have only shown this table with the one set of conditions for illustrative purposes. Note: YOUR SCALE IS NOT THIS PRECISE. The Measurements and Precision lab will show you the precision of your lab ware.

For example:

Table 1: Results of French Press & 3 min contact
88.0 oC Distilled water + Jacob’s Ground Coffee Trial 1 Trial 2 Trial 3
Volume of water 250.0mL 250.0mL 250.0mL
Mass of coffee grounds 30.4067g 31.0245g 29.9901g
Contact time (mm:ss) 3:01 3:00 3:04
Mass of caffeine extracted 0.13mg 0.16mg 0.14mg



This is the most important part of the lab report. This is where you show your understanding of the experiment and the analysis of the results that were observed. Things to include in the discussion:

  1. Any chemical reaction that takes place (balanced of course – we’ll get there)
  2. Any calculations that were used (picture of handwritten is fine as long as it is big enough and clear enough to be seen with my old eyes)
  3. Lead me through the logical, scientifically sound progression of what was observed.
  4. Lead me to your conclusion.
  5. Evaluate errors in the data.

On Error:

NEVER STATE HUMAN ERROR it doesn’t exist. You can cause all sorts of errors, but those are Determinate errors. They are repeatable and correctable. It isn’t enough to say the data is skewed by determinate error… what is that determinate error. You don’t have to classify the error but explain what that error may cause in your observations.

For example: The caffeine extracted from the French Press method may be skewed by the natural fluctuations of caffeine content found within a bag of coffee. This error could be reduced by mixing the contents of a bag to ensure uniformity of grains. It is possible that all drip coffee values are skewed to the low side because of the flow through design of the method. The contact time variable may not have been as regulated as intended.

  • Errors are typically found in your assumptions.
    • For the above example, it is assumed that the caffeine is evenly distributed in the grounds in the coffee bag.
    • It is assumed that water contacting coffee grounds yields the extraction of caffeine. (mmm tasty)
    • It is assumed that there is a large enough sample size to gather general population data. (This is statistical – that’s my wheelhouse, so I had to leave this in)
    • It is assumed that a 3 minute contact time for French Press is the same as a 3 minute flow through time with the drip method (This is an experimental design flaw that may skew the French Press values upward and the drip method downward.)
    • It is assumed that the caffeine extraction from each cup of coffee is complete.  (This would skew the yield values downward)
    • It is assumed that there are no other compounds extracted with caffeine. (This would skew the yield values upward)
  • Uncertainty of a measurement is called experimental error.
    • Systematic
      • aka Determinate error. Repeatable. Often discovered and corrected.   i.e. I drank 2/3 of each French Press sample therefore didn’t have enough for adequate trials. Ok, we can fix that.
      • Incorrect standardization or calibration
    • Random
      • aka Indeterminate error. Natural fluctuations. Subjective interpretations.
      • Is this solution more blue or more green? Things that are hard to tell could be classified here as random error.
    • Precision vs. Accuracy
      • Precision is the reproducibility of a result. (This is discussed a bit in Module 1)
      • Accuracy is the how close the value is to “true”  (“true” is a statistical term)


State what was learned (not .. “I learned that…”) through the experiment. This is a statement like, “Coffee brewed with the French Press method yielded more caffeine per milliliter of coffee, 0.58mg/mL, than coffee brewed by the drip method, 0.45mg/mL.”  Notice how there is a declarative answer to the hypothesis with factual values. Nothing is vague in that conclusion sentence. Being vague isn’t science.  Let’s science. 😉



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