How to Write a Chemistry Lab Report

The title page is the first thing your reader sees, and its purpose is simple: to identify the experiment, the author(s), the course, and the date clearly and completely. A well-constructed title page contains: the experiment title (the most important element), the student’s name and partner(s) if applicable, the course name and number, the instructor’s name, the institution, and the date the experiment was performed and/or the date the report was submitted. Follow your instructor’s specific formatting requirements — some courses provide a title page template.

The experiment title deserves more thought than it typically receives. A good title is specific, informative, and directly descriptive of what the experiment measured or determined. It should contain enough information that a reader understands the nature and scope of the experiment without reading further. Avoid vague titles like “Experiment 3” or overly generic titles like “Acid-Base Reactions.” Strong chemistry experiment titles typically identify the measurement or determination being made and the chemical system it was applied to.

Determination of the Empirical Formula of a Copper Chloride Hydrate
by Gravimetric Analysis

Student Name:       Sarah Chen
Lab Partner:        Marcus Webb
Course:             CHEM 2250 — Quantitative Analytical Chemistry
Instructor:         Dr. A. Okonkwo
Institution:        University of Nairobi, Department of Chemistry
Date Performed:     March 15, 2026
Date Submitted:     March 22, 2026

The Abstract is a concise, self-contained summary of the entire laboratory report — typically 150 to 250 words — that allows a reader to understand the essential purpose, methods, key results, and conclusions of the experiment without reading the full report. It is the most read section of any scientific document (many readers decide whether to read further based solely on the abstract), and it is the last section you should write, because it can only accurately summarise a report that has been completely written.

A well-structured chemistry lab report abstract covers five elements in sequence: (1) Purpose — what the experiment investigated or determined; (2) Methods — the key technique(s) used, in one or two sentences; (3) Key Results — the most important quantitative findings, including units; (4) Percent Error or Comparison to Theory — how closely results matched accepted values; (5) Conclusion — what the results demonstrate about the underlying chemistry. Everything in the abstract must be reflected in the full report — the abstract is a summary, not a teaser. It contains no information not present in the report, no figures, no citations (in most formats), and no speculation beyond what the data supports.

The Introduction section establishes the theoretical and scientific context for the experiment, explains what the experiment was designed to investigate or determine, and states the specific objectives or hypotheses the experiment tests. It moves from general background (the relevant chemistry principles, reactions, or methods) to the specific (what this particular experiment does and why). A strong Introduction answers the question a scientifically literate reader would ask before reading the rest of the report: why should I care about this experiment, and what is it testing?

The Introduction is written in the present tense for established scientific facts and theoretical principles (“Beer’s Law states that absorbance is directly proportional to concentration…”) and in the past tense for previous experimental work you are referencing (“Smith et al. (2018) demonstrated that…”). It should include: the relevant chemical reactions written in balanced equation form; the key theoretical principles underlying the experiment; the significance or practical application of the measurement or synthesis being performed; any relevant literature values you will compare your results to; and a clear statement of the experimental objectives. It should not include your results, your procedure, or any information that belongs in another section.

What to Include in the Introduction

The Materials and Methods section — also called the Experimental Procedure or Experimental section — provides a complete, reproducible description of how the experiment was performed. Its primary purpose is to allow another competent chemist to replicate your experiment exactly, and to evaluate the quality and reliability of your results based on the methods you used. Every aspect of the procedure that could affect your results — reagent concentrations, volumes, masses, equipment specifications, timing, temperature, mixing order, and analytical instrument settings — should be recorded. What should not appear in this section is anything about your results or conclusions — those belong in the Results and Discussion sections respectively.

The Two Non-Negotiable Conventions: Passive Voice and Past Tense

The Experimental section is written in the past tense passive voice — not because this is an arbitrary stylistic convention but because it reflects the philosophy of objective scientific reporting. The passive voice removes the personal agent (“I”) from the description of the experiment, framing the procedure as something that was done to the materials rather than something a specific person chose to do. This framing emphasises the reproducibility of the method — in principle, anyone following the same procedure would obtain the same results, independent of the particular researcher. The convention is universal in published chemistry literature and is expected at all academic levels above high school.

What to Include in Materials and Methods

The Experimental section should include: a complete materials list (reagents with concentrations, grades, and sources; glassware and equipment with capacities and specifications; instruments with manufacturer, model, and calibration details where relevant); and the procedure itself, written as a coherent narrative or organised set of numbered steps that completely describes what was done. Every significant procedural choice — why a particular solvent was used, why a specific temperature was chosen, why a particular indicator was selected — should be briefly justified if it is not self-evident from the context.

A critical and frequently missed requirement is the distinction between the written procedure (what the lab manual says to do) and the actual procedure (what you actually did). Your lab report must describe what you actually did, including any deviations from the written procedure, any anomalies in the process, and the actual values of measured quantities used — not the nominal values in the protocol. If the protocol says “add approximately 5 mL” but you added 5.13 mL, your report should record 5.13 mL.

The Results section presents your experimental data — all of it, organised clearly and completely — together with the calculations performed on that data. It does not interpret or explain the data — that is the function of the Discussion section. The distinction between reporting results (what was found) and interpreting results (what it means and why) is one of the most important conventions in scientific writing, and maintaining it clearly is a consistent marker of quality in assessed lab reports.

The Results section consists of three principal elements: data tables, figures and graphs, and sample calculations. Each element has specific formatting conventions that must be followed for the section to be professionally presented.

Data Tables: Format and Conventions

Data tables present your raw and processed data in an organised, readable format. Every table in a chemistry lab report must have: a numbered title above the table (e.g., “Table 1. Titration Data for the Determination of Acetic Acid in Vinegar”); column headers that include the quantity name and the unit in parentheses or using the slash notation (e.g., “Volume / mL” or “Volume (mL)”); all data presented to the appropriate number of significant figures; a clear distinction between raw data (measured directly) and derived data (calculated); and all measurements recorded with consistent precision (all burette readings to two decimal places, for example, regardless of the leading digit).

Sample Calculations: Showing Your Work

The Results section must include sample calculations — clearly presented, step-by-step examples of every distinct type of calculation performed. For a titration experiment, this would include at minimum: the calculation of moles of titrant used, the calculation of moles of analyte from stoichiometry, and the calculation of analyte concentration. Each calculation should show: the formula used, with variable definitions; the substitution of values with units; and the final numerical result with appropriate units and significant figures. Showing sample calculations for one trial set is standard — you do not need to show all four sets individually, but all final results should appear in the results table.

Step 1: Moles of NaOH used at equivalence point
  n(NaOH) = c(NaOH) × V(NaOH)
  n(NaOH) = 0.09876 mol L⁻¹ × 0.02292 L
  n(NaOH) = 2.263 × 10⁻³ mol

Step 2: Moles of CH₃COOH (1:1 stoichiometry with NaOH)
  CH₃COOH + NaOH → CH₃COONa + H₂O
  n(CH₃COOH) = n(NaOH) = 2.263 × 10⁻³ mol

Step 3: Molar concentration of acetic acid in vinegar
  c(CH₃COOH) = n / V(vinegar)
  c(CH₃COOH) = 2.263 × 10⁻³ mol / 0.02500 L
  c(CH₃COOH) = 0.09052 mol L⁻¹

Step 4: Mass percentage of acetic acid (MM = 60.05 g mol⁻¹)
  mass / L = 0.09052 mol L⁻¹ × 60.05 g mol⁻¹ = 5.437 g L⁻¹
  mass% = (5.437 g / 1000 mL) × 100% = 0.5437% ≈ 5.44% w/v

Graphs and Figures: Scientific Plotting Conventions

Any graph or figure included in the Results section must meet professional scientific plotting standards. Every figure must have: a numbered caption below the figure (“Figure 1. Calibration curve for iron determination by spectrophotometry at λ = 510 nm”); labelled axes with quantity names and units; clearly legible data points with appropriate error bars where statistical analysis has been performed; a best-fit line or curve (not a dot-to-dot line connecting experimental points) where the relationship is linear or follows a known function; and a statement of the equation of the line and R² value for linear regression plots. Graphs should be plotted with the independent variable on the x-axis and the dependent variable on the y-axis. Use appropriate axis scales — axes should not start at zero if this compresses all your data into a small corner of the plot.

Significant Figures: The Most Consistently Marked Convention

Significant figures are one of the most consistently marked elements of chemistry lab reports, and errors in significant figure reporting are among the most common sources of mark deductions at undergraduate level. The rules are as follows. Retain as many significant figures in your calculations as your least precise measurement allows. Report final calculated results to the same number of significant figures as the measurement with the fewest significant figures that contributed to the calculation. In data tables, report all values for the same measurement to the same number of decimal places (consistency within columns). Never report more significant figures than your measuring instrument can provide — a balance reading to 0.001 g cannot produce a mass value like 5.67893 g. When multiplying and dividing, the result has as many significant figures as the factor with the fewest. When adding and subtracting, the result has as many decimal places as the value with the fewest decimal places.

The Discussion section is simultaneously the most important and most commonly weak section in undergraduate chemistry lab reports. It is where you demonstrate genuine scientific understanding — not just procedural competence — by interpreting your results, comparing them to expected values, analyzing sources of error rigorously, and drawing evidence-based conclusions. A Results section that simply presents the data is complete; a Discussion that merely describes what the Results section showed is not. The Discussion must go beyond the data to explain it, evaluate it, and contextualise it within the theoretical framework of the experiment.

The Discussion should address five interconnected analytical tasks: (1) Interpret your results — what do your numerical findings mean in terms of the chemical system you studied?; (2) Compare to accepted/theoretical values — calculate percent error and evaluate whether your results are accurate; (3) Analyze sources of error — identify specific, named sources of error and explain how each would have affected your results in which direction; (4) Explain anomalies — address any unexpected results or outliers with a scientifically plausible explanation; (5) Evaluate the method — assess the suitability of the experimental method for the purpose, and suggest specific improvements.

How to Write a Strong Percent Error Discussion

The percent error calculation is the numerical anchor of the Discussion section — it quantifies the discrepancy between your experimental finding and the established reference value and provides the starting point for error analysis. But the calculation alone is not enough. The Discussion must: state the percent error value; characterise whether this error is acceptable for the method used (a 0.5% error in a titration experiment is excellent; a 0.5% error in a gravimetric experiment might indicate a significant problem; a 5% error in a calorimetry experiment is reasonably good); and systematically explain which specific sources of error contributed to the discrepancy and whether each would have driven your result high or low relative to the accepted value.

Notice the analytical features of that example: it states the specific percent error value; characterises its magnitude relative to what would be expected for the method; identifies a specific, mechanistically explained source of systematic error rather than vague claims like “human error”; explains the direction of that error’s effect on the result; confirms that the direction is consistent with the observed discrepancy; and proposes specific improvements. This is the analytical depth that distinguishes a high-quality Discussion from a generic one.

Writing About Sources of Error: What “Human Error” Is Not

The phrase “human error” is one of the most common and most consistently penalised statements in chemistry lab reports. It is not an error analysis — it is a non-explanation. Every experimental result that deviates from theory was collected by humans; saying the deviation is due to “human error” conveys no information about the specific mechanism of that error, its likely magnitude, or its direction. The Discussion section requires specific, named, mechanistically explained sources of error. Instead of “human error in measuring volumes,” write “systematic over-reading of the burette meniscus — reading from above rather than at eye level to the bottom of the meniscus — which would consistently result in volumes being read as larger than their actual value, causing calculated concentrations to be underestimated.” That is an error analysis. The former is a placeholder that earns zero analytical marks.

Common Discussion Mistakes to Avoid

The Conclusion section provides a concise synthesis of the experiment’s findings and their significance. It is typically the shortest substantive section of the report — 150 to 300 words for a standard undergraduate experiment — and its purpose is distinct from the Discussion. Where the Discussion is analytical and exploratory (interpreting results, analyzing errors, evaluating the method), the Conclusion is synthetic and declarative: it states clearly what the experiment found, whether the experimental objectives were achieved, what the results demonstrate about the underlying chemistry, and what broader implications or future directions the work suggests.

The Conclusion should: restate the main result quantitatively (not just “the concentration was determined” but “the concentration was determined to be 0.09052 ± 0.00008 mol L⁻¹”); state whether the objectives were achieved; briefly acknowledge the primary sources of error and their effect on result quality (without repeating the full error analysis from the Discussion); and state the broader significance or application of the finding. The Conclusion should not introduce new data, new references, or new arguments that have not appeared elsewhere in the report — it synthesises what has already been established, not what remains to be discovered.

The References section lists all sources cited in the report. Every claim in the report that draws on established knowledge — every literature value, every theoretical principle, every cited study — must be supported by an in-text citation and a corresponding reference list entry. Chemistry lab reports most commonly use American Chemical Society (ACS) citation style, which uses superscript numerals in-text and numbered reference list entries in order of first citation. Some institutions use APA or another style — always follow your course guidelines.

Appropriate sources for chemistry lab reports include: peer-reviewed journal articles accessed through databases such as Web of Science, SciFinder, or ACS Publications; standard reference texts such as the CRC Handbook of Chemistry and Physics (for physical and chemical property data); undergraduate analytical or physical chemistry textbooks (Skoog, Atkins, Harris, etc.) for theoretical background; the NIST Chemistry WebBook for thermodynamic and spectroscopic data; and your institution’s laboratory manual. Inappropriate sources include Wikipedia, non-peer-reviewed websites, and any source whose authorship or accuracy you cannot verify. If your report cites a number from the internet, ask yourself: was this verified by a peer-review process? If not, find the primary source.

(1)  Skoog, D. A.; West, D. M.; Holler, F. J.; Crouch, S. R. Fundamentals of
     Analytical Chemistry, 9th ed.; Brooks/Cole, Cengage Learning: Belmont, CA, 2014.

(2)  Harris, D. C. Quantitative Chemical Analysis, 10th ed.; W. H. Freeman:
     New York, 2020; pp 245–267.

(3)  Haynes, W. M., Ed. CRC Handbook of Chemistry and Physics, 103rd ed.;
     CRC Press/Taylor & Francis: Boca Raton, FL, 2022.

(4)  Atkins, P.; de Paula, J.; Keeler, J. Physical Chemistry, 11th ed.;
     Oxford University Press: Oxford, UK, 2023.

(5)  NIST Chemistry WebBook. Standard Reference Database 69; National Institute
     of Standards and Technology: Gaithersburg, MD. https://webbook.nist.gov
     (accessed March 15, 2026).