Skip to content
Dabour HubLEARN · PRACTICE · EXPLORESign inStudent

Reactivity 3 — What are the mechanisms of chemical change?

Inquiry 2: Collecting and processing data — IB Chemistry SL Revision Notes & Topical Questions

10 min read 18 parts Lesson 10 of 12 Unit quiz

📚 IB Chemistry SL Hub / Topical Revision
🩺
100% Curriculum Specification Match Lesson Doctor Verified
The only platform with 100% curriculum specification match and verified interactive question banks.
0%read
Lesson summary

Inquiry 2: Processing data, uncertainties and presenting results — IB CHEMISTRY SL notes: Process raw chemistry data into averages and rates, propagate uncertainties and present results with correct significant figures and graphs.Raw data table — the first table, containing only …

  • Sufficient data
  • Qualitative data
  • Typical observations
  • Use as evidence
  • Issues during collection
  • Anomalous result

Part 1 of 8Recording raw data

Raw data table
  • Raw data table the first table, containing only direct measurements with no calculations.
Title
  • Title specific to the experiment.
Headers
  • Headers quantity, unit and uncertainty go in the column headings, not in each cell.
Precision
  • Precision record to the precision of the instrument, with the same decimal places in a whole column.
Burette
  • Burette readings to two decimal places, with the last digit 0 or 5, for example 24.50 cm3.
Balance
  • Balance a balance reading to two decimal places gives masses such as 5.00 g, never 5 g.
Sufficient data
  • Sufficient data at least five values of the independent variable, with at least three repeats of each.

Part 2 of 8Qualitative observations

Qualitative data
  • Qualitative data non-numerical observations recorded alongside the numbers.
Typical observations
  • Typical observations colour changes, effervescence, formation of a precipitate, soot during combustion and noticeable temperature changes.
Use as evidence
  • Use as evidence observations help explain unexpected results and errors in the analysis and evaluation.
Issues during collection
  • Issues during collection record problems such as a reaction that is too fast or slow, or a gradual endpoint.
Anomalous result
  • Anomalous result record it, do a further trial to get concordant results, and do not erase it.
  • Its exclusion is justified later.

Part 3 of 8Processing raw data

1Processed data
  • Processed data new, clearly labelled table separate from the raw data.
2Working
  • Working show one full set of working for each type of calculation, even if a spreadsheet is used.
3Units
  • Units every calculated value has correct units, and a new quantity such as a rate needs derived units (for example s−1 or mol dm−3 s−1).
1
Average the repeat trials, leaving out any justified anomalous result.
2
Calculate the quantity of interest, for example rate = 1 / time.
3
Propagate the uncertainty through each calculation.
4
Round the final value to a suitable number of significant figures.

Part 4 of 8Averages in titrations

Concordant titres
  • Concordant titres only titres within 0.10 cm3 of each other are averaged.
Rough titre
  • Rough titre always excluded from the average.
Anomalous titres
  • Anomalous titres excluded as well.
Titre
  • Titre final burette reading minus initial burette reading.
Dilution
  • Dilution if the sample was diluted, multiply the calculated concentration by the dilution factor.

Part 5 of 8Propagating uncertainty

1Addition or subtraction
  • Addition or subtraction add the absolute uncertainties.
  • A titre uses two burette readings, so the uncertainty is 0.05 + 0.05 = 0.10 cm3.
2Multiplication or division
  • Multiplication or division add the percentage uncertainties.
  • For n = C × V, the percentage uncertainty in n is that in C plus that in V.
3Reciprocal
  • Reciprocal for rate = 1 / t, the percentage uncertainty in the rate equals the percentage uncertainty in time.
4Powers (HL)
  • Powers (HL) multiply the percentage uncertainty by the power.
5Final uncertainty
  • Final uncertainty quote it to one significant figure and give the result to the same number of decimal places.
6Sample calculation
  • Sample calculation show the propagation for the main processed result.

Part 6 of 8Significant figures in processed results

1Rule
  • Rule the final answer has the same number of significant figures as the least precise data used.
2Calculator display
  • Calculator display never write down the full display.
3Constants
  • Constants a constant such as the Avogadro constant is used with its defined number of significant figures and does not limit precision.
4Intermediate values
  • Intermediate values keep the calculator value until the final answer to avoid rounding errors.

Part 7 of 8Presenting results as a graph

Presenting results as a graph
Title
  • Title describes the relationship investigated.
Axes
  • Axes independent variable on x, dependent variable on y, with quantities and units.
Scale
  • Scale appropriate, linear, and using at least half of the space.
Points
  • Points clearly plotted, usually as a small x or a point in a circle.
Line of best fit
  • Line of best fit a smooth line or curve showing the overall trend, with about equal numbers of points on each side.
Gradient
  • Gradient can represent a key value, for example the rate constant k from a rate against concentration graph for a first-order reaction.
Intercept
  • Intercept the value of the dependent variable when the independent variable is zero.
Area under a curve
  • Area under a curve a total quantity such as the number of particles in a Maxwell–Boltzmann curve.
Error bars
  • Error bars their size shows precision, and large bars suggest significant random error.

Part 8 of 8More from the specification

1Quantitative Data Collection and Experimental Accuracy
  • In scientific chemistry inquiry, gathering sufficient quantitative raw data with high measurement accuracy is essential to answer a focused research question reliably.
2Disappearing Cross Experiment with Sodium Thiosulfate
  • In reaction kinetics investigations, the reaction between sodium thiosulfate and hydrochloric acid produces a cloudy sulfur precipitate;
    • timing how long it takes for a black cross to disappear allows quantitative rate analysis.
3Acid-Base Titration of Commercial Vinegar
  • Determining the concentration of ethanoic acid in household vinegar involves volumetric titration with standard sodium hydroxide solution, calculating mean concordant titres for rigorous data interpretation.
4Scientific Interpretation of Experimental Results
  • Interpreting results requires analyzing graphs, identifying anomalous data points, calculating percentage errors,
  • and formulating evidence-based scientific conclusions that evaluate methodological validity.
5Vinegar
  • An ethanoic acid solution of about 5%.
6Accuracy
  • Closeness of a result to the true value.

Key terms

TermMeaning
Raw dataMeasurements exactly as recorded from the instrument.
Processed dataRaw data after calculation, such as averages and rates.
Propagated uncertaintyUncertainty in a calculated result found by combining the uncertainties of the measured values.
Significant figuresMeaningful digits in a number, set by the least precise measurement.
Concordant titresTitres within 0.10 cm3 of each other.
Error barA bar on a graph point showing its uncertainty.
Anomalous resultA value clearly outside the pattern of the other repeats.
InterceptThe point where a line crosses an axis.

Avoid these mistakes

1
Quoting final answers with more significant figures than the least precise data allow.
2
Adding absolute uncertainties when multiplying — percentage uncertainties are added for multiplication and division.
3
Omitting units for calculated quantities such as rate.
4
Removing an anomalous result without stating the reason.
5
Recording raw data to the wrong number of decimal places for the instrument.

Last updated:

\n