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

Section 1 of 18Recording 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.

Section 2 of 18Qualitative 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.

Section 3 of 18Processing 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.

Section 4 of 18Averages 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.

Section 5 of 18Propagating 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.

Section 6 of 18Significant 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.

Section 7 of 18Presenting 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.

Section 8 of 18More 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.

Section 9 of 18Interpreting a graph

1Aim

• Aim find what the results tell you so that the research question can be answered.

2Two steps

• Two steps first describe the trend, then explain it with chemical principles.

3Describing

• Describing use terms such as linear positive correlation, inversely proportional, exponential increase and the rate plateaus.

4Explaining

• Explaining link the trend to theory such as collision theory or intermolecular forces;
  • this is the most important part.

5Use data

• Use data a description should quote values from the data.

Section 10 of 18Explaining the effect of temperature on rate

1Trend

• Trend rate increases non-linearly with temperature, rising at an accelerating pace.

2Higher kinetic energy

• Higher kinetic energy raising temperature increases the average kinetic energy of the particles.

3More frequent collisions

• More frequent collisions the particles move faster.

4More successful collisions

• More successful collisions a much greater proportion of particles have at least the activation energy, and this is the main reason for the steep rise.

Section 11 of 18Anomalous results

Definition

• Definition an anomalous result is a point that clearly does not fit the overall trend.

Showing it

• Showing it highlight it on the graph.

Justifying it

• Justifying it link it to a likely experimental error, such as a delay in starting a stopwatch.

Handling

• Handling it is excluded from the average and the graph with the reason stated.

Section 12 of 18Qualitative and quantitative data together

Qualitative evidence

• Qualitative evidence observations help explain quantitative results.

Soot

• Soot black soot on a calorimeter shows incomplete combustion, which releases less energy.

Effect

• Effect an enthalpy of combustion lower in magnitude than the data booklet value can be explained by this observation.

Section 13 of 18Accuracy and precision

Idea	Meaning	Affected by
Accuracy	How close the final result is to the accepted or true value	Systematic errors
Precision	How close repeat measurements are to each other	Random errors

1Accuracy needs a literature value

• Accuracy needs a literature value it can only be commented on when one exists.

2Precise but inaccurate

• Precise but inaccurate a small spread of repeats does not prove accuracy;
  • a systematic error gives precise but wrong results.

Section 14 of 18Reliability and validity

Reliability

• Reliability the consistency of results; several concordant repeats make results reliable.

Validity

• Validity relates to the method;
  • results are valid if it was a fair test with significant variables controlled.

Spread of repeats

• Spread of repeats the range or half-range gives a practical estimate of random uncertainty.

Reporting

• Reporting quote the final value with its uncertainty and say whether the spread of repeats supports it.

Cautious conclusions

• Cautious conclusions a large percentage uncertainty tells the reader the conclusion must be cautious.

Section 15 of 18Random and systematic error

Error type	Effect on data	How to reduce it
Random	Scatter around the true value; affects precision	Repeat trials and average; use a better instrument
Systematic	Shifts all results the same way; affects accuracy	Calibrate the instrument, change the method, correct for heat loss

Section 16 of 18More from the specification

1

Data collection with a burette

• During acid-base titration experiments, initial and final burette readings are recorded to two decimal places, calculating the titre as the difference between readings.

2

Concordant titres and data processing

• Processing experimental data involves identifying concordant titre values to calculate a mean titre, discarding non-concordant outliers.
  • (readings within 0.10 cm³ of each other)

3

Calculating unknown concentrations

• Processed stoichiometric data allows determination of the unknown concentration of analyte solutions using balanced reaction ratios (n = c * V) with correct scientific units (mol dm^-3.

4

Evaluating independent variables in kinetics

• In chemical kinetics, systematically varying the independent reactant concentration while measuring reaction times produces processed rate data expressed in scientific notation.

5

Data collection with a burette

• During acid-base titration experiments, initial and final burette readings are recorded to two decimal places, calculating the titre as the difference between readings.

6

Concordant titres and data processing

• Processing experimental data involves identifying concordant titre values to calculate a mean titre, discarding non-concordant outliers.
  • (readings within 0.10 cm³ of each other)

7

Calculating unknown concentrations

• Processed stoichiometric data allows determination of the unknown concentration of analyte solutions using balanced reaction ratios (n = c * V) with correct scientific units (mol dm^-3.
  What the symbols mean: c = concentration (mol dm⁻³) · n = amount (mol) · V = volume (dm³; divide cm³ by 1000)

8

Evaluating independent variables in kinetics

• In chemical kinetics, systematically varying the independent reactant concentration while measuring reaction times produces processed rate data expressed in scientific notation.

9

Independent variable

• The variable that is changed.

10

Significant figures

• The digits in a value that are reliable and carry meaning.

11

Dependent variable

• The variable that is measured.

12

Concentration

• Moles ÷ volume in dm³, or g/dm³.

13

Burette

• Apparatus delivering a variable volume accurately, 0-50 cm³.

14

Vinegar

• An ethanoic acid solution of about 5%.

Section 17 of 18Key terms

Term	Meaning
Raw data	Measurements exactly as recorded from the instrument.
Processed data	Raw data after calculation, such as averages and rates.
Propagated uncertainty	Uncertainty in a calculated result found by combining the uncertainties of the measured values.
Significant figures	Meaningful digits in a number, set by the least precise measurement.
Concordant titres	Titres within 0.10 cm3 of each other.
Error bar	A bar on a graph point showing its uncertainty.
Anomalous result	A value clearly outside the pattern of the other repeats.
Intercept	The point where a line crosses an axis.

Term	Meaning
Accuracy	How close a result is to the accepted value.
Precision	How close repeated measurements are to each other.
Reliability	How consistent repeat results are.
Validity	Whether the method measures what it is meant to, with variables controlled.
Collision theory	Reactions occur when particles collide with enough energy and correct orientation.
Activation energy	The minimum energy particles need for a successful collision.
Anomalous result	A data point that does not fit the overall trend.

Section 18 of 18Exam technique

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.

1

Commenting on accuracy without a literature value to compare with.

2

Confusing precision with accuracy — precise results can still be inaccurate if there is a systematic error.

3

Explaining the temperature effect only by more frequent collisions — the larger proportion of particles with at least the activation energy is the major factor.

4

Describing a graph without quoting any data from it.