Data Analysis and Graph Questions

Data analysis questions test your ability to extract information from graphs, tables, and experimental results. These questions appear in all three papers and carry significant marks.

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Reading Graphs Accurately

Rate-Concentration Graphs

When given a concentration-time graph, the rate at any point is the gradient of the tangent at that point. To find the initial rate, draw a tangent at t = 0. Common errors include drawing the tangent too steeply or too shallowly, or measuring the gradient incorrectly.

To find the gradient:

1. Draw the tangent line (touching the curve at the required point)
2. Choose two points on the tangent line that are far apart
3. Calculate Δy / Δx using these points
4. Include units (typically mol dm⁻³ s⁻¹)

Titration Curves

Titration curves show pH against volume of titrant added. Key features to identify:

• Equivalence point — the steepest part of the curve (where pH changes most rapidly)
• Half-equivalence point — halfway to the equivalence point, where pH = pKa for a weak acid
• Buffer region — the relatively flat section before the equivalence point
• Initial pH — indicates whether the analyte is a strong or weak acid/base