IB DP Chemistry Mock Exam HL Paper 1B Set 4 - 2025 Syllabus

(a)
• Weigh a known mass of the solid solute accurately on a balance (for example, mass \(m\) in \(\text{g}\)).
• Transfer the solid to a clean beaker and add a small volume of distilled / deionized water so that it dissolves completely (stir until all solid has dissolved).
• Quantitatively transfer the solution to a volumetric flask (rinsing the beaker and funnel and adding the washings to the flask).
• Add distilled water up to the calibration mark of the volumetric flask so that the total volume is exactly the stated volume (for example, \(250.0\ \text{cm}^3\)).
• Stopper the flask and invert / shake several times to ensure the solution is thoroughly mixed to give a uniform standard solution.
(No numerical calculations are required for this description.)

(b)
• Use the standard solution to prepare a series of solutions of different, accurately known concentrations by dilution (for example, using volumetric pipettes and volumetric flasks).
• For each of these solutions, measure the absorbance (or transmittance) with the colorimeter at a fixed wavelength using appropriate cuvettes.
• Plot a graph of absorbance (or transmittance) on the y-axis against concentration on the x-axis for all the solutions and draw a straight line of best fit (the calibration curve).
(Again, the process is qualitative; no numerical calculations are needed.)

(c)
• Measure the absorbance (or transmittance) of the unknown solution using the same colorimeter settings.
• On the calibration graph, locate this absorbance value on the y-axis, draw a horizontal line to the calibration line, then drop a vertical line to the x-axis to read the corresponding concentration of the unknown solution.
• Alternatively, use the equation of the straight line (for example, \(A = k c + b\)) to calculate the unknown concentration \(c\) from the measured absorbance \(A\).