IB DP Chemistry Mock Exam SL Paper 1B Set 5 - 2025 Syllabus

(a)
To prepare a standard aqueous solution:

1. Accurately weigh a known mass of the solid solute using a balance.
2. Dissolve the solid completely in a small volume of distilled or deionized water.
3. Transfer the solution quantitatively to a volumetric flask.
4. Add more distilled/deionized water to the flask until the bottom of the meniscus reaches the calibration mark on the neck of the flask.
5. Stopper the flask and invert it several times to ensure thorough mixing.

Any three of the above steps.

(b)
To construct a calibration curve:

1. Prepare a series of standard solutions with different, known concentrations (e.g., by dilution).
2. Use the colorimeter to measure the absorbance (or transmittance) of each standard solution.
3. Plot a graph of absorbance (on the y-axis) against concentration (on the x-axis).
4. Draw a line of best fit through the data points.

\(\boxed{\text{Measure absorbance vs concentration and plot graph}}\)

(c)
The absorbance of the unknown sample is measured using the same colorimeter. This absorbance value is then located on the y-axis of the calibration curve. A horizontal line is drawn from this point to the line of best fit, and then a vertical line is dropped down to the x-axis to read the corresponding concentration. \(\boxed{\text{Measure unknown’s absorbance and read concentration from graph}}\)