IB Chemistry IA idea · Rates of reaction
IB Chemistry IA idea: how fast does bleach fade a food dye?
A drop of bleach drains the colour from a food dye in a way that a colorimeter can time exactly.
These ideas are starting points, not an IA to copy. Never copy an idea blindly: make the question, method and analysis your own, and check your plan with your teacher.
Example research question
How does the concentration of diluted sodium chlorate(I) (0.001, 0.003, 0.005, 0.008 and 0.010 mol dm⁻³) affect the pseudo-first-order rate constant (s⁻¹) for fading of brilliant blue, from absorbance in a colorimeter?
Change the system, the range or the method so the question is yours. Check it against the research question checklist in our Chemistry IA guide.
Variables
- You change
- Concentration of diluted sodium chlorate(I) (bleach), for example 0.001 to 0.010 mol dm-3 (5 or more values)
- You measure
- Pseudo-first-order rate constant (s-1) from the exponential decay of dye absorbance
- You keep the same
- Initial dye concentration
- Temperature
- Wavelength
- pH (bleach is alkaline; do not add acid)
Method
Mix a fixed amount of food dye (such as brilliant blue) with diluted bleach in the colorimeter cuvette and log absorbance against time. Repeat with different bleach concentrations.
Data analysis
Fit ln(absorbance) against time for each run to get k; plot log k against log [bleach] for the order; propagate uncertainties; compare the shape with a first-order model.
How it works
You change Bleach concentration (mol dm⁻³) and measure Rate constant k (s⁻¹) in Food dye + diluted bleach, keeping Dye concentration, Wavelength, Temperature the same. Expect a graph of Rate constant k / s⁻¹ against [Bleach] / mol dm⁻³: More bleach should fade the dye faster.
Make it yours
Vary temperature for Ea, or change dye.
Extended Essay angle
Interpret the result with a proposed mechanism and test an alternative using different pH.
Safety
Take care with: hazardous chemicals.
Bleach is corrosive in concentration and releases chlorine if mixed with acid: dilute it, never add acid, use eye protection.
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