IB Chemistry IA idea · Materials and polymers
IB Chemistry IA idea: where is the lowest melting point of two fatty acids?
Two solids mixed melt at a lower temperature than either alone; map the full curve with a cooling curve.
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 composition of lauric and stearic acid mixtures (mole fraction of lauric acid 0, 0.2, 0.4, 0.6, 0.8 and 1.0) affect the freezing temperature (°C) read from a cooling curve?
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
- Composition of a mixture of lauric and stearic acid (mole fraction of lauric acid), 0 to 1 in 6 or more steps
- You measure
- Freezing temperature from the cooling curve (degrees C)
- You keep the same
- Total mass of the mixture
- Cooling method and stirring
- Temperature logger and start temperature
- Purity of acids
Method
Melt weighed mixtures in a boiling tube in a hot water bath, then cool slowly while a temperature probe logs the temperature; read the freezing point from the plateau or slope change.
Data analysis
Plot freezing point against composition (phase diagram); find the eutectic; compare with an ideal-solution model; propagate uncertainty.
How it works
You change Lauric acid fraction (mole fraction) and measure Freezing temperature (°C) in Lauric–stearic acid mixtures, keeping Total mass, Cooling rate, Stirring the same. Expect a graph of Freezing temperature / °C against Mole fraction of lauric acid: The lowest point marks the eutectic.
Make it yours
Add a third component or try another pair (for example palmitic and stearic acid).
Extended Essay angle
Test the Schroder-van Laar equation and thermodynamic ideality for the mixtures.
Safety
Take care with: heat and hot liquids.
Hot water bath at about 80 degrees C scalds; fatty acids are low hazard.
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