IB Chemistry IA idea · Water and the environment
IB Chemistry IA idea: how conductivity changes as water gets saltier
Sea water, estuaries, soup: a conductivity probe turns salt into a number, but not a straight line.
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 sodium chloride solution (0.001, 0.005, 0.01, 0.05, 0.1 and 0.50 mol dm⁻³) affect conductivity (mS cm⁻¹) at 25 °C, and how well does molar conductivity follow Kohlrausch's law?
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 sodium chloride solution, 0.001 to 0.50 mol dm-3 (6 or more values, log spacing)
- You measure
- Conductivity (mS cm-1) and molar conductivity (S cm2 mol-1)
- You keep the same
- Temperature (water bath)
- Probe calibration and position
- Cell constant
- Purity of water used
Method
Prepare serial dilutions of sodium chloride in deionised water at 25 degrees C and record conductivity with a calibrated probe.
Data analysis
Plot conductivity against concentration, then molar conductivity against square root of concentration; compare with Kohlrausch's law and the limiting molar conductivity in a data book; propagate uncertainties.
How it works
You change NaCl concentration (mol dm⁻³) and measure Conductivity (mS cm⁻¹) in NaCl(aq) dilution series, keeping Temperature, Probe calibration, Deionised water the same. Expect a graph of Conductivity / mS cm⁻¹ against NaCl concentration / mol dm⁻³: Rises with concentration, slightly less steeply at high values.
Make it yours
Compare with potassium chloride or magnesium sulfate and relate to ion charge and size.
Extended Essay angle
Test the Debye-Huckel-Onsager equation quantitatively.
Safety
Low hazard solutions.
More Chemistry IA ideas in Water and the environment
- Does lime water get less soluble when warm?Free with an account
Sugar dissolves better in hot tea; calcium hydroxide does the opposite, and the reason takes you into energetics.
- Does boiling remove hardness from water, and how fast?In the Photon IA Guide
Kettle scale is hardness leaving the water; count how much leaves, and when.
- How much oxygen can water hold as it warms up?Free with an account
Fish gasp in warm ponds; measure how much dissolved oxygen leaves as the temperature rises.
- What changes along a stream or drain: a conductivity and pH transectIn the Photon IA Guide
Take a handheld probe on a walk along a canal or stream and map what the water is carrying.
- How much dye can a spoon of charcoal take out of water?In the Photon IA Guide
Activated charcoal clears colour from water; measure how much it can take and where it fills up.
- Is a descaler stronger than vinegar? Acid strength and limescaleIn the Photon IA Guide
Descaling kettles is a rate problem: how quickly do different acids dissolve calcium carbonate?
- Which isotherm describes dye on charcoal: adsorption models comparedIn the Photon IA Guide
Adsorption is where surface chemistry gets quantitative; test two models against your own data.
Other free Chemistry IA ideas
- Does storage temperature destroy the vitamin C in fortified juice?
- How good are average bond enthalpies? A test on fuels from data
- What makes a hand sanitiser feel cold? Ethanol content and cooling
- Mixing two fatty acids: where is the lowest melting point?
- How fast does bleach fade a food dye, and what sets the rate?
- How much iodine is locked up as triiodide, and what is K?
- Does adding an inert salt improve copper plating?
- How much iron can acid get out of fortified cereal?
- Can a computer tell you which molecules are polar, and by how much?
- Can you cut a titration's waste tenfold without losing accuracy?