Electrostatic Deflection of Polar vs Nonpolar Liquids

Charged rods can bend a falling stream of polar liquid, such as water, but have no effect on a stream of nonpolar liquid, such as cyclohexane. This demonstrates molecular polarity and explains why polar solvents dissolve ionic compounds.

1. Rub a rubber rod with fur to give it a negative static charge.
2. Open the stopcock of a burette filled with water to produce a steady stream.
3. Bring the charged rubber rod near the water stream; it bends toward the rod.
4. Repeat with the charged glass rod; the water stream again bends toward the rod.
5. Replace the water with cyclohexane in a second burette. Produce a stream and repeat the test with both charged rods. Observe that the cyclohexane stream is not deflected.

A demonstration of polar vs non-polar molecules - Blake Wheaton:

📄 Polarity - Bending of a Liquid Stream - Rutgers-New Brunswick School of Arts and Sciences: https://chem.rutgers.edu/cldf-demos/1557-polarity-bending-of-a-liquid-stream

• Try other polar liquids (e.g., ethanol, vinegar) to compare their deflection strength.
• Use different nonpolar liquids (e.g., hexane, oil) to confirm lack of deflection.
• Compare the degree of bending for different distances between the rod and the liquid stream.

• Handle glass rods and burettes with care to prevent breakage.
• Cyclohexane is flammable - keep away from flames or sparks and work in a well-ventilated area.
• Dispose of organic solvents according to local laboratory safety protocols.

• Why does water bend toward both positively and negatively charged rods? (Because water is polar; its dipoles align so that the opposite end is attracted to the rod regardless of the rod’s charge.)
• Why does cyclohexane not bend? (Because cyclohexane is nonpolar and has no permanent dipole to align with an electric field.)
• How does this experiment help explain why ionic compounds dissolve in water but not in cyclohexane? (Ions are stabilized by attraction to water’s dipoles, but no such stabilization occurs in nonpolar solvents.)
• Would you expect salt (NaCl) to dissolve better in water or in cyclohexane? Why? (In water, because of ion-dipole attraction.)