Question

For a science fair project about food and chemistry, Bill looks around his kitchen for examples of covalent compounds. What evidence can Bill use in his project to show that water (H2O) acts like other covalent compounds?

Answer 1

Useful, simple evidence Bill can collect in his kitchen (with basic, safe equipment) to show that H2O behaves like a covalent (molecular) compound:

1. Electrical conductivity test
- What to do: set up a low‑voltage circuit (battery + small LED or bulb + two metal electrodes). Test distilled water, a salt (table salt) solution, and a sugar solution.
- What it shows: pure (distilled) water conducts very poorly (LED stays off), like other covalent, non‑electrolyte substances. Salt (an ionic compound) dissolves into ions and conducts (LED lights). This contrasts covalent vs ionic behavior.

2. Evaporation/condensation (phase change) demonstration
- What to do: heat a small pan of water until it boils and collect/condense the vapor on a cool plate or lid.
- What it shows: water forms a molecular gas (vapor) and easily returns to liquid by condensation — behavior typical of molecular (covalent) compounds. Compare to an ionic solid like salt, which does not vaporize at these temperatures (it stays as solid residue when water evaporates).

3. Solubility and miscibility with oil
- What to do: mix water and vegetable oil in a clear glass and shake; let it settle.
- What it shows: water (a polar covalent molecule) is immiscible with nonpolar covalent oils. This shows that covalent compounds can be polar or nonpolar and follow “like dissolves like” behavior.

4. Surface tension / hydrogen bonding evidence
- What to do: float a paperclip carefully on the surface of clean water or sprinkle ground pepper and add a drop of dish soap to see surface tension break.
- What it shows: strong intermolecular attraction (hydrogen bonding) between water molecules — an intermolecular feature of many covalent molecules that influences their behavior (high surface tension, capillarity).

5. Comparison of melting/boiling points
- What to do: note that ice melts at 0 °C and water boils at 100 °C, whereas table salt has a very high melting point and does not melt on your stove.
- What it shows: water behaves like a molecular liquid with relatively low melting/boiling points (compared with ionic solids), consistent with covalent molecular compounds (though hydrogen bonding raises water’s boiling point higher than many molecules of similar size).

Safety notes: use distilled water for conductivity tests (tap water contains ions), use low‑voltage circuits and adult supervision for heating.

Using a couple of these simple experiments and comparisons, Bill can demonstrate that water shares key behaviors of covalent (molecular) compounds: poor electrical conductivity when pure, molecular phase changes, polarity/immiscibility patterns, and characteristic intermolecular effects (surface tension).