Which solutions conduct
Whether a substance is held together by ionic or covalent bonds can be settled by an experiment that takes only a few minutes: see whether its solution conducts electricity.
Activity 03
Testing four solutions
You will need four beakers, two carbon rods, a bulb, two batteries, connecting wires and clips.
- Label four identical beakers A, B, C and D.
- Put common salt solution in A, copper sulfate solution in B, sugar solution in C and distilled water in D.
- Stand the two carbon rods in each beaker in turn, complete the circuit, and note whether the bulb lights.
- Wash the carbon rods well before moving to the next beaker.
Figure to be added
What is observed
| Beaker | Contents | Bulb |
|---|---|---|
| A | Common salt solution | Lights |
| B | Copper sulfate solution | Lights |
| C | Sugar solution | Does not light |
| D | Distilled water | Does not light |
Reading the result
Common salt and copper sulfate are ionic compounds; sugar and water are covalent. So the compounds that conducted are exactly the ionic ones.
A current is a flow of charge, and it needs charged particles free to move. Dissolving an ionic compound releases its ions into the water, where they can travel. A covalent compound dissolves as whole, uncharged molecules, and there is nothing for the current to move.
Solid, molten, dissolved
Experiment has also shown that molten common salt conducts. But an ionic compound in the solid state does not — and the reason is the lattice.
| State of an ionic compound | Can the ions move? | Conducts? |
|---|---|---|
| Solid | No, they are locked in the lattice | No |
| Molten | Yes, the lattice has broken down | Yes |
| Dissolved in water | Yes, the ions are free in solution | Yes |
Having ions is not enough
Solid salt is made entirely of ions and still does not conduct. What a current needs is charged particles that are free to move, and in the lattice they are held fast.