Representations of Solutions
Introduced| English |
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| electrolyte/ɪˈlektrəlaɪt/ |
Drawing what's dissolved
- Zoom into salt water and you will not find salt crystals.
- You find separate sodium and chloride ions adrift.
- A good particle picture shows exactly what floats where.
- Reading these diagrams tells you what a solution really contains.
The particle-level picture
- A particulate diagram shows the actual particles in a solution.
- Water molecules surround each dissolved particle.
- The picture must match the real ratio of particles.
A particle diagram must show the particles in their correct ratio.
The drawing has to match the real ratio of dissolved species.
Splitting into ions
- An electrolyte 电解质 breaks into ions when it dissolves.
- $\text{NaCl} \to \text{Na}^+ + \text{Cl}^-$ gives two separate ions per unit.
- These free ions let the solution conduct electricity.
When $\text{NaCl}$ dissolves, a particle diagram should show...
Ionic compounds dissociate into separate ions in solution.
A solution of an electrolyte conducts electricity because it contains free ions.
Mobile ions carry charge through the solution.
Ions or whole molecules
- Ionic compounds dissociate into ions, so they are electrolytes.
- Molecular solutes like sugar dissolve as whole molecules.
- So sugar water does not conduct, but salt water does.
A dissolved salt, particle by particle
Tap each part of a sodium chloride solution to see how water keeps the ions apart.
When sugar dissolves in water, it exists as...
Sugar is molecular, so it dissolves without splitting into ions.
A solute that dissolves as whole molecules and does not conduct is a ____.
No free ions means it is a nonelectrolyte.
Draw dissolved $\text{CaCl}_2$ at the particle level.
- Each unit gives one $\text{Ca}^{2+}$ and two $\text{Cl}^-$.
- So the picture shows twice as many chloride ions as calcium ions.
When $\text{CaCl}_2$ dissolves, how many chloride ions form per formula unit?
$\text{CaCl}_2 \to \text{Ca}^{2+} + 2\,\text{Cl}^-$, so two chloride ions.
When an ionic compound dissolves, draw separate ions, not intact "NaCl" units -- they dissociate. Keep the correct ratio ($\text{CaCl}_2$ gives 1 $\text{Ca}^{2+}$ to 2 $\text{Cl}^-$). And molecular solutes like sugar stay whole, so do not split them into ions.
A particulate diagram shows a solution's real particles in their true ratio. An electrolyte (an ionic compound) dissociates into separate ions and conducts electricity, while a molecular solute like sugar dissolves whole and does not. Draw ions for salts, whole molecules for sugars.