3.6 Representations of Solutions

Particulate Views of Solutions

Particulate diagrams represent solute and solvent particles at the atomic/molecular scale. Solvent molecules (often water) are drawn surrounding solute particles — ions or molecules — showing dissociation for ionic compounds or simple dispersion for molecular compounds. The number and arrangement of particles in a diagram must reflect relative concentration and correct stoichiometric ratios.

Comparing Concentrations Visually

In diagrams comparing two solutions, a more concentrated solution shows more solute particles per fixed volume/number of solvent molecules; a dilute solution shows fewer. When comparing solutions of different solutes, particle count must match the mole ratio given by the formula (e.g., a diagram of CaCl₂ should show twice as many Cl⁻ as Ca²⁺).

Strong vs. Weak Electrolytes

Strong electrolytes (strong acids, bases, soluble ionic salts) dissociate completely, so diagrams show only separated ions, no intact molecules. Weak electrolytes show a mix of intact molecules and a small number of dissociated ions, reflecting partial ionization. Nonelectrolytes are drawn as whole, unionized molecules dispersed among solvent particles.

Key terms

Particulate diagram (solutions)

A drawing showing individual solute and solvent particles, their ratios, and dissociation state to represent a solution at the molecular level.

Strong electrolyte (in diagrams)

Shown as fully separated ions with no intact molecules remaining, since dissociation is complete.

Weak electrolyte (in diagrams)

Shown as mostly intact molecules with a small number of dissociated ions, reflecting partial ionization.

Nonelectrolyte (in diagrams)

Shown as whole, unionized molecules dispersed among solvent particles; does not form ions.

Representing concentration in diagrams

More solute particles per fixed number of solvent particles = more concentrated; fewer = more dilute.

Try an AP-style question

In a particle diagram of NaCl(aq), how should water molecules orient around Na⁺?

1. Randomly, with no orientation
2. Hydrogen atoms pointing toward Na⁺
3. Oxygen atoms pointing toward Na⁺
4. Water molecules shouldn't be near ions