Which of the following is a characteristic difference between colloids and true solutions?

The correct answer is True solutions have a single-phase system, whereas colloids have a two-phase system.

Key Points

• True solutions are homogeneous mixtures in which the solute is completely dissolved in the solvent, forming a single-phase system.
• Colloids, on the other hand, are heterogeneous mixtures with two distinct phases: the dispersed phase (solute-like) and the dispersion medium (solvent-like).
• The particles in true solutions are molecular or ionic in size (<1 nm), whereas colloidal particles range from 1 nm to 1000 nm.
• True solutions do not scatter light and hence do not exhibit the Tyndall effect, while colloids do scatter light due to their larger particle size.
• True solutions are stable without any separation of components, whereas colloids may show sedimentation over time under certain conditions.

Additional Information

• Brownian motion: The random, zigzag motion of particles in a fluid medium, observed prominently in colloids due to their particle size. True solutions do not exhibit Brownian motion as their particles are too small.
• Tyndall effect: The scattering of light by particles in a colloid, making the light beam visible. True solutions do not exhibit this effect as their particles are too small to scatter light.
• Homogeneous vs. heterogeneous mixtures: True solutions are homogeneous (uniform throughout), while colloids are heterogeneous (two-phase system but appear uniform to the naked eye).
• Particle visibility: Solute particles in true solutions are invisible under a microscope, while colloidal particles can be seen under an ultramicroscope.
• Examples: True solutions include saltwater and sugar water. Colloids include milk (emulsion), fog (aerosol), and gelatin (gel).