A liquid pharmaceutical preparation shows a distinct illuminated path when a beam of light… — JAMB UTME

A liquid pharmaceutical preparation shows a distinct illuminated path when a beam of light passes through it in a dark room (Tyndall effect) and shows no settling of particles upon standing for several weeks. However, when poured through standard filter paper, it leaves no residue. Which of the following correctly classifies this liquid system and explains its observed behavior?

A
It is a true solution because its solute particles are fully dissolved, homogeneous, and smaller than $1\text{ nm}$ .
It is a colloidal system because its dispersed particle diameters ( $1\text{ nm}$ to $100\text{ nm}$ ) are large enough to scatter light but small enough to pass through standard filter paper pores.Answer
C
It is a suspension because its dispersed phase particles are kept suspended solely by thermal convection currents within the solvent.
D
It is a true solution because its particles undergo rapid sedimentation only when exposed to atmospheric air.

Answer

The liquid preparation is a colloidal system because its dispersed particles (diameters between

1\text{ nm}

and

100\text{ nm}

) are sufficiently large to cause the Tyndall effect by scattering light, yet small enough to pass unhindered through the pores of standard filter paper without settling.

The correct response identifies the mixture as a colloidal system. Colloidal particles range in diameter from

1\text{ nm}

100\text{ nm}

. This intermediate particle size makes them small enough to pass through the microscopic pores of standard laboratory filter paper while remaining large enough to scatter incident light beams (Tyndall effect) and stay suspended indefinitely via Brownian motion.

Step-by-Step Solution

Analyze the light scattering observation.

The observation of a visible light path (Tyndall effect) rules out true solutions, which have particle sizes smaller than

1\text{ nm}

and do not scatter light.

Particles must be comparable in size to the wavelength of light (

1\text{ nm}

100\text{ nm}

) to scatter light effectively.

Analyze the filtration and stability observations.

Passage through standard filter paper without leaving a residue and absence of settling rules out suspensions.

Suspension particles exceed

100\text{ nm}

(or

0.1\text{ }\mu\text{m}

), causing them to be trapped by filter paper pores and to settle under gravity over time.

Synthesize particle size characteristics to classify the system.

The mixture exhibits properties unique to a colloidal dispersion.

Colloids uniquely combine stability against gravity, ability to pass through ordinary filter paper, and distinct scattering of light.

Key Concept

Physical distinction between true solutions, colloids, and suspensions based on particle size, filtration capability, and light scattering (Tyndall effect).

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Answer

Step-by-Step Solution

Key Concept

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