Three liquid mixtures, X, Y, and Z, were subjected to laboratory tests to determine their … — JAMB UTME

Three liquid mixtures, $X$ , $Y$ , and $Z$ , were subjected to laboratory tests to determine their physical properties:

- Mixture $X$ scatters a focused beam of light (Tyndall effect), leaves no residue on ordinary filter paper, but fails to pass through a semi-permeable membrane.
- Mixture $Y$ does not scatter light, leaves no residue on ordinary filter paper, and passes freely through a semi-permeable membrane.
- Mixture $Z$ leaves a visible residue on ordinary filter paper and separates into two distinct layers after standing undisturbed.

Which of the following correctly identifies mixtures $X$ , $Y$ , and $Z$ respectively?

Starch mucilage, aqueous sodium chloride, and muddy waterAnswer
B
Aqueous sodium chloride, starch mucilage, and fog
C
Milk of magnesia, starch mucilage, and aqueous glucose
D
Starch mucilage, muddy water, and aqueous sodium chloride

Answer

Mixture X is starch mucilage (colloid), mixture Y is aqueous sodium chloride (true solution), and mixture Z is muddy water (suspension).

Mixture X exhibits the Tyndall effect and is retained only by semi-permeable membranes, which defines a colloidal system such as starch mucilage. Mixture Y shows no light scattering and passes through semi-permeable membranes, characteristic of a true solution like aqueous sodium chloride. Mixture Z forms a residue on filter paper and settles over time, which defines a suspension such as muddy water.

Step-by-Step Solution

Analyze the experimental observations for Mixture X

Light scattering (Tyndall effect) combined with passing through ordinary filter paper but being retained by a semi-permeable membrane uniquely identifies a colloidal system (particle diameter

1\text{ nm}

100\text{ nm}

). Starch mucilage is a lyophilic colloidal sol.

Colloidal particles are small enough to pass through the macroscopic pores of filter paper but too large to pass through ultra-fine pores of semi-permeable membranes.

Analyze the experimental observations for Mixture Y

Absence of Tyndall effect and the ability to pass through both filter paper and semi-permeable membranes indicates a true solution (particle diameter

< 1\text{ nm}

). Aqueous sodium chloride is a homogeneous true solution.

Solute particles in true solutions exist as individual ions or small molecules that do not scatter light and readily pass through semi-permeable membranes.

Analyze the experimental observations for Mixture Z

Retention on ordinary filter paper and settling upon standing identifies a suspension (particle diameter

> 100\text{ nm}

). Muddy water is a classic suspension.

Suspension particles are large and heavy enough to be trapped by standard filter paper and to precipitate out under the influence of gravity.

Key Concept

Classification of mixtures into true solutions, colloidal systems, and suspensions based on particle size, light scattering (Tyndall effect), filtration, membrane permeability, and stability.

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