Three unlabelled liquid mixtures, P, Q, and R, are tested in a laboratory. Mixture P passe… — JAMB UTME

Three unlabelled liquid mixtures, $P$ , $Q$ , and $R$ , are tested in a laboratory. Mixture $P$ passes completely through both filter paper and semi-permeable membranes without scattering light. Mixture $Q$ passes through filter paper but is retained by semi-permeable membranes and scatters a narrow beam of light. Mixture $R$ leaves a solid residue on filter paper upon gravity filtration. Which mixture will undergo precipitation upon the addition of an electrolyte, and what physical property accounts for this behavior?

A
Mixture $P$ , because its dissolved solute particles adsorb electrolyte ions to form insoluble precipitates.
Mixture $Q$ , because its dispersed particles carry surface charges and have diameters between $1\text{ nm}$ and $100\text{ nm}$ .Answer
C
Mixture $R$ , because Brownian motion maintains its suspension until electrolyte ions increase its density.
D
Mixture $Q$ , because its solute molecules are smaller than $1\text{ nm}$ and easily aggregate into coarse solids.

Answer

Mixture

Q

, because its dispersed particles carry surface charges and have diameters between

1\text{ nm}

and

100\text{ nm}

The experimental observations identify Mixture

Q

as a colloid because it passes through ordinary filter paper, is retained by a semi-permeable membrane, and displays light scattering (Tyndall effect). Colloidal particles range in size between

1\text{ nm}

and

100\text{ nm}

and carry surface electrical charges. Addition of an electrolyte neutralizes these charges, leading to coagulation.

Step-by-Step Solution

Analyze the filtration and optical properties of each mixture to classify them.

Mixture

P

is a true solution (particle size

< 1\text{ nm}

). Mixture

Q

is a colloidal system (particle size

1\text{--}100\text{ nm}

, exhibits Tyndall scattering, retained by semi-permeable membrane). Mixture

R

is a suspension (particle size

> 100\text{ nm}

, retained by filter paper).

Differentiation among true solutions, colloids, and suspensions is based on particle size and membrane permeability.

Determine which system undergoes coagulation upon adding an electrolyte.

Colloidal particles (Mixture

Q

) carry electric charges that stabilize them. Adding an electrolyte supplies ions of opposite charge, neutralizing the colloidal particles and causing them to coagulate/precipitate.

True solutions do not coagulate on electrolyte addition, and suspensions settle naturally by gravity.

Key Concept

Classification and properties of true solutions, colloidal systems, and suspensions

Question

Answer

Step-by-Step Solution

Key Concept

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