Four synthesized batches (P, Q, R, and S) of an organic solvent were evaluated for chemica… — JAMB UTME

Four synthesized batches (P, Q, R, and S) of an organic solvent were evaluated for chemical purity against a reference standard. The pure standard possesses a sharp boiling point of $142.0^\circ\text{C}$ , a fixed density of $1.04\text{ g cm}^{-3}$ , and yields a single spot on a thin-layer chromatogram with an $R_f$ value of $0.45$ . The physical data recorded for the four synthesized batches are summarized in the table below:

Batch	Boiling Range ( $^\circ\text{C}$ )	Density ( $\text{g cm}^{-3}$ )	Chromatogram Spots ( $R_f$ )
P	141.8 – 142.2	1.04	0.45
Q	138.0 – 144.5	1.01	0.45, 0.62
R	142.0 – 142.1	1.08	0.45
S	145.0 – 145.2	1.04	0.30

Based on the criteria of chemical purity, which batch represents the pure solvent, and what is the correct explanation regarding Batch R?

Batch P is the pure solvent because it conforms to all physical criteria (narrow boiling range around $142.0^\circ\text{C}$ , matching density of $1.04\text{ g cm}^{-3}$ , and a single $R_f$ spot at $0.45$ ), whereas Batch R is impure because its density deviates from the pure reference value.Cevap
B
Batch R is the pure solvent because it exhibits the sharpest boiling range ( $142.0 – 142.1^\circ\text{C}$ ), indicating that density variation is irrelevant when the boiling range is extremely narrow.
C
Batch Q is the pure solvent because the presence of two chromatogram spots ( $0.45$ and $0.62$ ) confirms that the sample undergoes beneficial fractional separation during testing.
D
Batch S is the pure solvent because an elevated boiling range ( $145.0 – 145.2^\circ\text{C}$ ) demonstrates greater chemical stability and structural purity than the reference standard.

Cevap

Batch P is the pure solvent because it satisfies all physical criteria of purity (narrow boiling range at

142.0^\circ\text{C}

, density of

1.04\text{ g cm}^{-3}

, and a single chromatographic spot at

R_f = 0.45

), whereas Batch R is impure due to its higher density of

1.08\text{ g cm}^{-3}

The correct option states that Batch P is the pure solvent because it meets all specified physical criteria of purity: a narrow boiling range centered at the reference temperature (

141.8–142.2^\circ\text{C}

142.0^\circ\text{C}

), a matching density (

1.04\text{ g cm}^{-3}

), and a single chromatographic spot at

R_f = 0.45

. Batch R, despite its narrow boiling range, has an elevated density of

1.08\text{ g cm}^{-3}

, proving the presence of a dissolved impurity.

Adım Adım Çözüm

Analyze the chromatographic data for all four batches.

Batch P, R, and S each show a single spot, whereas Batch Q shows two spots (

R_f = 0.45

and

0.62

A pure substance must yield a single spot on a chromatogram under a given solvent system. Two spots prove Batch Q is a mixture.

Evaluate the boiling point ranges against the reference boiling point (

142.0^\circ\text{C}

Batch P (

141.8 - 142.2^\circ\text{C}

) and Batch R (

142.0 - 142.1^\circ\text{C}

) boil sharply around

142.0^\circ\text{C}

. Batch Q boils over a wide range (

138.0 - 144.5^\circ\text{C}

), and Batch S boils at an elevated temperature (

145.0 - 145.2^\circ\text{C}

Impure liquids boil over a wide temperature range or show boiling point elevation due to non-volatile impurities.

Compare the measured densities against the reference density (

1.04\text{ g cm}^{-3}

Batch P and Batch S have densities of

1.04\text{ g cm}^{-3}

, whereas Batch R has a density of

1.08\text{ g cm}^{-3}

Chemical purity requires that all physical constants, including density and refractive index, match the reference values exactly.

Synthesize the findings across all criteria to identify the single pure batch.

Only Batch P meets all three physical criteria simultaneously: narrow boiling range around

142.0^\circ\text{C}

, matching density of

1.04\text{ g cm}^{-3}

, and a single

R_f

spot at

0.45

Batch R fails on density, Batch Q fails on chromatogram spot count and boiling range, and Batch S fails on boiling point and

R_f

value.

Anahtar Kavram

Criteria of Chemical Purity for Liquids

Tahmini Süre:3m 0s

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