(10 pts) Consider the experimental description below for the separation of a mix

Question

(10 pts) Consider the experimental description below for the separation of a mixture of benzoic acid and acetanilide by base extraction. The experimental methods and analyses contain a number of mistakes and oversights. Based upon your experience in the laboratory, find 10 of these errors and briefly state the nature of the error as well as a suitable correction. No explanation d correction - no credit. List corrections below; do not make corrections within the paragraph iself A 1:1 mixture of benzoic acid and acetanilide was dissolved in diethyl ether and poured into a graduated cylinder. A 3.0 M basic aqueous solution of Na,CO, was then added to the organic solution. Deprotonation of benzoic acid gives its conjugate base benzamide, which is equally soluble in the aqueous phase and the organic phase. The two phases were then separated The denser organic phase was the top layer. After separating the two phases, the organic phase was extracted with an additional portion of aqueous base. Likewise, the aqueous phase was extracted with an additional portion of organic solvent. Fewer extractions with larger volumes of extracting solvent result in more efficient extraction. The aqueous solution was neutralized with 3.0 M HCI, whereupon benzoic acid precipitated from solution and was collected by vacuum filtration on a Büchi funnel Similarly, acetanilide was isolated by neutralizing the organic layer with 3.0 M HCI. Both solids were purified by recrystallization from boiling ethanol. The identity of each solid was confirmed by infrared spectroscopy. Both spectra exhibited an intense, sharp band at approximately 1200 cm, which corresponds to the carbonyl functional group present in both. The i solid was confirmed by melting point analysis since the melting points of pure substances are generally sharp lting range); impurities or mixtures generally cause melting point elevation and a broadening of the melting range. Mistake/Error Explanation & Correction 2. 10

Explanation / Answer

Extraction

Errors

1. 1:1 mixture is poured in graduated cyllinder

Explanation/correction : Separatory funnel is used for extractios and separations and not cyllinders.

2. Benzamide has same solubility in aqeuous and organic phase

Explanation/correction : benzamide being non-polar would go preferably in organic phase. It has no solubility in aqueous phase.

3. The organic layer is more denser and stays at top.

Explanation/correction : Diethyl ether is less denser and therefore stays at the top.

4. Fewer extractions with large volumes is more efficient

Explanation/correction : Fewer extractions with small volumes is more efficient.

5. Acetanilide was extracted by adding HCl to organic layer

Explanation/correction : Acetanilide is already in neutral form in organic layer and nu such acidification is needed.

6. Ethanol is used as recrystallizing solvent for the two

Explanation/correction : Both have considerable solubility in ethanol at room temperature and not best solvent. Instead water is choosen solvent for recrystallization.

7. Peak at 1200 cm-1 is for carbonyl

Explanation/correction : Carbonyl peaks come at around 1650-1800 cm-1 region only.

8. impurities cause melting point elevation

Explanation/correction : impurities break the intermolecular forces and thus lower the melting point when present in a compound.

9. deprotonation of benzoic acid gives benzamide its conjugate bas

Explanation/correction : benzoic acid forms benzoate upoj deprotonation

10. conjugate base of benzoic acid has equal solubility in aqueous and organic layer

Explanation/correction : conjugate base is ionic in nature and hence has more solubility in water and insoluble in organic layer.

Related Questions

Navigate

• Browse (All)
• Browse #
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.