Podstawowe techniki chemii organicznej
View the full transcript and gain access to JoVE Lab Manual videos
Q1: Why is cooling the reaction solution important before filtering benzoic acid?
Benzoic acid is less soluble in water at lower temperatures, so cooling the reaction solution to 10 °C before vacuum filtration increases product recovery. The decreased solubility causes more benzoic acid to precipitate from solution, allowing you to collect a higher yield of solid product from the filtered mixture.
Q2: What is the purpose of refluxing in organic chemistry experiments?
Refluxing allows reactions to proceed at high temperatures, such as at the solvent's boiling point, without losing solvent to evaporation. A condenser constantly cools and condenses rising vapor, returning it to the flask. This technique enables sustained heating for reactions requiring elevated temperatures while conserving the reaction solvent.
Q3: How does vacuum filtration differ from standard filtration for collecting benzoic acid?
Vacuum filtration uses reduced pressure to rapidly pull liquid through filter paper, making it ideal for collecting powdery solids like benzoic acid. The pressure difference accelerates the filtration process compared to gravity filtration alone, allowing faster separation of solid product from the liquid reaction mixture.
Q4: What happens when you add hydrochloric acid to sodium benzoate solution?
Adding HCl to sodium benzoate solution protonates the benzoate ion, forming benzoic acid, which precipitates as a solid because it is not soluble in water. The acid-base reaction converts the water-soluble sodium salt into an insoluble organic acid that can be separated by filtration.
Q5: Why is washing the benzoic acid with cold deionized water an important filtration step?
Washing the benzoic acid on the filter removes impurities, side products, and unreacted compounds that may have been trapped with the solid. Using cold water minimizes benzoic acid dissolution while effectively rinsing away unwanted substances, improving product purity and accuracy of yield calculations.
Q6: How do you calculate percent yield for the benzoic acid synthesis?
Convert the mass of recovered benzoic acid to moles, divide by the moles of sodium benzoate used, and multiply by 100. Typical yields range from 80% to 98% because some benzoic acid remains dissolved in solution. Yields above 100% suggest the product was still wet when weighed.
Q7: What safety precautions should you follow when working with hydrochloric acid and tetrahydrofuran?
Always work with HCl and THF in a fume hood because HCl is toxic and a strong acid, while THF is volatile, flammable, and an irritant. Wear a lab coat, safety glasses, and nitrile gloves, changing gloves if they contact acid or organic solvent. Follow your lab's procedures for neutralizing and cleaning up spills.