Lab: Chemie
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Source: Lara Al Hariri and Ahmed Basabrain at the University of Massachusetts Amherst, MA, USA
In this lab, you'll learn several important techniques that you'll use throughout this class. This includes measuring the mass or volume of reactants and products, methods of heating and cooling reaction mixtures, proper selection and handling of glassware, and separating solids and liquids by vacuum filtration. First, you'll synthesize benzoic acid by protonating sodium benzoate with hydrochloric acid, or HCl, using water as the solvent. Sodium benzoate is very soluble in water, but benzoic acid is not, so you can filter the solid product out of the solution.
You'll use vacuum filtration, which is used for powdery solids, to filter out the benzoic acid. Benzoic acid is less soluble in water at lower temperatures, so you'll collect more product if you cool the reaction solution before you filter it. When you do this lab, remember that HCl is toxic and a strong acid. It's always best to work with strong acids and organic solvents in a fume hood. If you spill any HCl, follow your lab's procedures for neutralizing and cleaning up strong acids.
Mass of sodium benzoate (g) |
Moles of sodium benzoate |
Volume of HCl (mL) |
Moles of HCl |
Moles of benzoic acid |
Mass of benzoic acid (g) |
Theoretical yield | |||||
- | - | - | - | Percent yield |
While your benzoic acid dries, you'll practice refluxing tetrahydrofuran, or THF, which has a boiling point of 66 °C. THF is volatile, flammable, and an irritant, so avoid letting it touch your skin and always work with it in a fume hood. Refluxing is a technique that constantly condenses the vapor and returns it to the flask. This allows reactions to be performed at high temperatures, such as at the solvent's boiling point, without losing the solvent to evaporation.
Refluxing is achieved with a special piece of glassware called a condenser, which is attached directly to your flask. The condenser is cooled with water flowing through the outer chamber. As vapor rises through the condenser, it loses heat to the cool walls, condenses, and drips back into the flask.
Refluxing is usually performed in a round-bottom flask. These flasks must be heated in a heating bath or with specialized equipment, but they provide more even heating than an Erlenmeyer flask or beaker as a result. Water baths are typically used for experiments performed below 80 – 100 °C.