Jove Lab Chem
Melting Points — Lab Prep
Source: Lara Al Hariri at the University of Massachusetts Amherst, MA, USA
- Preparation of the Laboratory
Here, we show the laboratory preparation for 10 students working in pairs, with some excess. Please adjust quantities as needed.
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To set up for this lab experiment, wear the appropriate personal protective equipment, including a lab coat, chemical splash goggles, and gloves.
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Prepare a mixture of urea and benzoic acid in a mass ratio of 4 to 1. Tare a weighing boat and measure 0.48 g of urea. Use a powder funnel to transfer the urea to a glass vial.
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Weigh 0.12 g of benzoic acid and add it to the vial. Mix the solids thoroughly by stirring with a spatula and shaking the closed vial. Label the vial as ‘urea with unknown’.
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Obtain enough naphthalene for each group to have 1 mg.
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Label a 50-mL beaker for solid waste and set it along with the naphthalene, the bottle of pure urea, and the mixture of urea and benzoic acid near the balance.
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For each group, pour about 150 mL of mineral oil into a 250-mL beaker. Distribute the baths to the student’s workstations before the lab.
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Place a 2-ft section of glass tubing on a communal bench for students to use during the lab.
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Set out the following glassware and equipment at each student lab station (we suggest that students work in pairs):
1 Stir bar 1 Stirring hotplate 1 Lab stand 1 Thermometer clamp 1 Digital thermometer (pre-calibrated, 60 – 150°C) 4 Melting point capillary tubes 3 Metal spatulas 3 Watch glasses 1 Rubber band
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