Melting Points — Lab Prep

Source: Lara Al Hariri at the University of Massachusetts Amherst, MA, USA

  1. Preparation of the Laboratory

    Here, we show the laboratory preparation for 10 students working in pairs, with some excess. Please adjust quantities as needed.

    • To set up for this lab experiment, wear the appropriate personal protective equipment, including a lab coat, chemical splash goggles, and gloves.
    • 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.
    • 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’.
    • Obtain enough naphthalene for each group to have 1 mg.
    • 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.
    • 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.
    • Place a 2-ft section of glass tubing on a communal bench for students to use during the lab.
    • 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