Enthalpy of Reaction

Source: Smaa Koraym at Johns Hopkins University, MD, USA

1. Preparation of 2.0 M Hydrochloric AcidExpand

   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. Hydrochloric acid is extremely corrosive. So, all hydrochloric acid solutions must be used carefully in a fume hood.
   • Prepare 2 L of 2 M HCl, first, carefully measure 330 mL of 12.1 M HCl with a 500-mL graduated cylinder. Close the bottle of concentrated HCl when finished.
   • Place a funnel in the mouth of a 2-L volumetric flask, and carefully pour the HCl into the flask. Then, slowly add 1 L of deionized water to the flask.
   • Place the funnel on a clean surface and seal the top with plastic paraffin film. Carefully invert the flask several times until the mixture appears homogeneous.
   • Then, remove the film and fill the volumetric flask to the line with deionized water.
   • Stir the solution with a large magnetic stir bar until thoroughly mixed, which usually takes 20 – 30 s. Then, turn off the stir plate, remove the flask, and retrieve the stir bar.
   • Label a 2-L glass bottle with ‘2 M HCl’. Then, place the funnel in the mouth of the labeled bottle and carefully transfer the 2 M HCl solution from the flask to the bottle. Cap the bottle and store it in the hood reserved for the instructor.
   • Lastly, put away the concentrated HCl and clean your glassware according to your institution's procedures.
2. Preparation of the LaboratoryExpand
   • Ensure there is a properly labeled waste container for aqueous magnesium waste, per your institution's procedures.
   • Next, set up each fume hood. Refer to the table of materials for a list of equipment. Place a 125-mL plastic wash bottle filled with deionized water in each hood.
   • Cut an approximately 2-inch x 2-inch piece of emery paper for each group.
   • Set out the following lab equipment and glassware at each lab station (we suggest that students work in pairs):

     1    150-mL beaker

     1    600-mL beaker

     1    50-mL graduated cylinder

     1    70-mm watch glass

     1    Digital thermometer

     1    Stir bar

     1    Forceps

     1    Piece of emery paper

     1    Pair of scissors

     2    Polystyrene cups

     1    Cardboard lid with a hole in the center

   • Set out boxes of baking soda, packages of pH paper for neutralizing acid waste, and plastic pipettes for adjusting volume measurements. Ensure that there are paper towels by each lab sink.
   • Prepare the temperature data recording devices. Confirm that the devices are working and charged before distributing them to the fume hoods.
   • Bring a container of magnesium oxide, a package of magnesium ribbon, and a pair of scissors for cutting magnesium to the balance area.
   • Confirm that there is a waste container and a sufficient supply of weighing boats, clean spatulas, and laboratory wipes at the balances.
   • Label a clean, airtight box or bag with ‘magnesium metal pieces’. Cut a piece of magnesium ribbon with a mass of 0.45 – 0.55 g for each student group and place the pieces in the container. Note: Calculate the needed length in advance to help you reliably cut pieces of the appropriate mass.
   • Save any pieces that are too small in a separate container. Afterward, dispose of the weighing boat and put away the scissors.
   • Store the sealed containers of magnesium ribbons in the instructor's hood. Place a stack of weighing boats next to the magnesium ribbons.