Maleic acid and fumaric acid are geometrical isomers of butenedioic acid. Each of these isomers has its own distinctive properties such as melting point, solubility, density and stability.
In this experiment some maleic acid is converted to fumaric acid by heating an aqueous solution of maleic acid in the presence of hydrochloric acid. The hydrochloric acid serves merely as a catalyst of the reaction. The properties of these two isomers are then compared.
Maleic acid, magnesium ribbon, Na2CO3, concentrated HCl, bromine water, pH paper
100 cm3 and 250 cm3 beakers, watch glass, apparatus for suction filtration, 25 cm3 measuring cylinder, melting point apparatus
[Hazard Warning: Maleic acid is irritant, concentrated hydrochloric acid is corrosive, and bromine water is harmful.] A. Conversion of maleic acid to fumaric acid
1. Weigh out about 4 g of maleic acid in a clean dry 100 cm3 beaker. Add 10 cm3 of deionized water and warm slightly to dissolve the acid. 2. Add 10 cm3 of concentrated hydrochloric acid, and cover the beaker with a watch glass. Place the beaker inside a 250 cm3 beaker which is about one third full of water. Heat this water bath to boiling for about 5 minutes or until a solid material forms in the small beaker. 3. Cool the solution to room temperature by placing the small beaker with its contents in a cold water bath or in an ice bath. 4. Fitter the reaction mixture by suction using the following set-up:
5. Stop suction, either by lifting the funnel or by disconnecting the tubing, and soak the residue in about 1 cm3 of cold water. (if you turn off the tap, you may get a "suck(back' of water.) 6. Resume suction...