Experiment 18: Cis-Trans Isomers of But-2-enedioic acid
Cis-trans isomers are a kind of stereoisomers called geometrical isomers. Due to the inability of rotation about the C=C bond, some compounds possess cis and trans isomers. But-2-enedioic acid is an example of having both isomers.
Maleic acid Fumaric acid
Cis and trans isomers have different physical properties such as boiling 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 as a catalyst of the reaction. The properties of two acids are then compared.
Maleic acid, magnesium ribbon, sodium carbonate, concentrated hydrochloric acid, bromine water, pH paper
100cm3 and 250cm3 beakers, watch glass, apparatus for suction filtration (Büchner funnel and filter flask), melting point apparatus, 25 cm3 measuring cylinder
AConversion of maleic acid to fumaric acid.
1. Weigh out about 4g of maleic acid in a clean dry 100cm3 beaker. Add 10cm3 of deionised water and warm slightly to dissolve the acid. 2. Add 10cm3 of concentrated hydrochloric acid, and cover the beaker with a watch glass. Place the beaker inside a 250cm3 beaker which is about one third full of water. Heat this water 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. Filter 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 and dry the crystals by...