Experiment O07

Investigation of some of the properties ofa pair of cis-trans isomers

Name:

Seat No.:

Date:

Grade:

Results:

A.Conversion of maleic acid to fumaric acid

Mass of fumaric acid + watch glass / g
Mass of watch glass / g
Mass of fumaric acid / g
Percentage yield / %

B.Comparison of properties of the two isomers

1. Water solubility: acid is more soluble.

2. Melting point of maleic acid:

Melting point of fumaric acid:

  1. Acid strength

Test / Maleic acid / Fumaric acid
pH of solution / PH = 2 / PH = 3
Reaction with Mg / A colourless gas was
given out at a faster rate. / A colourless gas was
given out at a lower rate.
Reaction with Na2CO3 / A colourless gas was
given out at a faster rate. / A colourless gas was
given out at a lower rate.

4. Reaction with bromine water

Maleic acid: The brown bromine water decolourized.

Fumaric acid: The brown bromine water decolourized.

P.4

Experiment O07

Investigation of some of the properties ofa pair of cis-trans isomers

Questions:

1. Assuming that equilibrium concentration was achieved inprocedure A, which isomer would you classify as the morestable with respect to transformation of one into the other?

Trans-isomer, i.e. Furmaric acid.

2.Explain the difference in reaction with magnesium and sodium carbonate between maleic acid and fumaric acid.

Maleic acid reacts with magnesium and sodium carbonate faster than fumaric acid. Since both acids are weak acids, their acidity depends on the first ionization of the carboxyl group. Maleic acid is much stronger than fumaric acid in the first ionization. Since the reaction with magnesium and sodium depends on the acid strength, maleic acid reacts faster.

3. Considering the structures of the two isomers, try to accountfor the observed differences in solubility and melting point.

Maleic acid has higher solubility than fumaric acid.

The molecules of maleic acid have a stronger net dipole moment than fumaric acid. The molecules of maleic acid are polar and are easily hydrated by the polar water molecules.

Moreover, the molecules of fumaric acid are more tightly packed compared with those of maleic acid.

The melting point of fumaric acid is much higher than maleic acid.

The molecules of fumaric aicd.

4. One of the isomers can lose a molecule of water from eachmolecule of acid when its two carboxyl groups react to forman anhydride. Which geometrical isomer, cis- or trans-,do you predict it is?

Cis-isomer.

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