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investigation of properties of a pair of cis, trans isomers

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Introduction

TAS experiment No 18 (Chung Pui Wu) 1. Date 2. Title Investigation of properties of a pair of cis, trans isomers 3. Objective Determine the percentage yield of fumaric acid. Compare the properties, like solubility in water , acid strength and reaction with acidified potassium permanganate, of the cis and trans isomers (maleic acid and fumaric acid). 4. Introduction Butenedioic acid, C4H4O4, exists as two distinct geometrical isomers: These two isomers of butenedioic acid are commonly known as maleic acid and fumaric acid (not necessarily in that order). Each of them has its own distinctive properties such as melting point, solubility in water, density and stability. In this experiment you will convert some maleic acid to fumaric acid by heating in an aqueous solution containing some hydrochloric acid, which serves as a catalyst. You will then compare the properties of these two isomers and use the results to identify which isomer is maleic acid and which isomer is fumaric acid. 5. Procedure Day 1 Part A - Conversion of maleic acid to fumaric acid 1. Weigh out about 4g of maleic acid in a clean, dry 100cm3 beaker. Record the mass accurately. 2. Add about 15cm3 of distilled water to beaker. Warm the mixture slightly to dissolve the acid completely. 3. Add about 10cm3 of concentrated hydrochloric acid to the beaker, and cover it with a small watch glass. ...read more.

Middle

Reaction with acidified potassium permanganate Maleic acid decolourizes acidified potassium permanganate solution. The volume of maleic acid required = 6cm3 Fumaric acid cannot decolourize acidified potassium permanganate solution. 7. Questions 1. Calculate the percentage yield of fumaric acid in this experiment. 2. Why is it important to use chilled distilled water when filtering the fumaric acid formed? 3. Write the chemical equations for the reactions of cis-butenedioic acid and trans- butenedioic acid with the following: a) magnesium b) sodium carbonate c) acidified potassium permanganate 4. With the reference to the data obtained in the tests of solubility in water and acid strength ,state which isomers of butenedioic acid (cis or tans) maleic acid and fumaric acid correspond to. Explain your reasons. 5. What is the purpose of the test with acidified potassium permanganate? 6. One of the isomers can undergo dehydration to form a cyclic anhydride. Explain which one it is with the help of a chemical equation. (1) The percentage yield of fumaric acid in this experiment is 42.7%. (2) Use chilled distilled water to make the fumaric acid to be more saturated. The solubility of fumaric acid is much insoluble in water as there is no net dipole moment in fumaric acid. When adding chilled distilled water which makes lower temperature environment, more furnaric crystal would be formed by saturation. (3) a) reaction of cis-butenedioic acid with magnesium + 2Mg � H2 + reaction of trans-butenedioic acid with magnesium + 2Mg � H2 + b) ...read more.

Conclusion

It's because the equilibrium shift much towards the fumaric acid side. In fumaric acid, the two bulky carboxyl groups (-COOH) are further apart and experience less steric repulsion. Part B experiments show maleic acid is more soluble and acidic than fumaric acid. The oxidizing power of maleic acid is higher than fumaric acid. There are some sources of error in the experiment. In part A experiment, when placing the beaker containing maleic acid, conc. HCI inside the bigger beaker, our group let large amount of tap water add to the maleic acid. It lowers the conc. of maleic acid and thus obtain less amount of solid of fumaric acid. The percentage yield of fumaric acid I calculated is lower than 50%. So the reaction mixture should be placed carefully and prevent water affect its conc. It's hard to ensure to maleic acid is 100% pure to be converted to fumaric acid. As the maleic acid has impurities, the fumaric acid produced also has impurities. The percentage yield of fumaric acid I calculated is lower than the accurate value. There is loss of maleic acid when it is heated. It's because maleic acid is heated to gas state. The vapour of maleic acid may return to the tap water in the bigger beaker instead of the mixture. It reduces the amount of fumaric acid produced. The percentage yield of fumaric acid I calculated is lower. 9. Conclusion The percentage yield of fumaric acid in this experiment is 42.7%. Maleic acid is more soluble and acidic than fumaric acid. Maleic acid decolourize acidified potassium permanganate while fumaric acid does not. ...read more.

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