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A membrane cell is where the electrolysis of sodium hydroxide can be carried out. The products of the electrolysis of sodium chloride are chlorine, sodium hydroxide and hydrogen.

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Introduction

A membrane cell is where the electrolysis of sodium hydroxide can be carried out. The products of the electrolysis of sodium chloride are chlorine, sodium hydroxide and hydrogen. 2Na+(aq) + 2Cl- (aq) = 2Na+(aq) + Cl2 (g) + 2e- The Chlorine is collected at the positive electrode called the anode. In the reaction the Na+ ions acts an as a spectator. 2Cl- (aq) = Cl2 (g) + 2e- The half equation of what happens at the anode tells us that the chlorine ions have been oxidised. (1) The hydrogen and the hydroxide ions are gathered at the negative electrode, which is better known as the cathode. 2Na+(aq) + 2H2O(l) + 2e- = H2 (g) + 2OH-(aq) The half equation shows us that the water molecules from the hydrogen and the hydroxide ions have been reduced as they have gained electrons. (1) 2H2O(l) + 2e- = H2 (g) + 2OH-(aq) This is known as a Redox reaction because its composed of two half equations, in which one is of reduction and the other is of oxidation. ...read more.

Middle

(4) The membrane cell However this membrane cell was used until early 1970's because of poor quality materials of the membrane (5) There are 4 points, which a membrane cell should: * Permeable to Na+(aq) ions * Impermeable to Cl- (aq) ion * Resist to chlorine and sodium hydroxide solution that is almost 9 mol dm-3 * Stable at approximately 90?C Most modern methods of extracting chlorine and iodine involves either electrolysis to extract the chlorine or by redox reactions of brine to extract the iodine. This is a modern technique. Iodine can also be extracted from kelp, which is obtained by burning seaweed. Salts such as sodium chloride, potassium chloride, and potassium sulphate are removed from the kelp by washing with water. The residue is then heated and concentrated, the iodine is liberated Chlorine and iodine are both from group 7 in the periodic table, halogens, which means they have similar chemical properties. ...read more.

Conclusion

The solution of iodide ions are mixed with tiny amounts of the original Iodate(V) solution to liberate the iodine. (7) The methods of extraction of iodine between the nineteenth and twentieth century have changed dramatically. These changes are mainly due to improvement in technology and the chance of discovery by accident. The accident has turned out to be a vital part of modern life. As technology becomes more and more advanced the properties of elements and the way that they react will be discovered more intensely. They are many uses of the products or electrolysis of sodium chloride. The pie charts below show the main ones. The annual world production of chlorine is about 39 million tonnes per year. The miscellaneous products are those of water treatment and insecticides. 41 million tonnes of the sodium hydroxide is produced every year. The hydrogen is mainly used to make ammonia. 36 million tonnes of hydrogen is produced every year. At the present day the annul production of iodine is about 13000 tonnes per year. This is fairly a small amount compared to the products of the electrolysis of sodium chloride. ...read more.

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