Davy_-_new_elements_from_electrolysis

Davy_-_New_Elements_from_Electrolysis

Overview

Electrolysis is the method of separating chemically bonded compounds by running an electric current through the compound. Electrolysis is consequently usually used with an ionic substance that is molten or dissolved in a solvent. Humphry Davy, a pioneer of electrolysis, discovered several alkali and alkali earth elements through this method. This article mainly discusses Humphry's 1808 experiments with potash (KOH) and soda (NaOH), which resulted in the discovery of potassium and sodium.

Image of solid potassium hydroxide

Aqueous Solutions (Frame 17)

The previously 301 volt battery of the Royal Institution consisted of 24 copper and zinc plates of 12 inches square, 100 plates of 6 inches square, and 150 of 4 inches square. In 1808 Humphry Davy used this on saturated aqueous solutions of potash (KOH) and soda (NaOH). When he ran such high voltage through water, he found that he was able to split water into hydrogen and oxygen while observing a great deal of effervescence or bubbling and heat. The decomposition of water is shown below in the oxidation and reduction half-cells.

Cathode (reduction): 2H+(aq) + 2e → H2(g), Anode (oxidation): 2H2O(l) → O2(g) + 4H+(aq) + 4e (source: external link: http://en.wikipedia.org/wiki/Electrolysis_of_water)

Molten Poltash (Frame 18)

Davy had found that immersing his samples in water presented a problem as the water was electrolyzed more easily than the alkalis. He then decided to try melting potash instead. He produced a hot flame by applying a stream of oxygen gas from a gasometer onto the flame of an alcohol lamp, and thus used it to melt potash on a platina spoon. This seemed to succeed and maintain the potash in a molten state and thus allow him to run an electrical current through the sample.

To run the electric current through, the platina spoon was connected to the positive end of the battery consisting of 100 plates of 6 inches square. A platina wire in the spoon connected to the negative side.

In its molten state, the potash was a very strong conductor of electric current. A very intense light was emitted by the negative wire and also fire was produced at the point of contact between the wire and the potash, which Davy believed to result from the presence of some combustible material at that point.

Moist Potash (Frame 19)

Davy then used a small piece of pure potash exposed to the air to gather moisture in order to conduct electric current. He placed this potash on an insulated disc of platina connected to the negative side of the battery composed of 250 plates of 6 and 4 square inches. A platina wire connected to the positive side was placed in contact with the upper surface of the potash.

Small globules with a metallic luster and characteristics similar to mercury appeared, quite unlike melted potash. Some combusted and exploded, while others were tarnished and covered with a white film.

European Rivalry and Napoleon's Response (Frame 20)

1808 was also the time of the Peninsular War, when an alliance of Britain, Spain, and Portugal was combating the French occupation of the Iberian peninsula. There was consequently a strong rivalry between Britain and France, and Napoleon, who had some interest in science (he had been examined at the Ecole Militaire by Laplace), responded to the accomplishments of the English Royal Institution by providing a 650 volt battery to French scientists, which consisted of 600 1-kilogram copper plates and 600 3-kilogram zinc plates. He primarily funded the scientific endeavor, which cost 20,000 francs, while Gay-Lussac was the actual scientist in charge of the operation.

Napoleon once visited the laboratory, and before any attendants could stop him, placed the wires under his tongue because he wanted to try the taste of two metals coming in contact. He received a strong shock, and after recovering, left the laboratory without a remark and never spoke about it again. The Royal Institution would eventually obtain an even stronger 2200 volt battery. Davy also discovered the elements barium, boron, calcium, and magnesium in 1808.

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