Chemical Engineering in Daily Life - Question 10 - Standard answers available
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This post was last edited by yjqin1 on 2015-8-20 at 19:31. Kids who are mischievous as children can grow up to become chemists; such mischievousness shouldn’t be the same as that of silly kids. One of the mischievous acts was to take an adult’s flashlight, remove the battery from it, add some salt, and dissolve it in a bowl to create a sodium chloride solution. Then, using the battery, cathode wire, and anode wire, they carried out a scientific experiment to electrolyze the sodium chloride solution. Once the craving to be a chemist was satisfied and the battery was secretly put back, of course the flashlight no longer shone as brightly, and often the child would get scolded by the adults at night. During the experiment, a phenomenon was observed: as bubbles were formed, the water around the anode turned green, and more bubbles appeared at the cathode. It’s just that the originally clear saline solution became dirty. Please explain why?
This post was last edited by zdl1966 on 2015-8-17 at 20:06. Anions (chloride ions and hydroxide ions) are present around the anode; chlorine gas is generated, and when this chlorine gas dissolves in water it forms salts and acids, which is why the color turns green. Around the cathode are cations (sodium ions, hydrogen ions), and hydrogen gas is produced. Since there is plenty of water, there are many hydrogen ions, which in turn results in more hydrogen gas and more vapor bubbles. I don’t understand why it gets dirty
Standard answer: 1. The saltwater turns green because molecular chlorine produced by the reaction dissolves in it. Of course, hypochlorite also has a slight color. Recently we have been working on research on dechlorination using gas membrane methods, so I have a fairly in-depth understanding of it. The surface of saltwater becomes dirty because the electrolysis of saltwater produces chlorine and hydrogen, which escape in the form of tiny bubbles. Many tiny bubbles are generated, which in turn results in a foam separation effect. The so-called foam separation is an application of a surface phenomenon discussed in physical chemistry. If there are some impurities with low surface tension in the aqueous solution, they adsorb at the water-air interface; the polar groups in their molecules remain in the water, while the non-polar groups end up at the air-water interface. If there is movement at the air-water interface, these low surface activity substances will move along with the interface. For example, air bubbles rise due to buoyancy, and substances with low surface tension also rise. Water contains more or less some organic substances, such as humic acids; the concentration of these impurities is very low, for example, less than 1 mg/L. However, due to the magnifying effect caused by the bubbles, they remain on the surface of the water temporarily, making it appear dirty.