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Water-reactive substances [1] are those that spontaneously undergo a chemical reaction with water, often noted as generating flammable gas. [2] Some are highly reducing in nature. [ 3 ] Notable examples include alkali metals , lithium through caesium , and alkaline earth metals , magnesium through barium .
Potassium metal can react violently with water producing KOH and hydrogen gas. 2 K(s) + 2 H 2 O(l) → 2 KOH(aq) + H 2 (g)↑ A reaction of potassium metal with water. Hydrogen is produced, and with potassium vapor, burns with a pink or lilac flame. Strongly alkaline potassium hydroxide is formed in solution.
Due to the strongly alkaline reaction conditions, aldehydes that have alpha hydrogen atom(s) instead undergo deprotonation there, leading to enolates and possible aldol reactions. Under ideal conditions the reaction produces 50% of both the alcohol and the carboxylic acid (it takes two aldehydes to produce one acid and one alcohol). [5]
The reaction between sodium hydroxide and some metals is also hazardous. Aluminium, magnesium, zinc, tin, chromium, brass and bronze all react with lye to produce hydrogen gas. Since hydrogen is flammable, mixing a large quantity of lye with aluminium could result in an explosion. Both the potassium and sodium forms are able to dissolve copper.
The exothermic reaction of potassium hydroxide with methanol leads in an equilibrium reaction to potassium methanolate and water (avoiding formation of highly inflammable hydrogen gas). In a continuous process the formed water must be removed permanently. [2] Kaliummethanolat aus Kaliumhydroxid und Methanol
Potassium hydride, KH, is the inorganic compound of potassium and hydrogen. It is an alkali metal hydride. It is a white solid, although commercial samples appear gray. It is a powerful superbase that is useful in organic synthesis. It is sold commercially as a slurry (~35%) in mineral oil or sometimes paraffin wax to facilitate dispensing. [3]
Potassium carbonate, formed from the hydroxide solution leaking from an alkaline battery. Aqueous potassium hydroxide is employed as the electrolyte in alkaline batteries based on nickel-cadmium, nickel-hydrogen, and manganese dioxide-zinc. Potassium hydroxide is preferred over sodium hydroxide because its solutions are more conductive. [20]
In pure water at the negatively charged cathode, a reduction reaction takes place, with electrons (e −) from the cathode being given to hydrogen cations to form hydrogen gas. At the positively charged anode, an oxidation reaction occurs, generating oxygen gas and giving electrons to the anode to complete the circuit.