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:''Not to be confused with Carbolic acid, an antiquated name for phenol.'' :''Carbonic acid is also an archaic name for carbon dioxide.'' | Section2 = }} Carbonic acid is a chemical compound with the chemical formula H2CO3 (equivalently OC(OH)2). It is also a name sometimes given to solutions of carbon dioxide in water (carbonated water), because such solutions contain small amounts of H2CO3. In physiology, carbonic acid is described as ''volatile acid'' or ''respiratory acid'', because it is the only acid excreted as a gas by the lungs.〔(Acid-Base Physiology 2.1 - Acid-Base Balance ) by Kerry Brandis〕 Carbonic acid, which is a weak acid, forms two kinds of salts, the carbonates and the bicarbonates. In geology, carbonic acid causes limestone to dissolve producing calcium bicarbonate which leads to many limestone features such as stalactites and stalagmites. The long-held belief that carbonic acid could not exist as a pure compound has reportedly been recently disproved by the preparation of the pure substance in both solid and gas form by University of Innsbruck researchers.〔("International first: Gas-phase carbonic acid isolated" ), phys.org, Jan 11, 2011〕 ==Chemical equilibrium== When carbon dioxide dissolves in water it exists in chemical equilibrium producing carbonic acid:〔 :CO2 + H2O H2CO3 The hydration equilibrium constant at 25 °C is called Kh, which in the case of carbonic acid is ()/() ≈ 1.7×10−3 in pure water〔Housecroft and Sharpe, ''Inorganic Chemistry'', 2nd ed, Prentice-Pearson-Hall 2005, p.368.〕 and ≈ 1.2×10−3 in seawater. Hence, the majority of the carbon dioxide is not converted into carbonic acid, remaining as CO2 molecules. In the absence of a catalyst, the equilibrium is reached quite slowly. The rate constants are 0.039 s−1 for the forward reaction (CO2 + H2O → H2CO3) and 23 s−1 for the reverse reaction (H2CO3 → CO2 + H2O). Carbonic acid is used in the making of soft drinks, inexpensive and artificially carbonated sparkling wines, and other bubbly drinks. The addition of two molecules of water to CO2 would give ''orthocarbonic acid'', C(OH)4, which exists only in minute amounts in aqueous solution. Addition of base to an excess of carbonic acid gives bicarbonate (hydrogen carbonate). With excess base, carbonic acid reacts to give carbonate salts. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Carbonic acid」の詳細全文を読む スポンサード リンク
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