Leveling effect (original) (raw)
水平化効果（すいへいかこうか、英: leveling effect）とは、溶媒に強い酸および強い塩基を加えてもその強さが溶媒によって決定され、見かけ上強さの差が隠される現象のことである。
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| dbo:abstract | Leveling effect or solvent leveling refers to the effect of solvent on the properties of acids and bases. The strength of a strong acid is limited ("leveled") by the basicity of the solvent. Similarly the strength of a strong base is leveled by the acidity of the solvent. When a strong acid is dissolved in water, it reacts with it to form hydronium ion (H3O+). An example of this would be the following reaction, where "HA" is the strong acid: HA + H2O → A− + H3O+ Any acid that is stronger than H3O+ reacts with H2O to form H3O+. Therefore, no acid stronger than H3O+ exists in H2O. For example, aqueous perchloric acid (HClO4), aqueous hydrochloric acid (HCl) and aqueous nitric acid (HNO3) are all completely ionized, and are all equally strong acids. Similarly, when ammonia is the solvent, the strongest acid is ammonium (NH4+), thus HCl and a super acid exert the same acidifying effect. The same argument applies to bases. In water, OH− is the strongest base. Thus, even though sodium amide (NaNH2) is an exceptional base (pKa of NH3 ~ 33), in water it is only as good as sodium hydroxide. On the other hand, NaNH2 is a far more basic reagent in ammonia than is NaOH. The pH range allowed by a particular solvent is called the acid-base discrimination window. (en) L'effetto livellante è il fenomeno per cui acidi o basi forti (cioè presenti in soluzione interamente sotto forma di ioni liberi solvatati) presentano nel solvente acqua tutti valori estremamente alti delle costanti di equilibrio, tali che ai fini pratici possono considerarsi ognuno egualmente forte in ambiente acquoso. Per avere un'idea degli ordini di grandezza della Ka dei principali acidi in solvente acquoso a 25 °C, ecco i valori delle relative coppie acido-base: * Acido perclorico HClO4-ClO4- → Ka = 1010 * Acido iodidrico HI-I- → Ka = 1010 * Acido cloridrico HCl-Cl- → Ka = 107 * Acido solforico H2SO4-HSO4- → Ka = 103 * Acido nitrico HNO3-NO3- → Ka = 102 * Ione idronio H3O+-H2O → Ka = 102 In ultima analisi, si può affermare che gli ioni H3O+ generati da acidi totalmente dissociati e ioni OH- generati da basi forti sono praticamente i fattori "livellanti" generati dal solvente acqua, in quanto uguale è l'entità delle dissociazioni in oggetto. È bene inoltre ricordare che in solventi con basicità diversa dall'acqua i relativi equilibri di dissociazioni sono ben diversi: ad esempio in acido formico (HCOOH) HClO4 risulta più forte di HBr (in acqua si ha invece l'effetto livellante) perché, essendo scarsissima la tendenza dell'acido formico ad accettare protoni, la forza acida dipende quasi esclusivamente dalla capacità propria dell'acido a cedere protoni. In ammoniaca liquida, essendo un solvente fortemente basico, anche acidi che in soluzione acquosa risultano debolmente dissociati si comportano da acidi forti. (it) 水平化効果（すいへいかこうか、英: leveling effect）とは、溶媒に強い酸および強い塩基を加えてもその強さが溶媒によって決定され、見かけ上強さの差が隠される現象のことである。 (ja) Вирівнювальний ефект (рос. нивелирующее влияние, англ. leveling effect) — 1. * Вирівнювання сили основ Бренстеда протогенними розчинниками. 2. * Зменшення величини дії кожної наступної групи при послідовному заміщенні атомів H біля реакційного центра. (uk) 拉平效应，又稱水平效應、齊平效應、流平效應、調平效應、校平效應、平準效應（英語：Leveling effect），指酸和碱的性质受到溶液种类影響的现象。例如在水溶液中，所有比水合氢（H3O+）酸度高的酸都要降到水合氢的酸度；同理，在水溶液中，所有碱性比（OH-）高的碱都会降到（OH-）的碱度。 水的拉平效应是由于它具有高介电常数和强接收质子的倾向。不同溶液对酸和碱的流平作用不同；是因为它们和酸-碱的质子相互作用不同；在此基础上；溶液可分为四种类型： 1. * 易受型溶液。它们具有很强接受质子的倾向，即水，酒精和液氨等。 2. * 易生型溶液。它们具有产生质子的倾向；即水，液体氯化氢，冰醋酸等。 3. * 二性溶液。它们具有上述二种溶液的性质；即水，氨和乙醇等。 4. * 非质子溶液。它们既不贡献也不接受质子；即苯，四氯化碳，二硫化碳等。 对某一特定溶液所允许的pH值范围，称为酸-碱区分窗口。 (zh) |
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| rdfs:comment | 水平化効果（すいへいかこうか、英: leveling effect）とは、溶媒に強い酸および強い塩基を加えてもその強さが溶媒によって決定され、見かけ上強さの差が隠される現象のことである。 (ja) Вирівнювальний ефект (рос. нивелирующее влияние, англ. leveling effect) — 1. * Вирівнювання сили основ Бренстеда протогенними розчинниками. 2. * Зменшення величини дії кожної наступної групи при послідовному заміщенні атомів H біля реакційного центра. (uk) 拉平效应，又稱水平效應、齊平效應、流平效應、調平效應、校平效應、平準效應（英語：Leveling effect），指酸和碱的性质受到溶液种类影響的现象。例如在水溶液中，所有比水合氢（H3O+）酸度高的酸都要降到水合氢的酸度；同理，在水溶液中，所有碱性比（OH-）高的碱都会降到（OH-）的碱度。 水的拉平效应是由于它具有高介电常数和强接收质子的倾向。不同溶液对酸和碱的流平作用不同；是因为它们和酸-碱的质子相互作用不同；在此基础上；溶液可分为四种类型： 1. * 易受型溶液。它们具有很强接受质子的倾向，即水，酒精和液氨等。 2. * 易生型溶液。它们具有产生质子的倾向；即水，液体氯化氢，冰醋酸等。 3. * 二性溶液。它们具有上述二种溶液的性质；即水，氨和乙醇等。 4. * 非质子溶液。它们既不贡献也不接受质子；即苯，四氯化碳，二硫化碳等。 对某一特定溶液所允许的pH值范围，称为酸-碱区分窗口。 (zh) Leveling effect or solvent leveling refers to the effect of solvent on the properties of acids and bases. The strength of a strong acid is limited ("leveled") by the basicity of the solvent. Similarly the strength of a strong base is leveled by the acidity of the solvent. When a strong acid is dissolved in water, it reacts with it to form hydronium ion (H3O+). An example of this would be the following reaction, where "HA" is the strong acid: HA + H2O → A− + H3O+ The pH range allowed by a particular solvent is called the acid-base discrimination window. (en) L'effetto livellante è il fenomeno per cui acidi o basi forti (cioè presenti in soluzione interamente sotto forma di ioni liberi solvatati) presentano nel solvente acqua tutti valori estremamente alti delle costanti di equilibrio, tali che ai fini pratici possono considerarsi ognuno egualmente forte in ambiente acquoso. Per avere un'idea degli ordini di grandezza della Ka dei principali acidi in solvente acquoso a 25 °C, ecco i valori delle relative coppie acido-base: (it) |
| rdfs:label | Leveling effect (en) Effetto livellante (it) 水平化効果 (ja) 拉平效应 (zh) Вирівнювальний ефект (uk) |
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