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Q.(a) What is meant by demineralized water?
(b) Give the chemical reactions to justify the amphoteric nature of water.
Manipur CohsemCouncil of Higher Secondary Education, Manipur (Higher Secondary 1st Year) 2023Subjective· 3mImportance★★★★★
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Start your 14-day free trial to unlock the full solution →Demineralized water is water with all dissolved mineral ions removed (by ion exchange); water is amphoteric because it can donate a proton (act as an acid) or accept a proton (act as a base) depending on what it reacts with.
- Demineralized water: Demineralized (or deionised) water is water from which virtually all dissolved mineral salts and ions -- such as Ca2+, Mg2+, Na+, K+, Cl-, SO4^2-, HCO3- -- have been removed. This is typically achieved by passing water through ion-exchange resins (a cation-exchange resin that replaces metal cations with H+, followed by an anion-exchange resin that replaces anions with OH-, the H+ and OH- then combining to give pure H2O). Demineralized water is used where mineral-free water is essential, e.g. in laboratories and certain industrial processes.
- Amphoteric nature of water: Water is described as amphoteric (or amphiprotic) because, according to the Bronsted-Lowry acid-base concept, it can behave as EITHER an acid (proton donor) or a base (proton acceptor), depending on the other species it is reacting with. Water acting as an ACID (donates a proton, H+): H2O + NH3 -> NH4+ + OH- (Here water gives up a proton to ammonia, so water is the acid and ammonia is the base.) Water acting as a BASE (accepts a proton, H+): H2O + HCl -> H3O+ + Cl- …
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