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2H2O + 2e- => H2 + 2OH- o Theupperequationshowstheoxidation(i.e.,lossofelectronsfromanatom)attheanodeand release of chlorine gas (i.e., Cl2). NOTE: Cl- is easier to oxidize than water, thus the product formed at the cathode is chlorine gas. o Thelowerequationshowsthereduction(i.e.,gainofelectronsbyanatom)atthecathodeand release of hydrogen gas (i.e., H2). NOTE: Water is easier to reduce than Na+ ions, thus the product formed at the cathode is hydrogen gas. o Posethequestion:"Giventhetwoequations(above),whatistheionicequationfortheoverall reaction?" (2Cl- + 2H2O => Cl2 + H2 + 2OH-) Assessment / Questions o Askthestudents:"Whydidthesaltmakethewatermoreconductivetoelectricity?"(Themolecules of salt dissociate into ions of opposite charges. It is the ions that render the water conductive to electricity. In our experiment, the Na+ and Cl- ions made it possible for the distilled water to conduct electricity.) o Askthestudents:"WouldsolidNaClconductelectricity?"(No.InasolidcompoundtheNa+orCl- ions are strongly attracted to each other; these ionic bonds cannot be broken by an electrical current.) o "WouldmoltenNaClconductelectricity?"(Yes.Inliquidform,theionicbondbetweentheNa+and Cl- ions is weakened and thus can become mobile and conduct electricity.) o "Wouldtapwaterconductelectricity?"(Yes.Thereareenoughionsintapwatertoconduct electricity.) Ask the students if they have heard the terms "soft water" and "hard water." Ask them to discover what types of ions are usually present in "hard water" (calcium and magnesium). Explain that "water softening" is major industry and ask if they can list reasons why this is the case. (Hard water requires more soap and detergent for laundering, cleaning and bathing because suds do not form well. The reaction between soap and hard water results deposits that make fabrics feel harsh and leave water spots on dishes and utensils. Mineral scale from hard water builds up in hot water appliances and industrial boilers, reducing energy efficiency and shortening appliance and equipment life.) o Anindependentresearchprojectcouldbeassignedthatfocusesonthewatersoftening process. A great website for this is the "Salt Institute" (http://www.saltinstitute.org). o OPTIONAL:ToaccessananimationdepictinghowioniccompoundssuchasNaCldissolvein water, visit Northland College (Minnesota)'s Department of Biology webpage (http://www.northland.cc.mn.us/biology/Biology1111/animations/dissolve.html). o OPTIONAL:Toaccessaninteractiveanimationdepictingtheinteractionofice,water,andasolute (e.g., salt), visit the "General Chemistry Online!" webpage, "Why does salt melt ice?" (http://antoine.frostburg.edu/chem/senese/101/solutions/faq/why-salt-melts-ice.shtml). o Besuretoraiseandlowerthetemperatureand"addsolute"byclickingonthebannerbelow the "dancing" water molecules. Ask students to explain how this animation relates to their experiment results. Vocabulary o anode: A positively charged electrode. o atom: A chemical unit, composed of protons, neutrons, and electrons, that cannot further break down by chemical means. o cathode: A negatively charged electrode. o compound: A pure substance composed of more than one element. o conductor: A substance or medium that conducts heat, light, sound, or especially an electric charge. o covalent bond: A chemical bond that involves sharing of electron pairs. o electrode: A solid electric conductor through which an electric current enters or leaves an electrolytic cell. o electron: A negatively charged subatomic particle with a mass of 0.00055 atomic mass units (AMU). By definition, one AMU is one-twelfth the mass of a carbon-12 atom. o ion: A charged particle. o ionic bond: An electrostatic interaction between a cation (+ charged ion) and an anion (- charged ion). o molecule: A pure substance which results when two or more atoms of a single element share electrons, forPDF Image | ELECTROLYSIS OF SALT WATER
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