File:125. Хемиски чај (оксидациски состојби на ванадиумот).webm

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Chemist’s tea (oxidation states of vanadium)

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English: In a aqueous solution of ammonium metavanadate and hydrochloric acid where hydrogen peroxide is added, a peroxo complex of vanadium(V) is formed having a reddish-brown color. The solution is heated to about 80ºC while stirred. Then, a tea bag containing granules of Devarda's alloy (an alloy of aluminum, copper, and zinc) is immersed. This alloy serves as a reducing agent in the subsequent reactions. Besides reacting with the vanadium ions, the alloy also reacts with the hydronium ions in the solution, producing gaseous hydrogen. Aluminum plays the main reducing role among the metals in the alloy, while there is lot less zinc and the copper does not participate in the reaction directly, due to its reduction potential.

After a few minutes of adding the alloy to the solution, a gradual change in color from reddish-brown to blue, then green, and finally violet is observed. These colors correspond to the change in the oxidation state of vanadium, from the peroxo complex of vanadium(V), VO2+ oxovanadium(IV) (vanadyl), V3+, and V2+ ions, respectively.

The experiment was performed by Prof. PhD Miha Bukleski. The planning of the experiment also included the Prof. Emeritus PhD Vladimir Petruševski, Prof. PhD Marina Stojanovska and the student Mihail Trajkov, Department of Chemistry, FNSM, Ss. Cyril and Methodius University, Skopje, Macedonia.
Македонски: Во воден раствор од амониум метаванадат и хлороводородна киселина на кој е додадено мало количество водород пероксид се образува пероксо комплекс на ванадиум(V) кој има црвено-кафеава боја. Растворот се загрева до околу 80 °C, при постојано мешање. Потоа во него се потопува ќесичка за чај во која се наоѓаат гранули од Девардова легура (легура од алуминиум, бакар и цинк). Оваа легура претставува редукциско средство во реакциите кои следат. Покрај реакцијата со јоните на ванадиум, легурата реагира и со хидрониум јоните во растворот при што се образува гасовит водород. Главната редукциска улога од металите во легурата ја има алуминиумот, додека цинкот е помалку застапен, а бакарот со оглед на неговиот редукциски потенцијал, не учествува директно во реакцијата.

По неколку минути од додавањето на легурата кон растворот се забележува постепена промена на бојата од црвено-кафеава кон сина, па зелена и на крај виолетова. Овие бои се должат на промената на оксидациската состојба на ванадиумот, пероксо комплекс на ванадиум(V), VO2+ оксованадиум(IV) (ванадил), V3+ и V2+ јоните, соодветно.

Експериментот е изведен од проф. Миха Буклески. Во планирањето на опитот исто така биле вклучени пензионираниот проф. д-р Владимир Петрушевски, проф. д-р Марија Стојановска и студентот Михаил Трајков, Институт за хемија, ПМФ, УКИМ, Скопје, Македонија.
Date
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Author Deni Ingilizovski


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current19:36, 13 July 20241 min 30 s, 1,920 × 1,080 (13.71 MB)Kiril Simeonovski (talk | contribs)Uploaded a work by Deni Ingilizovski from {{Own work}} with UploadWizard

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VP9 1080P 1.69 Mbps Completed 20:50, 13 July 2024 55 min 24 s
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