Variable oxidation states of Transition Elements 0.0 / 5 ? ChemistryTransition metalsA2/A-levelAQA Created by: simran sandhuCreated on: 26-03-14 18:48 When does Potassium Manganate (VII) act as an oxidising agent? When it oxidises Fe to Fe What is the change in its oxidation number? In acidic solution. The oxidation number falls from +7 to +2 1 of 9 Why can we not use HCl as an alternative to sulfuric acid in the reaction between potassium manganate (VII) and Fe Ions? HCl contains Cl ions which would be oxidised by MnO ions. The manganate ions must be used only to oxidise Fe ions 2 of 9 When does the oxidation of lower oxidation states of transition metal ions occur and why? In alkaline solution because there is a tendency to form negative ions. Since oxidation is loss, it is easier for negatively charged species to do so 3 of 9 How can you prevent transition metals with low oxidation states from being oxidised by air? Keep them in acidic solution 4 of 9 How do you oxidise a transition metal to a high oxidation state? Add alkali followed by an oxidising agent 5 of 9 What are the colours of the three most important oxidation states of chromium? Cr(II) is blue, Cr(III) is green and Cr(VI) is yellow/ orange 6 of 9 What is the most stable oxidation state of chromium in aqueous solution? Chromium(III) 7 of 9 What is the colour of the complex formed when an excess of ammonia is added to a solution of cobalt(II) ions? Brown 8 of 9 Why must Cu Ions be protected from air? Because they have a low oxidation state and can therefore be oxidised by air 9 of 9
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