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2

It's hard to pinpoint what the problem here is since I don't have the mentioned book to compare an answer with. The simplest way is write down half-reactions for reduction (red) and oxidation (ox) processes once you've assigned oxidation numbers (denoted above the symbols of the elements which are participating in a redox reaction), then balance the number ...

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Run everything one more cycle and you are totally safe. Copper is highly soluble in water, so it will entirely dissolve and go away, not contaminating your plates.

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A balanced equation must have a mass balance i.e., the masses should be equal on both sides and charges must be balanced as well. Oxidation number is just a way of book-keeping. Nothing fundamental there. $$\ce{Fe^2+ + Cr2O7 + 14H+ -> 2 Cr^3+ + Fe^3+ 7 H2O}$$ What are you forgetting? It is mass balanced. Does $\ce{Cr2O7}$ exist? Hint: It is potassium ...

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On negative oxidation states, in general Although it's usually a topic that's covered relatively late in a chemistry education, negative oxidation states for transition metals[1] are actually quite alright. On the Wikipedia list of oxidation states, there are quite a number of negative oxidation states. Some textbooks have tables which only show positive ...

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If there is an element in the reactants and it is not an element in the products then yes, oxidation or reduction has occurred. Acid-base reactions are pretty much non-redox reactions. But it is always handy to learn the oxidations numbers. Extra sources Do non-redox reactions exist?

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