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Chemistry 2.6
AS edexcel chemistry - redox
Question | Answer |
---|---|
What is a redox reaction and a disproportionation reaction? | Redox - where one substance is oxidised and the other is reduced. Disproportionation - a redox reaction where an element in a single species is simultaneously oxidised and reduced |
What is reduction and oxidation? | Reduction - the loss of oxygen, the gain of hydrogen, the gain of electrons (RIG). Oxidation - the gain of oxygen, combustion, the loss of hydrogen, the loss of electrons (OIL) |
What is an oxidising agent? | An agent that oxidises another species by removing electrons, and the agent is simultaneously reduced |
What is a reducing agent? | An agent that reduces another species by donating electrons, and the agent is simultaneously oxidised |
How do you complete complex and simple half equations and turn them into full ionic equations? | Balance atoms and charges. Include state symbols. Simple: balance just with electrons. Complex (acid): balance O with H2O, balance H with H+, balance charge with e-. Ensure number of electrons in half equations are equal before adding |
What is oxidation number? | The formal number of electrons gained or lost by an atom of an element in a compound if the compound is considered to be wholly ionic |
What does an increase/ decrease in oxidation number mean? | Increase - substance has been oxidised, decrease - substance has been reduced |
What are the rules of oxidation numbers? | Uncombined element=0. Monatomic ion=charge on ion. Sum in a neutral compound=0. Sum in a polyatomic ion=charge on ion. Group 1 = +1. Group 2=+2. F=-1. H= +1 (except with a metal). O=-2 (except superoxide, peroxide or with fluorine) |
What are some steps to remember with oxidation numbers? | Ignore stoichiometry, oxidation numbers can be fractions, give the sign then the number |
What are the oxidation numbers of the elements in: (NH4)2Cr2O7 | N= -3. H=+1. Cr = +6. O = -2 |
What are the oxidation numbers of the elements in: NaOH | Na = +1. O = -2. H = +1 |
What is the number of electrons in a half equation equal to? | The change in oxidation number of the element |
What are some real -life examples of oxidation and reduction? | Aerobic respiration: oxygen reduced from 0->-2. Rusting: oxygen reduced from 0->-2, iron oxidised from 0->2. Combustion: oxygen is reduced, other reactant is oxidised. Batteries: Zn+CuSO4->ZnSO4+ Cu. displacement reaction, Zn oxidised, Cu reduced |
What is the half equation for NO3- -> NO2- | NO3 - + 2H+ + 2e -> NO2- + H2O |