Oxidation :- The addition of oxygen/electronegative element to a substance or removal of hydrogen / electropositive element from a substance -- Loss of electrons by any species
* An increase in the oxidation number of the element in the given substance
Reduction :- removal of oxygen / electronegative element from a substance or addition of hydrogen / electropositive element to a substance -- Gain of electron by any species
*A decrease in the oxidation number of the element in the given substance
Redox :- When oxidation and reduction occur simultaneously
(Brain teaser:- in the equation 2Na + H2 --> 2NaH which is getting oxidised and which is getting reduced?)
Oxidation reactions :- Half reaction that involve loss of electrons are oxidation reactions
Redution reactions:- Half reactions that involve gain of electrons are called reduction reactions
Oxidising Agent :- A reagant which can increase the oxidation number of an elemet in a given substance . (They accept electrons and gets reduced itself)
Reducing Agent :- A reagant which lowers the oxidation number number of an elemt in a given substance. They donate electron to each of the elements interacting with it and gets oxidised itself.
Oxidation number :- It denotes the oxidation state of an element in a compound ascertained according to a set of rules formulated on the basis that electron pair in a covalent bond belongs entirely to more electronegative element.
Stock Annotation :- The oxidation number is expressed by putting a roman numeral representing the oxidation number in parenthesis after the symbol of the metal in the molecular formula
Displacement reactions :- In a displacement reaction, an ion (or an atom) in a compound is replaced by an ion ( or an atom) of another element.
(Important point :- Displacement reactions of chlorine, bromine and iodine using Fluorine are not generally carried out in aqueous solution)
Layer Test :- Identification of Br- and I- in laboratory using the reactions
i) Cl2 + 2KBr ----> 2 KCl + Br2
ii) Cl2 + 2KI ----> 2 KCl + I2
Disproportionation reactions:- Reactions where an element in one oxidation state is simultaneously oxidised and reduced.
Fractional oxidation numbers :- These , are not possible as elecrons are never shared/transferred in fractions, represent average oxidation state of the element.
Egs :- Carbon in Carbon suboxide ( C3O2)
Bromine in Tribromooctaoxide (Br3O8)
Sulphur in Tetrathinate ion (S4O6) 2-
(Illustration Brain teaser :- Why do the following reactions proceed differently?)
TITRATIONS
Permagnometry :-
*Reagant itself is intensely coloured
*MnO4- acts as self indicator
*first lasting tinge of pink colour appears at MnO4- concentration as low as 10^-6 mol dm^-3 ( 10 ^-6 mol/L)
*Ensures minimal 'overshoot' in colour beyond the equivalence poitn , the point where the reductant and oxidant are equal in terms of their mole stoichometry
Dichrometry :-
*(Cr2O7) -2 is not a self indicator
*oxidises the indicator substance diphenyamine just after the equivalence point to produce an intense blue colour thus signalling the end point.
Iodimetry :-
* On the fact that iodine itself gives an intense blue colour with starch and has a very specific reaction with thiosulphate ions (S2O3 ) 2-
* On addition of starch after the liberation of iodine from the reaction , an intense blue colour appears. This colour dissapears as soon as the iodine is consumed by the thiosulphate ions.
Redox Couple :- It is defined as having together the oxidised and reduced forms of a subtance taking part in an oxidation or reduction half reaction
Danielle Cell:- The set up for showing the procedure of copper and zinc redox couple ( NCERT pg 278 Part.II)
Electrode Potential :- The potential associated with each electrode is known as electrode potential
* It is a measure of the relative tendency of the active species in the process to reamin in the oxidised/reduced form.
Standard electrode potential :- If the concentration of each species is unity ( any gas appeards in the electrode reaction, it is confined to 1 atm) and the reaction is carried out in 298K , then potential of each electrode is said to be the Standard electrode potential.
* A negative standard potential means that the redox couple is a stronger reducing agent than the H+/H2 couple.
*A positive standard potential means that the redox xouple is a weaker reducing agent that the H+/H2 couple.
(check out page 279 NCERT part.II for detailed explanation)
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