Chemical equation
Oxidant (oxidizing)+reducing agent (reducing) → Reduction product + Oxidation product Oxidation: oxidant>oxidation product Reducibility: reducing agent>reduction product This rule is applicable to any Δ Reaction of G<0 (i.e., the reaction that can be spontaneously carried out in this environment) All are valid without any exception. Oxidant -- electron gain -- valence reduction -- reduction -- occurrence Reduction reaction --Reduction product reductant -- electron loss -- valence rise -- oxidation -- occurrence oxidation reaction --Oxidation product Unfounded In the same reaction Oxidant ， reducing agent judge Spontaneous reaction in The oxidizability of oxidant can be weaker than or even far weaker than that of reducing agent（ Middle school students believe that oxidants must be more oxidizing than reducers, but this cognition is actually completely wrong, There is no relationship between oxidizability of oxidant and oxidizability of reducing agent) For example, hydrogen peroxide is far more oxidizing than chlorine, and its oxidation of chlorine to perchloric acid can be carried out spontaneously (when the standard electrode potential difference exceeds 0.2, the redox reaction can be carried out completely): (Standard Electrode potential ：H two O two —1.77—H two O，Cl two —1.36—Cl - ，ClO four - —1.39—Cl two ）However, the reaction of the two is that the former is oxidized: H two O two + Cl two → 2HCl + O two This is because most redox reactions have kinetic barriers
Metal mobility sequence
- one
For metal reducing agents, the reducibility of metal elements is generally the same as Metal mobility The order is consistent, that is, the more behind the metal, the less likely it is to lose electrons, and the weaker the reducibility. Metal activity order (common elements): K>Ca>Na>Mg>Al>Mn>Zn>Cr>Fe>Ni>Sn>Pb>(H)>Cu>Hg>Ag>Pt>Au - two
Metal cations in 25 ℃, pH=0 aqueous solution Intermediate oxidizing order Li + <Cs + <Rb + <K + <Ca 2+ <Na + <Mg 2+ <Al 3+ <Mn 2+ <Zn 2+ <Cr 3+ <Fe 2+ <Ni 2+ <Sn 2+ <Pb 2+ <(H + )<Cu 2+ < Fe 3+ <Hg two 2+ <Ag + <Hg 2+ <Pt 2+ <Au 3+
- three
be careful Fe, Sn, Pb, Hg correspond to Fe respectively 2+ 、Sn 2+ 、Pb 2+ ，Hg two 2+ Not Fe 3+ 、Sn 4+ 、Pb 4+ 、Hg 2+ (Especially Hg, many secondary school teaching assistants mistakenly think it corresponds to mercury ion)
Non metallic activity sequence (common elements)
- one
F in 25 ℃, pH=0 aqueous solution two >Cl two >O two >Br two >I two >S eight
- two
F in 25 ℃, pH=14 aqueous solution two >Cl two >Br two >I two >O two >S eight
- three
atom (or simple substance) oxidizability gradually weakens, corresponding anion reducibility increases 25 ℃, reducibility in aqueous solution with pH=0: H two S>I - >Br - >H two O>Cl - >Reducibility in HF25 ℃, pH=14 aqueous solution: S 2- >I - >Br - >OH - >Cl - >F - Supplement: Fe is often ignored in general teaching materials of non-metallic oxidation sequence 3+ , focusing on Fe, so the order of adding it is Cl two > Br two > Fe 3+ >I two >S eight [1]
Reaction conditions
When different oxidants react with the same reducing agent respectively, if the oxidation products have the same valence state, it can be judged according to the difficulty of reaction conditions. The easier the reaction is, the stronger the oxidizer is.
For example: 16HCl (concentrated)+2KMnO four →2KCl+2MnCl two +8H two O+5Cl two (g)
4HCl (concentrated)+MnO two — (Heating) → MnCl two +2H two O+Cl two (g)
4HCl(g)+O two - (Heating, CuCl two Catalyst) → 2H two O+2Cl two （g）
Oxidation: KMnO four >MnO two >O two [1]
But it may not be correct , because The more oxidizing substances may be more difficult to react due to the kinetic barrier, or the more reversible reaction may lead to the equilibrium direction Δ G> Move in the direction of 0
The valence of oxidation products
When reducing agents containing variable valence elements act on different oxidants under similar conditions, the oxidizability of oxidants can be judged according to the valence state of oxidation products, such as:
2Fe+3Cl two - (ignition) → 2FeCl three
Fe+S - (heating) → FeS
Oxidation: Cl two >S [1]
But it may not be correct , e.g. F two Only oxidize Os to+6 valence, O two Can be oxidized to+8 valence
periodic table of ele ments
- one
with Main family element (From top to bottom) The oxidation of non-metallic atoms (or simple substances) gradually weakens, and the corresponding anion reduction gradually increases. The reducibility of metal atoms gradually increases, and the corresponding cationic oxidation gradually weakens - two
Same period main family The element (from left to right) elemental reducibility gradually weakens, the oxidizability gradually increases, the cationic oxidizability gradually increases, and the anionic reducibility gradually weakens [1] 。
- three
Main family elements of the same period Hydrate of the highest valence oxide (only from left to right, Cannot compare up and down or diagonally ）The stronger the acidity, the stronger the oxidation of the corresponding element, the stronger the alkalinity, and the stronger the reduction of the corresponding element [1]
- four
- five
The electrode of the primary cell reacts with two different metals Primary battery The two poles of. The negative metal is the electrode from which electrons flow, positive electrode Metal is the pole into which electrons flow [1] 。 Its reducibility is generally: negative metal>positive metal (counter example: iron and copper in concentrated nitric acid) - six
The greater the concentration of substances with oxidizing (or reducing) properties, the stronger their oxidizing (or reducing) properties, and vice versa [1] 。
- seven
Generally speaking, the valence state of the elements in the highest valence state is only oxidizing, the lowest valence state is only reducing, and the intermediate valence state is both oxidizing and reducing. Generally, when it is in the highest valence state, its oxidizability is the strongest. With the reduction of the valence, its oxidizability decreases and its reducibility increases [1] 。 But there are also counterexamples, For example, in acidic aqueous solution, from 0 to the highest valence, the oxidizability of phosphorus thiochloride increases with the decrease of the valence
1. C is reducing agent CuO is oxidizing agent
Equation 1 2. C is reducing agent SiO2 is oxidizing agent
Equation 2
