Oxidation refers to the ability of a substance to obtain electrons.Substances and activities in high valence stateNon metallic simple substance(such as fluorine, chlorine, oxygen, etc.) are generally oxidizing, while substances in the low valence state generally haveReducibility。
Substances in high valence state are generally oxidizing, such as: some non-metallic simple substances: Otwo，Cltwo；Some high priced metals: Fe3+，MnOfour-wait.
Substance in low price state generally hasReducibility(For example: some metal elements（Middle schoolMetal elements only have reducibility,In fact, negative metals are very common）, partialNonmetalAnion: Br-，I-wait.
Substances in the intermediate valence state generally have both reducing and oxidizing properties (such as tetravalent sulfur)
Oxidant --- → reduction reaction --- → reduction product.Reduction reaction: get electrons, reduce the valence, and be reduced.
Reducing agent --- → oxidation reaction --- → oxidation product.Oxidation reaction: electron loss, valence rise, and oxidation.
Oxidability (ability to obtain electrons): oxidant>oxidation product.
Reducibility (ability to lose electrons): reducing agent>reducing product.
This rule holds true for any reaction with Δ G<0 in any environment (that is, a reaction that can occur spontaneously in this environment), without any exception (if there is more than one oxidation product or oxidant, the weighted average of oxidant is stronger than the weighted average of oxidation product, and so is the weighted average of reductant).
UnfoundedIn the same reactionOxidant，reducing agentJudgment.becauseSpontaneous reactioninThe 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): (StandardElectrode potential：HtwoOtwo—1.77—HtwoO，Cltwo—1.36—Cl-，ClOfour-—1.39—Cltwo）However, the reaction of the two is that the former is oxidized: HtwoOtwo+ Cltwo→ 2HCl + OtwoThis is because most of the thermodynamically feasible oxidation-reduction reactions have kinetic barriers
2. Comparison according to the sequence of material activity
(1) For metal oxidants, the oxidizability of metal cations is generally the same asMetal mobilityThe order is opposite, that is, the more behind the metal, the easier to get electrons, and the stronger the oxidation.
Li+<Cs+<Rb+<K+<Ca2+<Na+<Mg2+<Al3+<Mn2+<Zn2+<Cr3+<Fe2+<Ni2+<Sn2+<Pb2+<(H)<Cu2+<Fe3+<Hgtwo2+<Ag+<Hg2+<Pt2+<Au3+(Note Sn2+、Pb2+, not Sn4+、Pb4+）（Hg corresponds to Hgtwo2+Not Hg2+）
(3) The reducibility and oxidizability of metal elements are completely opposite, and the corresponding order is: K>Ca>Na>Mg>Al>Mn>Zn>Cr>Fe>Ni>Sn>Pb>(H)>Cu>Hg>Ag>Pt>Au
The oxidization of simple substances gradually weakens, and the corresponding anion reduction increases (note that the non-metallic nature of elements is not necessarily related to the oxidization of simple substances, and the above order is the oxidization of simple substances)
3. Judge according to 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)+2KMnOfour==2KCl+2MnCltwo+8HtwoO+5Cltwo(gas)
But it is not necessarily correct, because the more oxidizing substances may be more difficult to react due to kinetic barriers, or the greater degree of reversibility of the reaction may cause the balance to move in the direction of Δ G>0
4. Judge according to 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+3Cltwo- (ignition) → 2FeClthree
Fe+S - (heating) → FeS
Oxidation: Cltwo>S
But it may not be correct, for example: FtwoOnly oxidize Os to+6 valence, OtwoCan be oxidized to+8 valence
5. Judge according to the periodic table of elements
The oxidizability of non-metallic atoms (or simple substances) gradually weakens, and the reducibility of corresponding anions gradually increases.
The reducibility of metal atoms gradually increases, corresponding tocationOxidation gradually weakens
(2) Main family elements in the same cycle (from left to right)
The reducibility of the simple substance gradually weakens, and the oxidizability gradually increases
The oxidizing ability of cations is gradually enhanced, while the reducing ability of anions is gradually weakened.
6. Hydrate of the highest valence oxide of the main group elements in the same period (only from left to right, not up and down or oblique comparison)
The stronger the acidity, the stronger the oxidation of corresponding elements
The stronger the alkalinity, the stronger the reducibility of corresponding elements
7. Judging according to electrode reaction of primary battery
Consisting of two different metalsPrimary batteryThe two poles of.The negative metal is the electrode from which electrons flow,positive electrodeMetals are the poles into which electrons flow.
Its reducibility: negative metal>positive metal
8. Judge according to the concentration of the substance
The higher the concentration of oxidizing (or reducing) substances, the stronger their oxidizing (or reducing) properties, and vice versa.
9. Judge according to the valence of elements
Generally speaking, the variable valence elements are only oxidizing when they are in the highest valence state, reducing when they are in the lowest valence state, and oxidizing and reducing when they are in the middle valence state.Generally, when it is in the highest valence state, its oxidizability is the strongest. With the reduction of the chemical valence, its oxidizability decreases and its reducibility increases.However, there are also counter examples. For example, in acidic aqueous solution, from 0 to the highest valence, the oxidizability of phosphorus thiochloride increases with the decrease of the valence
Data comparison method
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Can also calculateElectrode potentialUnderstanding whether the oxidation reaction can be carried out spontaneously is also the most accurate judgment method.according toStandard electrode potentiometer, can also overturn some common mistakes.Otwo，CltwoAnd MnOtwoOxidation strength of 4HCl (concentrated)+MnOtwo=heating= MnCltwo+2HtwoO+Cltwo(Gas) 4HCl (rich)+Otwo=Heating, CuCl2 catalyst= 2HtwoO+2Cltwo(Qi) If we judge by the reaction, it will be confused.According to the difficulty of reaction, MnOtwo>Otwo>CltwoAlso know 2MnO+Otwo=heating= 2MnOtwoAccording to oxidant greater than oxidation product CltwoIn this way, there is no fixed number of oxidizability.And inStandard electrode potentialIt can be understood at a glance: Mn (IV) - (II) MnOtwo+4H++2e－=Mn2++2HtwoO 1.224 O(0)－(－II) Otwo+4H++4e－=2HtwoO 1.229 Cl(0)－(－I) Cltwo(g)+2e－=2Cl－1.35827 Can know Cltwo>Otwo>MnOtwoSince the oxidizability of the three is very close, it is possible to use any oxidant, which varies with the concentration of reaction conditions. Therefore, many reactions cannot explain the strength of oxidizability.Only according to specific data can we judge the degree of oxidation.
Oxidizing substances
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Oxidizing substance refers to a kind of substance with relatively active chemical properties that may not burn itself, but can release oxygen and may cause or promote the combustion of other substances.It usually refers to the materials with high valence atomic structure and the materials with dioxygen structure in inorganic compounds.It generally does not burn itself.
However, it can be carried out when encountering acid, being wet, strong heat, or contacting with other reducing substances and flammable substancesOxidative decomposition reaction, release heat and oxygen, cause combustion of combustible materials, and sometimes formExplosive mixture。《International Maritime Dangerous Goods Code》Oxidizing substances are classified as Class 5.1 dangerous goods.[1]There are oxidants and reducing agents in the oxidation reduction reaction.
