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Influence of Medium to Redox Reactions

 

Among Redox reactions it was marked out the group of processes where composition of oxidation and reduction processes products depend on medium (for example, reactions with Potassium Permanganate KMnO4, Potassium Dichromate K2Cr2O7 ( Table 12).

Example 1. KMnO4 + NaI + H2SO4

or K1+Mn7+O2-4 + Na1+I1- + H1+2S6+O2-4

Presence of H2SO4 (diluted) determines an acidic medium. Oxidizing agent is Mn7+ in acidic medium gained 5 electrons (see Table 12). Reducing agent is I-:

Mn7+ + 5 Mn2+ 2 (reduction);
2I- - 2 I2 5 (oxidation).

Products of reduction or oxidation and ions which do not change oxidation number in reaction are connected with ions of substance determined the medium of reaction:

Mn2++ SO42- MnSO4; 2K+ + SO42- K2SO4;

2Na+ + SO42- Na2SO4; 2H+ + O2- H2O.

So, in total:

2KMnO4+10NaI+8H2SO4=2MnSO4+5I2+K2SO4+5Na2SO4+8H2O.

Table 12. Influence of Medium to Composition of products of Redox reactions products

Compound and its function in redox reaction Medium Scheme of process Typical products
    Oxidizing agent KMnO4   Acidic (H+, pH<7) Mn7++5 Mn2+ Salts of Mn2+ and residue of acid determined medium
Alkaline (OH-, pH>7) Mn7++1 Mn6+ Salts of Manganic acid (H2MnO4) and alkali determined medium
Neutral (H2O) Mn7++3 Mn4+ MnO2
Oxidizing agent MnO2 Acidic (H+, pH<7) Mn4++2 Mn2+ Salts of Mn2+ and residue of acid determined medium
Oxidizing agent K2Cr2O7 Acidic (H+, pH<7) Cr6+ + 3 Cr3+ Salts of Cr3+ and residue of acid determined medium
Oxidizing agent H2O2 Acidic (H+, pH<7) O1-+1 O2- H2O
Reducing agents - Compounds included r3+ Alkaline (OH-, pH>7) r3+-3 Cr6+ Salts of Chromic acid (H2CrO4) and alkali determined medium
Reducing agents - Amphoteric metals in free state (Zn, Al, Be) Alkaline (OH-, pH>7) Zn02 Zn2+ Al0 3 Al3+ Be0 2 Be2+ Salts included alkaline and anions [Zn(OH)4]2-, [Al(OH)6]3-, [Be(OH)4]2- respectively

Date: 2015-01-12; view: 788


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