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⁺O^2-₄ + Na¹⁺I^1- + H¹⁺₂S⁶⁺O^2-₄ ®

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⁺+ SO₄^2- ® MnSO₄; 2K⁺ + SO₄^2-® K₂SO₄;

2Na⁺ + SO₄^2- ® Na₂SO₄; 2H⁺ + O^2- ® 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 Сr3+	Alkaline (OH-, pH>7)	Сr3+-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)	Zn0–2 ®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: 1043