Tin, Sn2+, Sn4+
Most common oxidation states: +2, +4
Density 7.30 g/cm3
Characteristics: Metallic tin is soft and malleable. It slowly dissolves in dilute nonoxidizing acids or more readily in hot concentrated HCl. It reacts with HNO3 to form metastannic acid, H2SnO3, a white substance insoluble in alkalies or acids. In neutral or only slightly acidic solutions, zinc displaces tin from its compounds, forming the metal.
Characteristic reactions of Sn2+ and Sn4+:
In aqueous solutions, both tin(II) and tin(IV) exist as complex ions. Both tin(II) chloride and tin(IV) chloride tend to undergo hydrolyze and aged solutions of these salts become measurably acidic. Acid should be added to aqueous solutions of these compounds to prevent hydrolysis.
Tin(IV) chloride exists as a colorless liquid. It is soluble in organic solvents, and is a nonconductor of electricity, indicating that it is a molecular compound.
Tin(II) chloride is a strong reducing agent and is easily oxidized by atmospheric oxygen. Metallic tin is often added to solutions of SnCl2 to prevent this oxidation.
Although there is no visible reaction, tin(II) exists as the complex ion [SnCl4]2- and tin(IV) as the complex ion [SnCl6]2-.
Aqueous ammonia precipitates white Sn(OH)2 and white Sn(OH)4 with tin(II) and tin(IV), respectively.
Both precipitates, tin(II) hydroxide and tin(IV) hydroxide, dissolve in excess aqueous ammonia.
Sodium hydroxide also precipitates the hydroxides:
These precipitates dissolve in excess hydroxide:
In mildly acidic solution, sulfide precipitates SnS (brown) and SnS2 (light yellow):
SnS2 is soluble in basic solutions containing excess S2-, even in the presence of ammonia. It is also soluble in 6 M HCl:
SnS is soluble in 12 M HCl:
Reducing and Oxidizing Agents:
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