Sodium amalgam
From Wikipedia, the free encyclopedia
Sodium amalgam, with the common formula Na(Hg), is an alloy of mercury and sodium. The term amalgam is used for alloys, intermetallic compounds, and solutions (both solid solutions and liquid solutions) involving mercury as a major component. Sodium amalgams are often used in reactions as strong reducing agents with better handling properties compared to solid sodium. They are less dangerously reactive toward water and in fact are often used as an aqueous suspension.
Sodium amalgam was used as a reagent as early as 1862.[1] A synthesis method was described by J. Alfred Wanklyn in 1866.[2]
No particular formula is assigned to "sodium amalgam". Na5Hg8 and Na3Hg are well defined compounds. In sodium amalgams, the Hg-Hg distances are expanded to around 5 Å vs. about 3 Å for mercury itself.[3] Usually amalgams are classified on the weight percent of sodium. Amalgams with 2% Na are solids at room temperature, whereas some more dilute amalgams remain liquid.[4]
Preparation
| External videos | |
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| Demonstration and commentary on the preparation of sodium amalgam | |
 via YouTube | |
 Mixing sodium with mercury (31 December 2018), by NileRed |
Metallic sodium dissolves in mercury exothermically, i.e. with the release of heat, therefore, formation of sodium amalgam is famously dangerous for generating sparks.[5] The process causes localised boiling of the mercury and for this reason the formation is usually conducted in a fume hood and often performed using air-free techniques, such as synthesis under anhydrous liquid paraffin. Sodium amalgam may be prepared in the laboratory by dissolving sodium metal in mercury or the reverse.[6][7][8] Sodium amalgams can be purchased from chemical supply houses.