Sodium (Na) and water
Sodium and water: reaction mechanisms, environmental impact and health effects
|For billions of years sodium is washed out from rocks and soils, ending up in oceans, where it may remain for about 50.106 years. Seawater contains approximately 11,000 ppm sodium. Rivers contain only about 9 ppm. |
Drinking water usually contains about 50 mg/L sodium. This value is clearly higher for mineral water. In soluble form sodium always occurs as Na+ ions.
Elementary sodium reacts strongly with water, according to the following reaction mechanism:
2Na(s) + 2H2O → 2NaOH(aq) + H2(g)
A number of examples of water solubility of sodium are available. De most familiar sodium compounds is sodium chloride (NaCl), otherwise known as kitchen salt. At 20oC solubility is 359 g/L, in other words adequately water soluble. Solubility is nearly temperature independent. Sodium carbonate (Na2CO3) is also adequately water soluble. Solubility is 220 g/L at 20oC.
Sodium compounds naturally end up in water. As was mentioned earlier, sodium stems from rocks and soils. Not only seas, but also rivers and lakes contain significant amounts of sodium. Concentrations however are much lower, depending on geological conditions and wastewater contamination.
Sodium is attributed water hazard class 2, in other words it is a risk when present in water. Sodium chloride however is not a risk and is attributed water hazard class 1.
Sodium is present in the human body in amounts of about 100 g. It is a dietary mineral, partially responsible for nerve functions. Blood serum contains 3.3 g/L sodium. It regulates extra cellular fluids, acid-base balance and membrane potential, partially together with potassium.
To remove sodium chloride from water, one may apply reverse osmosis, electro dialysis, distillation techniques or ion exchange. Reverse osmosis is most economical considering energy and money requirements.