In this tutorial, you will learn about the reaction between sodium and water, what causes it and how it works.
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Sodium explodes in Water
When you wet a piece of sodium metal, it gets hot and fizzes; sometimes the reaction can be extreme enough to produce flames and explosions. However, when sodium chloride comes into contact with water, it simply dissolves; and when chlorine is dropped into water, it acts as a disinfectant, killing bacteria and microorganisms. So what about sodium itself causes such a violent reaction? The answer has to do with the quantum interactions between the metal and the water molecules.
Stability of Sodium and Water
It can be a little easier to understand this reaction when you think of sodium compared to a noble gas; it is similar to neon, which has ten protons and ten electrons. Noble gases are known for their stability due to their full atomic orbitals, not needing to gain or lose electrons; neon has its 1s, 2s, and 2p orbitals are full. This stability is ruined when you detour from noble gases, such as with sodium. This element has 11 protons, and the ‘extra’ electron is held on very loosely with the next atomic orbital. This is why sodium so readily gives up an electron in compounds such as sodium chloride, which forms a stable bond.
On the other hand, water may look like a stable molecule but is a highly polar molecule. Because of its bent shape, there is one side of the oxygen has a preferred negative charge (the side with the lone pairs) while the other has a preferred positive charge (the side with the two hydrogens). When there is a lot of liquid water together, the molecules position themselves so that the negative ends ‘neutralize’ the positive ends and the electric potential energy is minimized. Some of the water molecules, one in millions, will dissociate into their respective ions – the proton (H+) and hydroxyl (OH–) ions.
Mixing Sodium and Water
When you mix sodium with polar water, protons, and hydroxyl ions, what happens? The loosely held electron from the sodium will want to react with the single proton it can find. The electrons from sodium combine with hydrogen ions which happens as more neutral water molecules dissociate to provide free protons; this takes about 13.6 eV of energy. The neutral hydrogen atoms are moving towards an energetically favorable state, the neutral diatomic gas H2 , which comes with 13.6 eV of energy pushed into the system.
Sodium Metal and Water Reaction Equation
In this exothermic reaction, solid sodium mixes with water to form a colorless basic solution made of strong alkalic sodium hydroxide and hydrogen gas. During the interaction, the sodium can heat up so much that it burns an orange flame. Below is the reaction:
2Na(s) + 2H2O → 2NaOH(aq) + H2(g)
Now you have energy in the form of heat and hydrogen gas which wants to escape into the atmosphere which contains oxygen gas (O2). This causes hydrogen/oxygen combustion! These two in the presence of heat energy produce water vapor and more energy, explaining the intense and explosive reaction. This reaction continues until the sodium is fully dissolved into its ionized and soluble form of Na+.
Can Sodium Metal be dangerous to health?
Although we just learned sodium metal can be explosive when exposed to water, sodium is actually needed in the body, as is it a dietary mineral that is needed for nerve functions. (Check out our tutorial on neurotransmitters for more). Blood serum is used in the regulation of internal acid-base balance, membrane potential, and extracellular fluids. We ingest sodium in its neutralized form of sodium chloride, or table salt. Due to the extra electron on sodium interacting with the chlorine, it does not interact with the protons in water.
So, sodium won’t interact with water and explode in your body; however, sodium intake does have to be monitored due to its health effects. Ingesting too much salt can cause a spike in blood pressure, hyperosmolarity, increased risk of infections, arteriosclerosis, and more. On the other hand, not ingesting enough sodium in your diet can also cause adverse effects, such as dehydration, muscle abnormalities, convulsions, and more. An intake of about 300 mg of salt daily is an approximate healthy value.