Sodium

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Sodium,  11Na
Sodium by Dnn87.jpg
General properties
Name, symbol Sodium, Na
Appearance White-silvery metal
Sodium in the periodic table
Li

Na

K
NeSodiumMg
Atomic number 11
Standard atomic weight (Ar) 22.98976928(2)
Group, block I; s-block
Period period 3
Electron configuration [Ne] 2s1
per shell
2, 8, 1
Physical properties
Silvery-white
Phase Solid
Melting point 370.944 K ​(97.794 °C, ​​208.029 °F)
Boiling point 1156.090 K ​(882.940 °C, ​​1621.292 °F)
Density near r.t. 0.968 g/cm3
when liquid, at  0.927 g/cm3
Critical point 2573 K, 35 MPa(extrapolated)
Heat of fusion 2.60 kJ/mol
Heat of 97.42 kJ/mol
Molar heat capacity 28.230 J/(mol·K)
 pressure
Atomic properties
Oxidation states +1, −1 ​(a strongly basic oxide)
Electronegativity Pauling scale: 0.93
energies 1st: 495.8 kJ/mol
2nd: 4562 kJ/mol
3rd: 6910.3 kJ/mol
Atomic radius empirical: 186 pm
Covalent radius 166±9 pm
Van der Waals radius 227 pm
Miscellanea
Crystal structure ​​body-centered cubic (bcc)
Speed of sound thin rod 3200 m/s (at 20 °C)
Thermal expansion 71 µm/(m·K) (at 25 °C)
Thermal conductivity 142 W/(m·K)
Electrical resistivity 47.7 Ω·m (at 20 °C)
Magnetic ordering paramagnetic
Young's modulus 10 GPa
Shear modulus 3.3 GPa
Bulk modulus 6.3 GPa
Mohs hardness 0.5
Brinell hardness 0.69 MPa
CAS Registry Number 7440-23-5
Discovery and first isolation Humphry Davy (1807)
· references

Sodium is an alkali metal with the symbol Na and the atomic number 11. A highly reactive metal that is less dense than water, it is quite cheap and depending on the location, easily available. It's not a chemical for beginners, but can have a plethora of uses in the intermediate and advanced chemists' labs.

Properties

Chemical

Sodium reacts with water in a well known and well loved reaction. The heat of the reaction causes the sodium to melt, forming spheres of metal that skirt over the surface of the water due to large amounts of hydrogen produced. The water turns alkaline with the formation of sodium hydroxide and the reaction often gets violent enough to ignite the hydrogen and in larger amounts, explode.

Sodium reacts quickly with air to form sodium oxides and hydroxides and so is often kept under mineral oil or an inert atmosphere, such as argon or even sulfur hexafluoride.
File:228592 orig-1-.jpg
The spectrum of sodium from a sodium lamp, using a CD as a diffraction grating.

Because of its reaction with water, sodium finds a common use in drying some solvents. However, a few solvents react with the metal, such as ethanol, to form sodium ethoxide.

Physical

Sodium is a very soft metal, easily cut with a knife. Its melting point is very low, at 88 degrees Celsius. It is quite ductile as well, taking a surprisingly low amount of force to extrude it (though it is somewhat difficult).

Availability

While the bulk 'price' of sodium is seen to be low, buying small quantities of the metal is usually quite an expensive process. The difficulty and legality of shipping a reactive metal often significantly adds to its price and many online companies will refuse to ship this overseas.

GalliumSource sells sodium by the kilo.

Australia

In some countries, such as Australia, availability is further limited by laws designed to prevent it being used in the manufacture of illicit drugs. Laws are in place that state one needs to sign an EUD (End user declaration) on buying this chemical which is a confusing, poorly enforced and seemingly outdated law for the internet age. In much the way many 'restricted' chemicals in Australia are treated, it is unsure whether owning sodium metal without an EUD would be illegal.

If anyone from Australia has run into issues, or even managed to get an online supplier to sign an EUD before, a comment here would be much appreciated.

Preparation

There are many methods known for producing sodium, many of which seem easy theoretically but pose their own practical challenges. Producing sodium at home on a large scale is generally not feasible due to the conditions under which the reactions must take place, but is a great project and achievement for the experienced amateur.

Electrolysis

Molten sodium hydroxide (cheaply available) is electrolyzed in a stainless steel or nickel container, in a process known as Castner process.

Anode:

2OH → ½O2 + H2O + 2e

Catode:

2Na+ + 2e → 2Na

Overall, the reaction is:

4NaOH → 4Na + H2 + H2O + O2

This process has the downsides of using molten NaOH, which is incredibly corrosive. The vapors given off by the electrolysis process aerosolize small amounts of sodium hydroxide, forming a highly dangerous fog. Passing the evacuated gases through a scrubber is a must, as the fog is highly corrosive to the skin, eyes (especially eyes), mucous membranes.

Another process, known as Downs process, involves the electrolysis of a molten mixture of 65/45 NaCl/CaCl2, at 660 degrees Celsius. A significant challange involves the prevention of hot molten sodium from catching fire at these temperatures (such as an inert atmosphere), especially on contact with hot chlorine or air.

Reduction with magnesium

Metallic sodium can be obtained by reducing sodium hydroxide with magnesium metal, in a thermite like reaction. Because hot sodium will easily catch fire in open air, it's best to do it in an inert container.

Projects

  • Make NaK (sodium potassium alloy) by fusing the two metals together. NaK containing 40% to 90% potassium by weight is liquid at room temperature. The eutectic mixture consists of 77% potassium and 23% sodium, is liquid from −12.6 to 785 °C, and has a density of 866 kg/m3 at 21 °C and 855 kg/m3 at 100 °C, making it less dense than water.[1] It is highly reactive with water and is stored under dry nitrogen (or, even better, dry argon) for safety reasons
  • Dry aprotic solvents
  • Make sodium ethoxide

Handling

Safety

While the sodium ion is non-toxic, the metal itself poses more of a physical danger due to its high reactivity. Sodium has a reputation to explode in water, throwing out fire and corrosive sodium hydroxide solution.

Always handle sodium with tongs or tweezers. Counter intuitive as it may seem, it is better not to use gloves directly. If you wear gloves it is very difficult to tell if they are dry, and will risk burning your hand off. And if you wear gloves when it catches fire, the burns will be more severe, as the gloves will melt and stick on the skin.

Using tongs, tweezers, pliers or stabbing the soft metal with a scalpel is the best way to pick sodium up.

Storage

Sodium metal should be stored in closed containers, under mineral oil, or under inert atmosphere, such as argon or sulfur hexafluoride. If stored under oil, it will slowly oxidize, though this depends on the container.

Disposal

Disposal of sodium should be done in a safe area by reacting the metal with anhydrous isopropanol (you can burn or throw the metal in water, but that's significantly more dangerous). Sodium hydroxide can be neutralized with any acid (though acetic acid or citric acid are cheaper).

References

  • Tdep - Details off the top of my head. Feel free to argue points with me.

Relevant Sciencemadness threads