Difference between revisions of "Potassium"

From Sciencemadness Wiki
Jump to: navigation, search
(Added infobox and image)
Line 1: Line 1:
 +
{{Infobox element
 +
<!-- top -->
 +
|image name=Potassium metal by NileRed.png
 +
|image alt=
 +
|image size=300
 +
|image name comment=Potassium metal in mineral oil, after being cleaned.
 +
|image name 2=
 +
|image alt 2=
 +
|image size 2=
 +
|image name 2 comment=
 +
<!-- General properties -->
 +
|name=Potassium
 +
|symbol=K
 +
|pronounce=
 +
|pronounce ref=
 +
|pronounce comment=
 +
|pronounce 2=
 +
|alt name=
 +
|alt names=
 +
|allotropes=
 +
|appearance=Silvery-white metal
 +
<!-- Periodic table -->
 +
|above=[[Sodium|Na]]
 +
|below=[[Rubidium|Rb]]
 +
|left=[[Argon|Ar]]
 +
|right=[[Calcium|Ca]]
 +
|number=19
 +
|atomic mass=39.0983(1)
 +
|atomic mass 2=
 +
|atomic mass ref=
 +
|atomic mass comment=
 +
|series=Alkali metals
 +
|series ref=
 +
|series comment=
 +
|series color=
 +
|group=1
 +
|group ref=
 +
|group comment=I
 +
|period=4
 +
|period ref=
 +
|period comment=
 +
|block=s
 +
|block ref=
 +
|block comment=
 +
|electron configuration= [Ar] 2s<sup>1</sup>
 +
|electron configuration ref=
 +
|electron configuration comment=
 +
|electrons per shell=2, 8, 8, 1
 +
|electrons per shell ref=
 +
|electrons per shell comment=
 +
<!-- Physical properties -->
 +
|physical properties comment=
 +
|color=Silvery-white
 +
|phase=Solid
 +
|phase ref=
 +
|phase comment=
 +
|melting point K=336.7
 +
|melting point C=63.5
 +
|melting point F=​146.3
 +
|melting point ref=
 +
|melting point comment=
 +
|boiling point K=1032
 +
|boiling point C=759
 +
|boiling point F=​1398
 +
|boiling point ref=
 +
|boiling point comment=
 +
|sublimation point K=
 +
|sublimation point C=
 +
|sublimation point F=
 +
|sublimation point ref=
 +
|sublimation point comment=
 +
|density gplstp=
 +
|density gplstp ref=
 +
|density gplstp comment=
 +
|density gpcm3nrt=0.862
 +
|density gpcm3nrt ref=
 +
|density gpcm3nrt comment=
 +
|density gpcm3nrt 2=
 +
|density gpcm3nrt 2 ref=
 +
|density gpcm3nrt 2 comment=
 +
|density gpcm3nrt 3=
 +
|density gpcm3nrt 3 ref=
 +
|density gpcm3nrt 3 comment=
 +
|density gpcm3mp=0.828
 +
|density gpcm3mp ref=
 +
|density gpcm3mp comment=
 +
|density gpcm3bp=
 +
|density gpcm3bp ref=
 +
|density gpcm3bp comment=
 +
|molar volume=
 +
|molar volume unit =
 +
|molar volume ref=
 +
|molar volume comment=
 +
|triple point K=
 +
|triple point kPa=
 +
|triple point ref=
 +
|triple point comment=
 +
|triple point K 2=
 +
|triple point kPa 2=
 +
|triple point 2 ref=
 +
|triple point 2 comment=
 +
|critical point K=2223
 +
|critical point MPa=16
 +
|critical point ref=
 +
|critical point comment=
 +
|heat fusion=2.33
 +
|heat fusion ref=
 +
|heat fusion comment=
 +
|heat fusion 2=
 +
|heat fusion 2 ref=
 +
|heat fusion 2 comment=
 +
|heat vaporization=76.9
 +
|heat vaporization ref=
 +
|heat vaporization comment=
 +
|heat capacity=29.6
 +
|heat capacity ref=
 +
|heat capacity comment=
 +
|heat capacity 2=
 +
|heat capacity 2 ref=
 +
|heat capacity 2 comment=
 +
|vapor pressure 1=
 +
|vapor pressure 10=
 +
|vapor pressure 100=
 +
|vapor pressure 1 k=
 +
|vapor pressure 10 k=
 +
|vapor pressure 100 k=
 +
|vapor pressure ref=
 +
|vapor pressure comment=
 +
|vapor pressure 1 2=
 +
|vapor pressure 10 2=
 +
|vapor pressure 100 2=
 +
|vapor pressure 1 k 2=
 +
|vapor pressure 10 k 2=
 +
|vapor pressure 100 k 2=
 +
|vapor pressure 2 ref=
 +
|vapor pressure 2 comment=
 +
<!-- Atomic properties -->
 +
|atomic properties comment=
 +
|oxidation states='''+1''', −1 ​(a strongly basic oxide)
 +
|oxidation states ref=
 +
|oxidation states comment=
 +
|electronegativity=0.82
 +
|electronegativity ref=
 +
|electronegativity comment=
 +
|ionization energy 1=418.8
 +
|ionization energy 1 ref=
 +
|ionization energy 1 comment=
 +
|ionization energy 2=3052
 +
|ionization energy 2 ref=
 +
|ionization energy 2 comment=
 +
|ionization energy 3=4420
 +
|ionization energy 3 ref=
 +
|ionization energy 3 comment=
 +
|number of ionization energies=10
 +
|ionization energy ref=
 +
|ionization energy comment=
 +
|atomic radius=227
 +
|atomic radius ref=
 +
|atomic radius comment=
 +
|atomic radius calculated=
 +
|atomic radius calculated ref=
 +
|atomic radius calculated comment=
 +
|covalent radius=203±12
 +
|covalent radius ref=
 +
|covalent radius comment=
 +
|Van der Waals radius=275
 +
|Van der Waals radius ref=
 +
|Van der Waals radius comment=
 +
<!-- Miscellanea -->
 +
|crystal structure=
 +
|crystal structure prefix=
 +
|crystal structure ref=
 +
|crystal structure comment= ​body-centered cubic (bcc)
 +
|crystal structure 2=
 +
|crystal structure 2 prefix=
 +
|crystal structure 2 ref=
 +
|crystal structure 2 comment=
 +
|speed of sound=
 +
|speed of sound ref=
 +
|speed of sound comment=
 +
|speed of sound rod at 20=2000
 +
|speed of sound rod at 20 ref=
 +
|speed of sound rod at 20 comment=
 +
|speed of sound rod at r.t.=
 +
|speed of sound rod at r.t. ref=
 +
|speed of sound rod at r.t. comment=
 +
|thermal expansion=
 +
|thermal expansion ref=
 +
|thermal expansion comment=
 +
|thermal expansion at 25=83.3
 +
|thermal expansion at 25 ref=
 +
|thermal expansion at 25 comment=
 +
|thermal conductivity=102.5
 +
|thermal conductivity ref=
 +
|thermal conductivity comment=
 +
|thermal conductivity 2=
 +
|thermal conductivity 2 ref=
 +
|thermal conductivity 2 comment=
 +
|thermal diffusivity=
 +
|thermal diffusivity ref=
 +
|thermal diffusivity comment=
 +
|electrical resistivity=
 +
|electrical resistivity unit prefix=
 +
|electrical resistivity ref=
 +
|electrical resistivity comment=
 +
|electrical resistivity at 0=
 +
|electrical resistivity at 0 ref=
 +
|electrical resistivity at 0 comment=
 +
|electrical resistivity at 20=72
 +
|electrical resistivity at 20 ref=
 +
|electrical resistivity at 20 comment=
 +
|band gap=
 +
|band gap ref=
 +
|band gap comment=
 +
|Curie point K=
 +
|Curie point ref=
 +
|Curie point comment=
 +
|magnetic ordering=paramagnetic
 +
|magnetic ordering ref=
 +
|magnetic ordering comment=
 +
|tensile strength=
 +
|tensile strength ref=
 +
|tensile strength comment=
 +
|Young's modulus=3.53
 +
|Young's modulus ref=
 +
|Young's modulus comment=
 +
|Shear modulus=1.3
 +
|Shear modulus ref=
 +
|Shear modulus comment=
 +
|Bulk modulus=3.1
 +
|Bulk modulus ref=
 +
|Bulk modulus comment=
 +
|Poisson ratio=
 +
|Poisson ratio ref=
 +
|Poisson ratio comment=
 +
|Mohs hardness=0.4
 +
|Mohs hardness ref=
 +
|Mohs hardness comment=
 +
|Mohs hardness 2=
 +
|Mohs hardness 2 ref=
 +
|Mohs hardness 2 comment=
 +
|Vickers hardness=
 +
|Vickers hardness ref=
 +
|Vickers hardness comment=
 +
|Brinell hardness=0.363
 +
|Brinell hardness ref=
 +
|Brinell hardness comment=
 +
|CAS number=7440-09-7
 +
|CAS number ref=
 +
|CAS number comment=
 +
<!-- History -->
 +
|naming=
 +
|predicted by=
 +
|prediction date ref=
 +
|prediction date=
 +
|discovered by=
 +
|discovery date ref=
 +
|discovery date=
 +
|first isolation by=
 +
|first isolation date ref=
 +
|first isolation date=
 +
|discovery and first isolation by=Humphry Davy (1807)
 +
|named by=
 +
|named date ref=
 +
|named date=
 +
|history comment label=
 +
|history comment=
 +
<!-- Isotopes -->
 +
|isotopes=
 +
|isotopes comment=
 +
|engvar=
 +
}}
 
'''Potassium''' is a silvery white alkali metal which has limited applications in the home lab due to its highly reactive nature.  
 
'''Potassium''' is a silvery white alkali metal which has limited applications in the home lab due to its highly reactive nature.  
  

Revision as of 19:07, 18 February 2016

Potassium,  19K
Potassium metal by NileRed.png
Potassium metal in mineral oil, after being cleaned.
General properties
Name, symbol Potassium, K
Appearance Silvery-white metal
Potassium in the periodic table
Na
↑
K
↓
Rb
Ar ← Potassium → Ca
Atomic number 19
Standard atomic weight (Ar) 39.0983(1)
Group, block I; s-block
Period period 4
Electron configuration [Ar] 2s1
per shell
 2, 8, 8, 1
Physical properties
Silvery-white
Phase Solid
Melting point 336.7 K ​(63.5 °C, ​​146.3 °F)
Boiling point 1032 K ​(759 °C, ​​1398 °F)
Density near r.t. 0.862 g/cm3
when liquid, at  0.828 g/cm3
Critical point 2223 K, 16 MPa
Heat of fusion 2.33 kJ/mol
Heat of 76.9 kJ/mol
Molar heat capacity 29.6 J/(mol·K)
Atomic properties
Oxidation states +1, −1 ​(a strongly basic oxide)
Electronegativity Pauling scale: 0.82
energies 1st: 418.8 kJ/mol
2nd: 3052 kJ/mol
3rd: 4420 kJ/mol
(more)
Atomic radius empirical: 227 pm
Covalent radius 203±12 pm
Van der Waals radius 275 pm
Miscellanea
Crystal structure ​​body-centered cubic (bcc)
Speed of sound thin rod 2000 m/s (at 20 °C)
Thermal expansion 83.3 µm/(m·K) (at 25 °C)
Thermal conductivity 102.5 W/(m·K)
Electrical resistivity 72 Ω·m (at 20 °C)
Magnetic ordering paramagnetic
Young's modulus 3.53 GPa
Shear modulus 1.3 GPa
Bulk modulus 3.1 GPa
Mohs hardness 0.4
Brinell hardness 0.363 MPa
CAS Registry Number 7440-09-7
Discovery and first isolation Humphry Davy (1807)
· references

Potassium is a silvery white alkali metal which has limited applications in the home lab due to its highly reactive nature.

Properties

Chemical

Potassium is highly reactive with water, forming hydrogen and potassium hydroxide upon contact. The reaction is so exothermic, the hydrogen is instantly ignited, forming a burning sphere of potassium. It can be alloyed with sodium to form NaK, which is liquid at room temperature and is sometimes used to dry solvents.

Physical

Potassium is a silvery white metal which will tarnish quickly in air. It melts at 63.5°C and can easily be cut with a butter knife. Potassium has a low boiling point of 759°C and is therefore often purified industrially by distillation, however this is not viable for the amateur and is extremely dangerous due to high risk of explosion.

Availability

Potassium metal is generally not available from lab suppliers, but stores which cater to element collectors such as GalliumSource and Metallium sell potassium. Potassium bought this way is very expensive and can be up to $10 per gram.

Preparation

Potassium metal can be prepared in a well equipped home lab without too much difficulty. Potassium hydroxide and magnesium are combined in an anhydrous, inert, fully saturated solvent and the mixture is brought to reflux. A good choice of solvent is tetralin or Shellsol D70, however these are difficult to find and mineral oil or kerosene may be used, though success with these alternatives has yet to be substantially demonstrated. The reaction may not reflux if these more accessible solvents are used and the temperature must just be maintained at 200°C instead. A catalyst of a tertiary alcohol, such as t-butanol or t-amyl alcohol, is then added and, over the course of several hours, spheres of potassium will slowly form. The reaction mixture can then be dumped out into toluene and the spheres of potassium taken out and ampouled for storage. It is important to note that without very, very pure reagents, success is unlikely. Even mildly tarnished magnesium turnings/powder may not react well enough to produce potassium.

Projects

Handling

Safety

Potassium is highly reactive and may ignite in air or on contact with organic materials (like paper) under the right circumstances. Potassium compounds have little toxicity taken orally, but injecting potassium ions will lead to rapid cardiac arrest and death. People with cardiac problems should limit the consumption of potassium compounds.

NEVER HANDLE POTASSIUM WITH GLOVES! It's easy to tell if your hands are wet, but it is not easy to tell if gloves are wet. If you handle potassium with thick oven mitts and the potassium ignites, it will burn through the gloves in less than two seconds. Handle potassium with your bare hands, counterintuitive as it may seem. A better method, however, is to poke the potassium with a screwdriver or other metal stick, due to the extreme sectile properties of the metal. (If you use a non-metal stick, the potassium will react with it, unless it's glass.)

Storage

Potassium metal is highly reactive with water and care must be taken to prevent contact as this will result in a fire. Potassium must be stored in a flame sealed ampoule if it is to be stored for more than a month, due to a black layer of oxides and superoxides which will build up and may become a shock sensitive explosive. If it is to be stored for less than a month, it can be stored in a tightly closed vial under mineral oil.

Disposal

While it is easy to just chuck a piece in water, the safest method of destruction is the addition of anhydrous isopropyl alcohol to any pieces. This forms potassium isopropoxide, which can be disposed of safely by neutralizing it with a soluble carbonate solution.

Throwing large pieces of potassium in water can cause an explosion and may send hot pieces of potassium metal flying.

References

Relevant Sciencemadness threads

Retrieved from "https://www.sciencemadness.org/smwiki/index.php?title=Potassium&oldid=3928"