Potassium

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Other names/abbreviations:

K Kalium

Element no:	19
Element group:	1 (IUPAC) I A (American labelling) I A (European labelling) Alkali metals
Element type:	Metals
CAS-Number:	7440-09-7
EINECS-Number:	231-119-8

Quantitative analysis

Method 3500-K C Inductively Coupled Plasma Method [1]. A portion of the sample is digested in a combination of acids. The digest is aspirated into an 8,000 K argon plasma where resulting light emission is quantified for 30 elements simultaneously.

Method limit of detection in water = 1.0 mg/L
Method limit of detection in soil = 100.0 mg/kg

Safety

Symbol: F, C
R-phrases: 14/15-34
S-phrases: 5-8-43-45

Physical properties

Appearance
	Physical state @ 20°C:	Solid [4]
	Color:	Silvery [4]

Bulk properties
	Molecular weight (g/mol):	39.0983(1) [2]
	Melting point (°C):	63.7 [2]
	Boiling point (°C):	759 [2]
	Density (g/cm3):	0.856 [2]
	Molar volume (cm3):	45.50 (20 °C) [3]
	Elastic properties: Rigidity modulus (GPa): Bulk modulus (GPa):	1.30 [3] 3.1 [3]
	Hardnesses: Mineral hardness:	0.5 [3]

Thermodynamic properties
	ΔfH°gas (kJ/mol):	89.0 (monoatomic) [5] 123.7 (K2) [5]
	ΔfH°solid (kJ/mol):	0.0 (monoatomic) [5]
	ΔH°fusion (kJ/mol):	2.32 [5]
	ΔH°vaporization (kJ/mol):	79 [2]
	S°gas (J/K·mol):	160.3 (monoatomic) [5] 249.7 (K2) [5]
	S°solid (J/K·mol):	64.7 (monoatomic) [5]
	ΔfG°gas (kJ/mol):	60.5 (monoatomic) [5] 87.5 (K2) [5]
	Cp (gas) (J/K·mol):	20.8 (25 °C) [5] 37.9 (K2, 25 °C) [5]
	Cp (solid) (J/K·mol):	29.600 (25 °C) [5]

Crystal structure
	Crystal type:	Body centered cubic [3]

Electronic properties
	Electron configuration:	1s2-2s2-2p6-3s2-3p6-4s1
	Atomic radius (Å):	2.31 [6]
	Ionic radius (Å):	1.38 [2]
	Electron affinity [M-M-] (kJ/mol):	46.36 [2]

Conductivity
	e°(V):	K(I)/K: -2.925 [2]
	Electrical resisitvity (μΩ·cm):	6.80 (20 °C) [3] 7.47 (25 °C) [3]
	Thermal (W/m·K):	102.4 (27 °C) [5]

Misc.
	Vapour pressure (Pa):	13300 (171 °C) [4]

Occurrence, isolation & synthesis

Isolation
Potassium is produced by the reaction of molten Na and KCl [6]:

Na (l) + KCl (l) K (l) + NaCl (l)

The sodium is fed at the bottom of a column and the molten potassium comes out at the top.

References

1: Standard Methods for the Analysis of Water and Wastewater, APHA, 1992, 18th edition

2: Greenwood,N.N., Earnshaw,A. Chemistry of the elements
2nd edition (1997) Edited by Greenwood,N.N., Earnshaw,A. pp. 1-1340, Butterworth-Heinemann. Oxford. Great Britain

3: Buch,A. Pure Metals Properties. A Scientific-Technical Handbook
1st edition (1999) Edited by Buch,A. pp. 1-306, ASM International and Freund Publishing House Ltd. Ohio. USA

4: Merck. ChemDAT The Merck Chemical Database Ver. 1.1.5

5: CRC Handbook of Chemistry and Physics
75th edition (1994) Edited by Lide,D.R. , CRC Press Inc. Boca Raton, USA

6: General chemistry
7th edition (1984) Edited by Holtzclaw, Jr.,H.F., Robinson,W.R. & Nebergall,W.H. pp. 1-932. D.C. Heath and Company. Lexington

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© Michael Pilgaard
Created: October 2, 2008
Last update: October 9, 2008