Silicon

Chemical reactions




Reaction of silicon with acids


Silicon does not react with most acids, under normal conditions. It is dissolved by hydrofluoric acid, HF, most likely due to the complex formation of [SiF6]2−, as the driving force.

Si(s) + 6 HF(aq) [SiF6]2−(aq) + 2H+(aq) + 2 H2(g)


Reaction of silicon with air


Silicon is passivated by a thin layer of SiO2 on the surface, and does not otherwise react with air under normal conditions.

If heated above 900 °C, silicon reacts with the oxygen, O2, forming SiO2:

Si(s) + O2(g) SiO2(s)


If heated above 1400 °C, silicon reacts with the nitrogen, N2, forming the silicon nitrides SiN and Si3N4:

2 Si(s) + N2(g) 2 SiN(s)
3 Si(s) + 2 N2(g) Si3N4(s)


Reaction of silicon with bases


Silicon reacts with hot alkali solutions, forming silicate ions, SiO32− [5]:

Si(s) + 2 OH(aq) SiO32−(aq) + 2 H2(g)


Reaction of silicon with halogens


Silicon reacts halogens, forming the corresponding Si(IV) halides.

Si(s) + 2 F2(g) SiF4(g) [5]
Si(s) + 2 Cl2(g) SiCl4(l) [5]
Si(s) + 2 Br2(g) SiBr4(l)
Si(s) + 2 I2(g) SiI4(s)


Reaction of silicon with water


Silicon does not react with water, even as steam, under normal conditions.


Quantitative analysis


Method 4500-Si G 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 = 0.05 mg/L