# I can't choose the set of 3 chemicals with each of which Si will react (out of 5 possible sets)

This is one of the questions used in the Russian State Chemistry Exam. One needs to select the set of chemicals in the second column such that each of them would react with the element or chemical in the the first column.

I mean, it should react with each element in the set in order for that set to be suitable.

It seems to me that $\ce{Si}$ has no suitable set among those five.

It does not react with $\ce{Na2CO3}$ (that excludes set 1), with $\ce{HCl}$ (set 2), with$\ce{MgO}$ (set 3), with $\ce{H2SO4}$ (set 4) and with$\ce{Al(OH)3}$ (set 5).

I used Chemguide and a Russian school curriculum-based website to refresh my memory of $\ce{Si}$ activity.

Am I wrong in regard of any of the five chemicals? Maybe it will react with $\ce{MgO}$, for instance?

$\ce{Si}$ does in fact react with $\ce{HF}$ and $\ce{NaOH}$. The reactions would be:

$$\ce{Si + 4HF -> SiF4 + 2H2}$$

$$\ce{Si + 4NaOH -> Na4SiO4 + 2H2}$$

$$\ce{Si + 2MgO -> SiO2 + 2Mg}$$

You can conclude these, since $\ce{SiO2}$ is quite stable, and also reacts with $\ce{HF}$ and $\ce{NaOH}$ (You may have heard that $\ce{HF}$ dissolves glass), so definitely $\ce{Si}$ will react way better than $\ce{SiO2}$.

• Yes, but it does not react with MgO, and that excludes set 3. – CowperKettle Apr 23 '17 at 12:17
• My bad, I forgot to mention its reaction with MgO, I'll add it now. – Pritt Balagopal Apr 23 '17 at 12:18
• I have added the reaction, the one with $\ce{MgO}$ is also called the Pidgeon Process. More about it: en.m.wikipedia.org/wiki/Pidgeon_process – Pritt Balagopal Apr 23 '17 at 12:21
• Thank you! I knew that it reacts with Mg to produce MgO so I assumed the reverse reaction was unlikely. – CowperKettle Apr 23 '17 at 12:23
• – Nilay Ghosh Apr 23 '17 at 15:03

Maybe it also react with the chemicals from set 2.

1. $\ce{HCl}$

$$\ce{Si + 3HCl ->[\Delta] SiHCl3 + H2}$$

Silicon react with hydrogen chloride to produce trichlorosilane and hydrogen. This reaction takes place at a temperature near 350°C. In this reaction, the catalyst is can be copper.(chemiday 1)

1. $\ce{O2}$

$$\ce{Si + O2 ->[\Delta] SiO2}$$

Silicon react with oxygen to produce silicon dioxide. This reaction takes place at a temperature of 1200-1300°C.(chemiday 2)

1. $\ce{Cl2}$

$$\ce{Si + 2Cl2 ->[\Delta] SiCl4}$$

Silicon react with chlorine to produce silicon(IV) chloride. This reaction takes place at a temperature of 340-420°C, in a flow argon.(chemiday 3)

Maybe you doubted the reaction between silicon and hydrogen chloride.

• The Russian textbook I was referring to confidently stated that it only reacts with hydrofluoric acid (HF). – CowperKettle Apr 23 '17 at 15:00
• @CopperKettle en.m.wikipedia.org/wiki/Trichlorosilane – Nilay Ghosh Apr 23 '17 at 15:04
• @CopperKettle silicon reacts with hydrogen only in presence of silicon tetrachloride to form trichlorosilane. So I excluded it. – Nilay Ghosh Apr 23 '17 at 15:13