Elemental silicon is oxidized by O 2 to give a compound which dissolves in molte

Question

Elemental silicon is oxidized by O2 to give a compound which dissolves in molten Na2CO3 . When this solution is treated with aqueous hydrochloric acid, a precipitate forms. What is the precipitate?

A. SiH4

B. SiCO3

C. SiO2

D. SiCl4

How do you know which mechanism is correct? The correct answer is C. Mechanism 1 gives C, but Mechanism 2 gives D. Please explain

Mechanism 1 (unbalanced):

1. Si+ O2 --> SiO2

2. SiO2 + Na2CO3 --> CO2 + Na2SiO3

3. Na2SiO3 + HCl (aq) --> NaCl + H2O (l) + SiO2

Mechanism 2 (unbalanced):

1. Si + O2 --> SiO2

2. SiO2 + Na2CO3 --> Na2O + Si(CO3)2

3. Si(CO3)2 + HCl (aq) --> SiCl4 + H2CO3

Explanation / Answer

Elemental silicon is oxidized by O2 to give a compound which dissolves in molten Na2CO3 . When this solution is treated with aqueous hydrochloric acid, SiO2 formed as a precipitate.

A:- C. SiO2

Mechanism 1 => Balanced

1. Si     +     O2      ----->      SiO2

2. SiO2    +     Na2CO3    ------>      CO2 + Na2SiO3

3. Na2SiO3   + 2 HCl (aq)    ----->     2 NaCl + H2O (l) + SiO2

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