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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: vanderwaals on February 19, 2017, 08:58:06 PM

Title: Precipitate with Si
Post by: vanderwaals on February 19, 2017, 08:58:06 PM
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

The answer is (C). I'm just very confused about what happens here. I thought that after elemental silicon is oxidized (the first step), SiO2 would be produced...but I have no idea if that's correct. I don't know what the reaction with HCl has to do with anything either. Could someone guide me through what happens after each reaction? Thanks in advance!
Title: Re: Precipitate with Si
Post by: thetada on February 19, 2017, 09:12:22 PM
What effect do you think the hydrochloric acid might have on the sodium carbonate?
Title: Re: Precipitate with Si
Post by: vanderwaals on February 19, 2017, 11:22:59 PM
Well it reacts to form water and carbon dioxide...but I'm not sure how this is related to the precipitate
Title: Re: Precipitate with Si
Post by: AWK on February 20, 2017, 01:51:41 AM
Quote
to give a compound
which dissolves in molten Na2CO3
This is chemical reaction.
See wikipedia: sodium silicate.
Title: Re: Precipitate with Si
Post by: thetada on February 20, 2017, 04:59:30 PM
Quote from: vanderwaals on February 19, 2017, 11:22:59 PM
Well it reacts to form water and carbon dioxide...but I'm not sure how this is related to the precipitate

Turns out nothing but it doesn't hurt to consider all possibilities. The question is very misleadingly phrased, it's not dissolving to make a solution, it's reacting to make a new species.