[trishcurryx]

Hi all! I got this question today in chem.. Have NO idea how to go about it... Any ideas?

Describe how you would separate SiO₂, Al₂O₃ and MgO? Use equations to to explain your answer.

[formaldehyde23]

Hi there,

These are all oxides and you can separate them with melting point test.
You know that SiO2 is a network solid that is connected with directional covalent bonds. Also, MgO is an ionic solid with a high lattice energy: You have a 2+ cation and 2- anion, so the Coloumb's force is large. Finally, Al2O3 is an amphoteric oxide, so it won't have as high of a melting point compared to an ionic solid.
Therefore, the Al2O3 has the lowest melting point, followed by MgO, followed by SiO2.

[Dan]

These are all oxides and you can separate them with melting point test.

You can use a melting point test to distinguish between them, but not to separate them.

Also, your melting point order is incorrect.

Describe how you would separate SiO2, Al2O3 and MgO? Use equations to to explain your answer.

Start by looking up the chemistry of silica, alumina and magnesium oxide and how you can exploit their different reactivities to separate them. Also think about solubility.

You must demonstrate that you have put in some independent effort, this is a Forum Rule.

[trishcurryx]

Hi guys, thanks heaps!

I may have written the question wrong: Describe how you would separate a mixture of Al₂O₃ , MgO and SiO₂.

I've figured I could have the following equation to separate Magnesium:
MgO + H₂O  Mg²⁺ +2OH^-

However in this case, i'm then left with Magnesium ions... So how do I get separate the Mg ions from a solution?

[confusedstud]

I don't think magnesium oxide is able to react with water to form magnesium hydroxide though.

[Arkcon]

I don't think magnesium oxide is able to react with water to form magnesium hydroxide though.

Yes, it can: http://en.wikipedia.org/wiki/Magnesium_oxide