why cant Al2O3 dissolve? Watch

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presebjenada
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Why cant Al2O3 dissolve?
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T.r.i.n.i.t.y
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(Original post by presebjenada)
Why cant Al2O3 dissolve?
im stuck in that too. i think the reason is simply, that because the electronegativity differece between Al and O is smaller than that in Mg and O and Na and O. Al polarises the choliride ion, introducing covalent character into the bond. The giant lattice and the covalency on Al2o3 makes it insoluble in water..thats my opinion.. lolz
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Stunt-101
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Al203 doesnt dissolve is part of Q5 (the essay) of trends june 02, this is part of the Period 3 section and its cos aluminium oxide has a giant ionic lattice structure with covalent bonding - so it has intermediate bonding making it insoluble - unable to react with water. Its got intermediate properties - if u got the cambridge t/book see p87
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ResidentEvil
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well, it actually has ionic bonding with covalent character, thereby making it insoluble. SiO2 is also insoluble because it is in giant molecular structure with covalent and van der waal bonding.
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Stunt-101
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(Original post by ResidentEvil)
well, it actually has ionic bonding with covalent character, thereby making it insoluble. SiO2 is also insoluble because it is in giant molecular structure with covalent and van der waal bonding.
so why doesntit dissolve cos i just copied what it sed out the tbook?
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ResidentEvil
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(Original post by Stunt-101)
so why doesntit dissolve cos i just copied what it sed out the tbook?
I think its wholly because of the intermediate bondings, but its not detailed in the syllabus so i doubt they can ask u it. Even if they do, they'll provide u with various clues prior to the question.
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mongoose
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(Original post by ResidentEvil)
I think its wholly because of the intermediate bondings, but its not detailed in the syllabus so i doubt they can ask u it. Even if they do, they'll provide u with various clues prior to the question.
Yeah, i don't think they'd require any answer more complex than within the scope of the strong bonding to explain why it's insoluble. Otherwise, you'd need to draw an enthalpy cycle to explain why it was insoluble. Solution enthalpy is the sum of the lattice enthalpy and the hydration/solvation enthalpy - ie the solid lattice needs to be seperated into ions before it can dissolve, once the lattice has been seperated the ions are then surrounded and stabilised by water/solvent molecules. For something to dissolve the energy holding the lattice together needs to be comparable to the combined energies of the solvent molecules surrounding the ion (ie the hydration/solvation enthalpy) to compensate for the energy change. If this energy requirement isn't met, the the substance either won't dissolve, or be only sparingly soluble. So, the larger the solution enthalpy, the more soluble. But i can't imagine them asking this sort of question on a paper... that is, unless your'e doing solids/liquids/gases (OCR).
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