The melting point and melting point of substance X are 321 and 765 degree respectively.In its molten state, X conducts electricity without decomposition.X probably has
A.ionic structure
B. metallic structure
C. simple molecular structure
Dcovalent network structure
Would you please tell me why the answer is B instrad of A and D?
ce chem 2000 q 17!Urgent!
2010-04-06 6:24 am
回答 (2)
2010-04-06 6:48 am
✔ 最佳答案
The ans is not A because if case of molten ionic substances, when conducting electricity, will undergo electrolysis which gives rise to a chemical change in form of decomposition.The ans is not D because besides graphite, covalent substances don't conduct electricity both in solid and molten state and since the given m.p. and b.p. are far lower than we expected for those of graphite, X is impossible to be graphite.
參考: Myself
2010-04-06 7:12 am
Melting point = 321 degree
Boiling point = 765 degree
The substance X has high melting point and boiling point, so the answer mustn't be C
The question states that in molten state. However, substances with giant covalent structure (covalent network structure) are so hard that it wasn't easily broken down as there is strong covalent bond between each atoms.Then, the covalent compound with giant covalent structure is insoluble in water.
Therefore, answer mustn't be D.
In fact, almost all substances with giant covalent structure can not conduct electricity, such as glass, diamond. However, graphite is an exceptional case. Only graphite can conduct electricity as there is delocalized electrons parallel to the hexagonal layer, thus it can conduct electricity without decomposition as the presence of delocalized e-. Nevertheless, it is insoluble in water and so it has no aq state.
Substances X conducts electricity without decomposition. For ionic compound with giant ionic structure, in molten state, the compound ionizes mobile ions in the water. Therefore, in molten state , it can conduct electricity as the presence of mobile ions. Taking NaCl as an example, NaCl will ionize Na+ and Cl- ions through ionization and solvation, which is the reason why NaCl(aq) can conduct electricity. However, ionization and solvation is the decomposition, that means for ionic compound, it must process decomposition (i,e. ionization and solvation) so as to conduct electricity as the decomposition produces mobile ions. In solid state of ionic compound, it cannot conduct electricity as the absence of delocalized electrons and mobile ions.
As a result, answer A is not correct
2010-04-05 23:13:53 補充：
So, the answer is B.
In fact, we can think of this question in this way:
1. Conduct electricity --> mean that the presence of delocalized electrons or mobile ions
2. Without decomposition --> point out that the substances can conduct electricity because of delocalized electrons only.
Boiling point = 765 degree
The substance X has high melting point and boiling point, so the answer mustn't be C
The question states that in molten state. However, substances with giant covalent structure (covalent network structure) are so hard that it wasn't easily broken down as there is strong covalent bond between each atoms.Then, the covalent compound with giant covalent structure is insoluble in water.
Therefore, answer mustn't be D.
In fact, almost all substances with giant covalent structure can not conduct electricity, such as glass, diamond. However, graphite is an exceptional case. Only graphite can conduct electricity as there is delocalized electrons parallel to the hexagonal layer, thus it can conduct electricity without decomposition as the presence of delocalized e-. Nevertheless, it is insoluble in water and so it has no aq state.
Substances X conducts electricity without decomposition. For ionic compound with giant ionic structure, in molten state, the compound ionizes mobile ions in the water. Therefore, in molten state , it can conduct electricity as the presence of mobile ions. Taking NaCl as an example, NaCl will ionize Na+ and Cl- ions through ionization and solvation, which is the reason why NaCl(aq) can conduct electricity. However, ionization and solvation is the decomposition, that means for ionic compound, it must process decomposition (i,e. ionization and solvation) so as to conduct electricity as the decomposition produces mobile ions. In solid state of ionic compound, it cannot conduct electricity as the absence of delocalized electrons and mobile ions.
As a result, answer A is not correct
2010-04-05 23:13:53 補充：
So, the answer is B.
In fact, we can think of this question in this way:
1. Conduct electricity --> mean that the presence of delocalized electrons or mobile ions
2. Without decomposition --> point out that the substances can conduct electricity because of delocalized electrons only.
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