Which row describes silicon dioxide?
| Electrical conductivity in liquid state | Solubility in water | |
|---|---|---|
| A | non-conductor | insoluble |
| B | non-conductor | soluble |
| C | conductor | insoluble |
| D | conductor | soluble |
Correct Answer: \( \boxed{\mathrm{A}} \)
Silicon dioxide has a giant covalent structure.
Therefore, the correct answer is (A).
In which substance are covalent bonds broken as it melts?
Correct Answer: \( \boxed{\mathrm{A}} \)
Silicon(IV) oxide has a giant covalent structure. Melting requires breaking some of the strong covalent bonds in the three-dimensional network.
Ice, iodine and ethanol are simple molecular substances. When they melt, only the intermolecular forces (hydrogen bonding or van der Waals’ forces) are overcome, while the covalent bonds within the molecules remain intact.
Therefore, the correct answer is (A).
Substance W has the physical properties shown.
| m.p. / \(^{\circ}\mathrm{C}\) | b.p. / \(^{\circ}\mathrm{C}\) | Electrical conductivity | ||
|---|---|---|---|---|
| Of solid | Of liquid | In water | ||
| 2072 | 2980 | Poor | Good | Insoluble |
What is substance W?
Correct Answer: \( \boxed{\mathrm{A}} \)
The substance has a very high melting point and boiling point, indicating a giant lattice structure.
It conducts electricity when molten but not when solid, showing that mobile ions are present only in the liquid state. It is also insoluble in water.
These properties are characteristic of aluminium oxide, a giant ionic compound with very strong electrostatic attractions.
Iron conducts electricity in both the solid and liquid states, silicon dioxide does not conduct in either state, and sodium fluoride is soluble in water.
Therefore, the correct answer is (A).
