Which particles conduct electricity in molten lead (II) bromide and lead metal? Explain melting point differences for ionic and covalent chlorides.

Here are the answers to your questions:

5. Which particles conduct electricity in:

a) Molten lead (II) bromide
✅ Correct. The particles are ions ($\text{Pb}^{2+}$ and $\text{Br}^{-}$).

b) Lead metal
✅ Correct. The particles are delocalized electrons.

6. The information in the table below relates to the physical properties of the chlorides of certain elements.

a) Explain why melting points of $\text{NaCl}$ and $\text{MgCl}_2$ are higher than those of $\text{SiCl}_4$, $\text{PCl}_3$ and $\text{SCl}_2$ chlorides in the table above.
$\text{NaCl}$ and $\text{MgCl}_2$ are ionic compounds with strong electrostatic forces of attraction between oppositely charged ions in a giant ionic lattice structure. A large amount of energy is required to overcome these strong forces, resulting in high melting points.
$\text{SiCl}_4$, $\text{PCl}_3$, and $\text{SCl}_2$ are covalent compounds that exist as simple discrete molecules. The forces between these molecules are weak intermolecular forces (van der Waals forces). Only a small amount of energy is required to overcome these weak forces, leading to low melting points.

7. $400\text{ cm}^3$ of a gas D diffuses through a porous plug in 50 seconds, while $600\text{ cm}^3$ of oxygen gas diffuses from the same apparatus in 30 seconds. Calculate the relative molecular mass of gas D. ($\text{O} = 16$)