The elements sodium to argon form the third period of the periodic table - Scottish Highers Chemistry - Question 2 - 2018

The structure to circle is that of sulfur chloride (SCl2), as it contains bonds that are more balanced in polarity compared to the other chlorides shown.

Silicon tetrachloride (SiCl4) is non-polar due to its symmetrical tetrahedral shape, which leads to the cancellation of dipoles. In contrast, the other chlorides are polar due to asymmetric structures, making them less compatible with the non-polar solvent hexane. This non-polar nature enhances its solubility in hexane.

Silicon nitride (Si3N4) forms a covalent network structure, consisting of strong covalent bonds that extend throughout the lattice. The strength of these bonds requires a significant amount of energy to break during melting, resulting in a high melting point of 1900 °C.

The atom economy can be calculated using the formula:

$\text{Atom Economy} = \frac{\text{mass of desired product}}{\text{total mass of reactants}} \times 100$

In this case, the molar mass of Si3N4 is 140.3 g and the total mass of reactants (35Cl + 16NH3) amounts to 510.3 g.

Calculating the atom economy:

$\text{Atom Economy} = \frac{140.3}{510.3} \times 100 \approx 27.5\%$

The diagram should include a flask for the reactants, a heating source to heat the aluminium foil, a delivery tube for chlorine gas, and a setup to allow unreacted gas to escape. Labels should include 'Hydrochloric Acid', 'Sodium Hypochlorite', 'Heated Aluminium Foil', and 'Hot Aluminium Chloride Gas'.

The aluminium foil needs initial heating to provide sufficient activation energy for the reaction with chlorine. Even though the reaction is exothermic and will continue once started, an initial energy input is essential to initiate the reaction process.