Home / AS & A Level Chemistry 9.3 Chemical periodicity of other elements Exam Style Practice Questions Paper 1
Q is a semi-conductor. The chloride of Q reacts with water to form white fumes and an acidic solution.
Which Period 3 element is Q?
Correct Answer: \( \boxed{\mathrm{C}} \)
Silicon is the only semiconductor among the Period 3 elements listed.
Its chloride, \( \mathrm{SiCl_4} \), reacts readily with water:
\( \mathrm{SiCl_4 + 2H_2O \rightarrow SiO_2 + 4HCl} \)
The hydrogen chloride produced forms white fumes in moist air, and the dissolved \( \mathrm{HCl} \) makes the solution acidic.
Therefore, Q is silicon.
What are the acid–base nature and structure of \( \mathrm{SO_2} \)?
| acid–base nature | structure | |
|---|---|---|
| A | acidic | giant covalent lattice |
| B | acidic | simple molecular |
| C | basic | giant covalent lattice |
| D | basic | simple molecular |
Correct Answer: \( \boxed{\mathrm{B}} \)
Acid–base nature:
\( \mathrm{SO_2} \) is an acidic oxide. It dissolves in water to form sulfurous acid:
\( \mathrm{SO_2 + H_2O \rightleftharpoons H_2SO_3} \)
Structure:
\( \mathrm{SO_2} \) exists as simple molecular molecules. Each molecule has a bent (V-shaped) geometry due to the presence of one lone pair on the sulfur atom.
It is not a giant covalent lattice.
Therefore, the correct combination is acidic and simple molecular, so the correct answer is (B).
Elements X and Y are in Period 3 of the Periodic Table. Element X is either phosphorus or sulfur. Element Y is either sodium or magnesium.
Element X forms an oxide that reacts with water to give a solution containing the aqueous anion \( \mathrm{XO_4^{2-}} \).
One mole of element Y reacts with one mole of chlorine molecules. At the end of the reaction, all of the element Y and all of the chlorine molecules have been used up.
What are elements X and Y?
| X | Y | |
|---|---|---|
| A | phosphorus | sodium |
| B | phosphorus | magnesium |
| C | sulfur | sodium |
| D | sulfur | magnesium |
Correct Answer: \( \boxed{\mathrm{D}} \)
Identifying X:
Sulfur forms the oxide \( \mathrm{SO_3} \), which reacts with water to produce sulfuric acid:
\( \mathrm{SO_3 + H_2O \rightarrow H_2SO_4} \)
In aqueous solution, sulfuric acid dissociates to give sulfate ions, \( \mathrm{SO_4^{2-}} \). Phosphorus(V) oxide reacts with water to form phosphoric acid, which contains phosphate ions, \( \mathrm{PO_4^{3-}} \).
Therefore, X is sulfur.
Identifying Y:
The reaction must use one mole of metal and one mole of chlorine:
\( \mathrm{Mg + Cl_2 \rightarrow MgCl_2} \)
Sodium reacts according to:
\( \mathrm{2Na + Cl_2 \rightarrow 2NaCl} \)
This requires 2 moles of sodium for every mole of chlorine, so it does not satisfy the condition.
Therefore, Y is magnesium, and the correct answer is (D).