Home / iGCSE Chemistry (0620) Theory (Core):8.3 Group VII properties: Exam Style Questions Paper 3
(a) Table 5.1 shows some properties of five halogens.
Use the information in Table 5.1 to predict:
(i) the melting point of astatine
(ii) the atomic volume of fluorine
(iii) the physical state of fluorine at −240°C. Give a reason for your answer.
(b) Aqueous chlorine reacts with aqueous sodium iodide.
(i) Complete the word equation for this reaction.
(ii) Explain why aqueous bromine does not react with aqueous sodium chloride.
(c) Fluorine reacts with water to produce hydrogen fluoride and oxygen.
Complete the symbol equation for this reaction.
\[ 2F_2 + \ldots H_2O \rightarrow 4HF + \ldots \]
(d) Name an anhydrous compound used to test for water. State the colour of the compound after water is added.
Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):
• Topic 8.3 — Group VII properties (Parts (a), (b))
• Topic 10.1 — Water (Part (d))
(a)(i) Between 116°C and 335°C (inclusive)
Looking at the trend in melting points down Group 17 (halogens), we see they increase: F (-220°C), Cl (-101°C), Br (-7°C), I (114°C). Astatine, being below iodine, would have a higher melting point than iodine but lower than its boiling point of 337°C.
(a)(ii) Less than 22.7 cm³/mol (but not below 1.0)
The atomic volume increases down the group: Cl (22.7), Br (25.6), I (25.8), At (32.8). Fluorine, being above chlorine, would have a smaller atomic radius and thus a smaller atomic volume.
(a)(iii) Solid, because −240°C is below fluorine’s melting point of −220°C.
At temperatures below its melting point, a substance exists as a solid. Since −240°C is 20 degrees below fluorine’s melting point (-220°C), it would be solid.
(b)(i) iodine + sodium chloride
This is a displacement reaction where the more reactive chlorine displaces iodine from sodium iodide. The products formed are iodine (which colors the solution brown) and sodium chloride.
(b)(ii) Bromine is less reactive than chlorine / chlorine is more reactive than bromine.
In the reactivity series of halogens, reactivity decreases down the group. Chlorine is above bromine, meaning it can displace bromine, but bromine cannot displace chlorine from its salts.
(c) 2, O₂ (Resulting equation: 2F₂ + 2H₂O → 4HF + O₂)
This is a redox reaction. Balancing requires 2 water molecules to provide 4 hydrogen atoms for the 4 HF molecules and 2 oxygen atoms to form 1 O₂ molecule. Fluorine is reduced (0 to -1), oxygen is oxidized (-2 to 0).
(d) Copper(II) sulfate → blue OR Cobalt(II) chloride → red/pink.
Anhydrous copper(II) sulfate is white and turns blue when it absorbs water to become hydrated copper(II) sulfate. Anhydrous cobalt(II) chloride is blue and turns pink upon hydration.