iGCSE Chemistry 0620 Extended - 10.1 Water- Exam Style Questions Paper 4- New Syllabus
Question
The elements in Group VII of the Periodic Table are known as the halogens. Halogens can form halide ions.
(a) Identify the halogen with the lowest density at r.t.p. (room temperature and pressure).
(b) State the appearance of bromine at r.t.p.
(c) Use the Periodic Table to:
● give the symbol of the halogen with the highest atomic number
● deduce the number of occupied electron shells in an atom of this element.
(d) Bromine molecules have covalent bonding.
(i) State what is meant by the term covalent bond.
(ii) Name one halide ion which bromine molecules can displace.
(iii) Explain why bromine can displace the halide ion in (d)(ii).
(e) Name a halide compound which can be used to detect the presence of water.
(f) Calcium chloride is an ionic compound. Complete the dot-and-cross diagram in Fig. 2.1 for the ions in calcium chloride. Give the charges on each of the ions.
(g) Aqueous lead(II) ions are added to aqueous chloride ions. A white precipitate of insoluble lead(II) chloride, \(PbCl_2\), is formed.
(i) Name a lead(II) compound which can be used in this reaction.
(ii) Write the ionic equation for this reaction. Include state symbols.
(iii) Name one other insoluble chloride.
Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):
• Topic 8.3 — Group VII properties (Parts a, b, c, d)
• Topic 2.5 — Simple molecules and covalent bonds (Part d(i))
• Topic 10.1 — Water (Part e)
• Topic 2.4 — Ions and ionic bonds (Part f)
• Topic 12.5 — Identification of ions and gases (Part g)
▶️ Answer/Explanation
(a) Fluorine (F₂) is the halogen with the lowest density at r.t.p. As we move down Group VII, both atomic mass and atomic size increase, leading to a steady increase in density from fluorine to astatine. Fluorine is a gas with very low density.
(b) Bromine appears as a red-brown liquid at room temperature and pressure. It is the only non-metal that is liquid at r.t.p., with a characteristic deep reddish-brown color and volatile nature.
(c) Tennessine (Ts) is the halogen with the highest atomic number (117). It has 7 occupied electron shells because it is in Period 7 of the Periodic Table, meaning its electrons fill shells 1 through 7. Ts is a synthetic superheavy element.
(d)(i) A covalent bond is formed when a pair of electrons is shared between two atoms. This sharing allows each atom to achieve a stable noble gas electronic configuration, usually a full outer shell of 8 electrons (octet rule).
(d)(ii) Bromine molecules can displace iodide ions (I⁻). In the displacement reaction, bromine (more reactive) oxidizes iodide to iodine while itself being reduced to bromide ions.
(d)(iii) Bromine can displace iodide because bromine is more reactive (higher in Group VII) than iodine. Reactivity decreases down Group VII, so a more reactive halogen will displace a less reactive halide from its compound.
(e) Anhydrous cobalt(II) chloride (CoCl₂) is a blue halide compound used to test for water. It turns pink in the presence of water, forming hydrated cobalt(II) chloride (CoCl₂·6H₂O).
(f) The dot-and-cross diagram for calcium chloride (CaCl₂) shows: a Ca²⁺ ion with its 4th shell empty (8 crosses in the 3rd shell for [Ar] configuration, but commonly drawn with no outer electrons after losing 2 e⁻). Each Cl⁻ ion has 8 outer electrons (7 original + 1 gained), shown as 7 dots and 1 cross (or vice versa) around each Cl with a full octet. The charges are ‘2+’ on calcium and ‘-‘ on each chloride ion.
(g)(i) Lead(II) nitrate [Pb(NO₃)₂] is a soluble lead(II) compound commonly used to provide Pb²⁺ ions in precipitation reactions because it mixes well with other aqueous solutions.
(g)(ii) Pb²⁺(aq) + 2Cl⁻(aq) → PbCl₂(s). The ionic equation shows only the reacting ions forming the solid precipitate, omitting spectator ions. State symbols indicate aqueous ions and solid product.
(g)(iii) Silver chloride (AgCl) is another insoluble chloride. Like PbCl₂, it forms a white precipitate when silver ions are added to chloride-containing solutions, and it is used in qualitative analysis to identify Cl⁻ ions.