The elements in Group 17 of the Periodic Table are called the halogens. They form stable compounds with both metals and non-metals. The table gives some data about F2, HCl and CaF2. F2 | HCl | CaF2 --- | --- | --- boiling point/K | 85 | 188 | 2773 relative formula mass | 38.0 | 36.5 | 78.1

1. (a)(i)State what is meant by the term relative formula mass.[2]
2. (a)(ii)F₂ and HCl are both covalent molecules. Suggest why the boiling point of HCl is higher than that of F2.[2]
3. (a)(iii)Explain why CaF2 has a very high boiling point.[1]
4. (a)(iv)CaF2(aq) can be made by the reaction of calcium carbonate with hydrofluoric acid, HF(aq). Write an equation for this reaction. Include state symbols.[2]
5. (b)(i)Complete the electronic configuration of a chloride ion. 1s² .................................[1]
6. (b)(ii)When Cl₂ is passed over hot iron, FeCl3 is formed. However, when I₂(g) is passed over hot iron, the following reaction occurs. Fe(s) + I2(g) → FeI₂(s) State what you would observe during the reaction between Fe and I2. Explain why FeI₂(s) is formed rather than FeI3(s). observation explanation[2]
7. (b)(iii)FeI₂ is soluble in water. A student carries out a chemical test to confirm that a solution of FeI₂ contains aqueous iodide ions, I-(aq). The student adds a single reagent and a precipitate forms. Identify the reagent the student uses. State the colour of the precipitate that forms. reagent colour of precipitate[2]
8. (b)(iv)Compounds containing I- are often contaminated by bromide ions, Br⁻. Identify a further reagent that the student could use to show that the precipitate formed in (iii) contained iodide ions.[1]
9. (c)(i)HOF is the only known molecule that contains only the elements hydrogen, oxygen and fluorine. Draw a 'dot-and-cross' diagram to represent the bonding in a molecule of HOF. Show the outer shell electrons only. [Figure 2.1: Diagram space for dot-and-cross diagram of HOF][2]
10. (c)(ii)HOF can be made by the reaction of F2 with ice at –40°C. The reaction is similar to the reaction of Cl₂ with cold water. Suggest an equation for the reaction of F2 with ice.[1]
11. (c)(iii)HOF is an unstable compound and decomposes to form HF and O2. HOF → HF + ½O₂ ΔH = –139 kJ mol⁻¹ Draw a fully labelled reaction pathway diagram on the axes provided to show the decomposition of HOF into HF and O2. [Figure 2.2: Diagram axes for reaction pathway diagram][2]
12. (c)(iv)Pure HF is a colourless liquid at 273K. The liquid contains HF molecules that have strong hydrogen bonds between them. Draw a fully labelled diagram to suggest how a hydrogen bond can form between two HF molecules. [Figure 2.3: Diagram space for hydrogen bond between HF molecules][3]
13. (d)(i)Interhalogen compounds, such as BrCl or IF5, contain two or more different halogen atoms that are covalently bonded. D is an interhalogen compound that contains only chlorine and fluorine. At 0°C and 101325 Pa, 1 dm³ of D has a mass of 4.13g. Use the general gas equation to calculate the relative molecular mass, Mᵣ, of D. Mᵣ = ...........................................................[3]
14. (d)(ii)Use your answer to (i) to determine the molecular formula of D. If you were unable to calculate the Mᵣ in (i), assume that the Mᵣ is 130.5. This is not the correct value. molecular formula of D = ...............................[1]

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