Group 7 trends and halogen reactionsEdexcel International A Level Chemistry: Mind map

Exam questions on Group 7 trends and halogen reactions

1. The melting and boiling temperatures of three halogens are: chlorine, Cl₂, melting 172 K and boiling 239 K; bromine, Br₂, melting 266 K and boiling 332 K; iodine, I₂, melting 387 K and boiling 457 K. Room temperature is taken as 298 K.
   Explain why the boiling temperature increases from chlorine to iodine.2 marks
2. A student adds a few drops of aqueous halogen solutions to separate aqueous solutions of potassium halides. She then adds a few cm³ of hexane to each tube, shakes it and leaves the layers to separate.
   Write the ionic equation for the reaction of aqueous bromine with aqueous iodide ions, and identify the oxidising agent.2 marks
3. A swimming pool is treated with chlorine to kill bacteria. A manufacturer makes bleach by passing chlorine into cold dilute aqueous sodium hydroxide, forming sodium chloride and sodium chlorate(I), NaClO. When the sodium hydroxide is hot and concentrated, sodium chlorate(V), NaClO₃, forms instead of NaClO.
   Write the equation for the reaction of chlorine with water. Use oxidation numbers to show that this is disproportionation, and state why it is useful in treating water.3 marks