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Halogens
Unit 2 AQA A Level Chemistry
| Question | Answer |
|---|---|
| Size of atoms going down the group? | Atoms get bigger going down the group due to increasing no.s of main energy levels |
| Electronegativity going down the group? | Electronegativity decreases down the group as the shared pair of e- get further away from the nucleus and shielding increases as the no. of main energy levels increases |
| Melting/boiling points down the group? | Melting/boiling points increase down the group because down the group no. of e- increases so van der Waals forces between molecules get stronger |
| Oxidising power going down the group? | Oxidising power decreases down the group- fluorine is an incredibly powerful oxidising agent. |
| Displacement trend? | The halide in a compound will be displaced by a more reactive (higher up the group) halogen |
| Reducing power of the halides going down the group? | Reducing power of the halides increases down the group (larger ions more easily lose e-) |
| Sodium chloride + hot conc. sulphuric acid: Observation? Redox reaction? | Steamy fumes hydrogen chloride,solid sodium hydrogensulphate formed. Is not a redox reaction as choride ions v.weak reducing agents |
| Sodium bromide + hot conc. sulphuric acid: Observation? Redox reaction? | Steamy fumes hydrogen bromide, brown bromine fumes, colourless sulphur dioxide. Redox. |
| Sodium iodide + hot conc. sulphuric acid: Observation? Redox reaction? | Steamy fumes hydrogen iodide, black solid iodine, hydrogen sulphide gas, yellow solid sulphur, colourless sulphur dioxide. Redox. |
| Method to identify metal halides? | Dilute nitric acid added to remove impurities (e.g carbonate or hydroxide ions). Few drops silver nitrate solution added. |
| Silver nitrate test result for FLUORIDE ions | No ppt. |
| Silver nitrate test result for CHLORIDE ions | White ppt. Dissolves in dilute ammonia. |
| Silver nitrate test result for BROMIDE ions | Cream ppt. Dissolves in conc. ammonia. |
| Silver nitrate test result for IODIDE ions | Yellow ppt. Does not dissolve in conc. ammonia. |
| Reaction equation for chlorine with water | Cl2 + H2O <---> HClO + HCl |
| Define disproportionation | When the oxidation state of some atoms of the same element increases and in others decreases. |
| Reaction equation for chlorine with water in sunlight | 2Cl2 + 2H2O ---> 4HCl + O2 |
| Reaction equation for sodium chlorate added to water | NaClO + H2O <---> Na+ + OH- + HClO |
| Reaction equation for chlorine with an alkali | Cl2 + 2NaOH ---> NaClO + NaCl + H2O |