The test solution is made acidic with nitric acid, and then Silver nitrate solution is added dropwise The role of nitric acid is to react with any carbonates present to prevent formation of the precipitate Ag2CO3. This reaction is used as a test to identify which halide ion is present. The reactions of halide ions with silver nitrate. The colour of the halogen solution will fade to colourless Cl2 (aq) + 2NaOH(aq) NaCl (aq) + NaClO (aq) + H2O(l) The mixture of NaCl and NaClO (sodium chlorate (I)) is used as Bleach and to disinfect/ kill bacteria If the hot sodium hydroxide is used a different disproportionation reaction occurs forming sodium chlorate (v) 3Cl2 + 6NaOH → NaClO3 + 5NaCl + 3H2Oĩ 3. The chlorine is reacting by disproportionation. Ĩ Reaction of Chlorine with cold dilute NaOH solution:Ĭl2 ,(and Br2, I2 ) in aqueous solutions will react with cold sodium hydroxide. The benefits to health of water treatment by chlorine by its killing of bacteria outweigh its risks of toxic effects and possible risks from formation of chlorinated hydrocarbons. It has been used to treat drinking water and the water in swimming pools. It changes from 0 in Cl2 to -1 in HCl and +1 in HClO Chlorine is used in water treatment to kill bacteria. It will then turn colourless as the HClO bleaches the colour Chlorine with water: Cl2 (aq) + H2O(l) HClO(aq) + HCl (aq) Chlorine is both simultaneously reducing and oxidising. If some universal indicator is added to the solution it will first turn red due to the acidity of both reaction products. The disproportionation reactions of chlorine and chlorate(I).ĭisproportionation is the name for a reaction where an element simultaneously oxidises and reduces. The is because an atom of chlorine is smaller than bromine and the outermost shell of chlorine is less shielded than bromine so the electron to be gained is attracted more strongly to the nucleus in chlorine than bromine. Chlorine = colourless Bromine = yellow Iodine = purpleĬhlorine is more reactive than bromine because it will gain an electron and form a negative ion more easily than bromine. The colour of the organic solvent layer in the test tube shows which free halogen is present in solution. Chlorine =very pale green solution (often colourless), Bromine = yellow solution Iodine = brown solution (sometimes black solid present)ĥ Observations if an organic solvent is added They therefore form -1 ions less easily down the group The colour of the solution in the test tube shows which free halogen is present in solution. The reactivity of the halogens decreases down the group as the atoms get bigger with more shielding so they less easily attract and accept electrons. This increases the melting and boiling pointsĤ The displacement reactions of halide ions by halogens. As the intermolecular forces get larger more energy has to be put into break theses intermolecular forces. Increase down the group as the molecules become larger they have more electrons and so have larger induced dipole-dipole forces (London forces) between the molecules. It is highly reactive Chlorine : (Cl2 ) greenish, reactive gas, poisonous in high concentrations Bromine (Br2 ) : red liquid, that gives off dense brown/orange poisonous fumes Iodine (I2 ) : shiny grey solid sublimes to purple gas.ģ Trend in melting point and boiling point Presentation on theme: "HALOGENS PRECIOUS."- Presentation transcript:Ģ GROUP 7: All halogens exist as diatomic moleculesįluorine (F2 ): very pale yellow gas.
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