DIscussion of reactions of halides in solution
MV：Types of halides used. RV：Reactions of halides in solution with certain reagents & products formedin the reactions.
PartA&B: Silver nitrate solution is added into potassium halide solutions(KCl KBr KI) and double displacement is happens. The silver sil ver halides(AgCl Agbr AgI), which are insoluble salts will precipitated in the solution(KNO3) as they cannot dissolve in water. KNO3 solution is also a product of the reaction which is a colourless solution.The product ,silver halides is a photosensitive substance.When substance.When is exposed to light l ight with UV ,it will decomposes to form a elemental silver and halogen gas.Expose to the sunlight which contain high intensity of UV light ,the process of decompose is very fast .The effect of common light indoor is same but the reaction will be much slower. For the reaction between KCl and AgNO3, a
white precipitate is
formed in the colourless solution. The colourless solution is the KNO3 solution while AgCl is the white precipitate. The chemical equation : KCl (aq) + AgNO3 (aq) -> KNO3 (aq) + AgCl(s). In dark condition, the colour of solution is milky white and precipitate is silver. However,when it is put
under light,colour of solution is milky and precipitate is white.Theoritically, AgCl is very sensitive to light and will decompose into Ag and Cl, with an equation of: 2AgCl (s) +light -> 2Ag(s) + Cl2 (g). This will forms a grey solution with grey precipitate, which is Ag (s). When KBr reacts with AgNo3, a pale yellow colour precipitate with milky white solution is formed. The chemical equation is KBr (aq) + AgNO3 (aq) -> KNO3 (aq) + AgBr(s). The solution is KNO3 while the pale yellow precipitate is the insoluble salt , AgBr. In dark condition, the precipiitate is pale green and solution is milkky pale green.. When it is put under light, AgBr decompose into Ag and Br, with an equation of: 2AgBr (s) +light ->2Ag(s) + Br2 (g). There are only slight changes in the intensity of the colour of precipitateand solution, this is because AgBr is less sensitive to light compared to AgCl. Greenish yellow solution and pale yellow precipitate is formed when KI reacts with AgNO3. The chemical equation is KI (aq) + AgNO3 (aq) -> KNO3 (aq) + AgI (s). KNO3 is the greenish yellow solution while AgI is the insoluble pale yellow precipitate. In dark condition,milky yellowish solution and pale yellow precipitate was formed. At light condition, there are only slight changes in the intensity of colour, this is because AgI is less sensitive to light too if compare with AgCl and AgBr. AgI decomposes into Ag and I under light condition, the equation is:2AgI (s) +light -> 2Ag(s) + I2 (g).
Part C Potassium halides(KCl KBr KI) was added with silver nitrate followed by diluted HNO3.The solution was acidified by adding dilute nitric acid.The nitric acid will react with and removes other ions that might also give a confusing precipitate with silver nitrate solution.Thus, the silver ions are added in the form of acidified silver nitrate solution as this is one of the few soluble silver salts.The nitric acid is there to decompose if carbonate ions or sulfite ions present,which interfere with the test and give a false positive white precipitate of silver carbonate. 2Ag+ + CO3-
----->Ag2 + CO3
~~~~~~~(observation?)~~~~~~~
Part D Potassium halides(KCl KBr KI) is react with silver nitrate followed byNH3.This is because the ammonia molecules present in the ammonia solution will form a complex ion with silver(1）ions which then allows the precipitate to re-dissolve.The ammonia combies with silver ions to
produce a complex ion called diamminesilver (1)ion,[Ag(NH3)2]+. This is a reversible reaction but the complex ions is more stable and the position of equilibrium lies to rght. Ag+（aq) +2NH3(aq) <--------> [Ag(NH3)2]+(aq) However the ease with which this happens depends on the nature of the halides.AgCl can forms complex ion easily in dilute ammonia suffices: NH3 + AgCl --> [Ag(NH3)2]+ + Cl-.The silver complex ion, diammine silver(I), is a linear ion with the ammonia ligands arranged at 180 degrees to one another.The original precipitate ,AgCl will dissolves to give a colourless solution when ammonia is added. Silver bromide also dissolves in ammonia, but only if the ammonia is in concentrated solution.NH3 + AgBr --> [Ag(NH3)2]+ + Br-.When ammonia is added to AgBr precipitate ,the precipitate is almost unchanged using diluted ammonia solution ,but dissolves in concentrated ammonia solution to give a colourless solution. Silver Iodide precipitate is insoluble in any concentration of ammonia solution. ~~~(observation?)~~~
PartE
~~~ Chemical test distinguish halogen ions The chemmical test to distinguish between Cl- Br- I- is by using silver nitrate solution.this testmust be done in solution, a solid can must be dissolved in distilled water before test.The solution is acidified by using diluted nitric acid to react and remove other ions such as carbonate ion and sulfite ion that might give a confusing precipitate with silver nitrate.Then,silver nitrate solution is added to each solution that contain different halide ions which is Cl- Br- I-.If Cl- present white ppt will formed If Br- is present,pale cream ppt will formed.If I- present,pale yellow ppt will formed.
Darkening effect Darkening effect of light on silver chloride and silver bromide ppt occured as uv light converts a part of silver halide into matallic silver which is dark in colour ppt.for an example ,lenses of the spectacles contain small amount of white , finely spread silver chlorides on it returned back to sunlight ,some of the Ag+ions on the lenses convert into Ag metal.This reaction is reversible as back to dark condition,AgCl and Agbr will reformed and glass become clear again.
AgBr is less sensitive to light than AgCl 2AgCl(s)+light --> 2Ag(s) + Cl2(g) Precaution steps There are several precautions steps to obtain a more accurate result.The test tube containing solution must be transferred to dark cupboard immediately to ensure silver halide not exposed to uv light.This is because silver halides are photosensitive.The test tube must be stoppered with a cork after addition of any solution to prevent the gas to escape which is a part of result and also help to avoid contact of chemical with skin when shaking the test tubes.Besides the observatio of the test tubes taken out from dark cupboard should be recorded immediately as silver halides will react with the light immediately.The test tubes should be place infront of a white paper when observed the colour of the solution.Besides to obtain the most accurate result of the action of silver nitrate with sunlight,the silver halides should be exposed to the light with high intensity of uv light such as sunlight or the burning of magnessium ribbon because the effect of common light will be much slower.
Conclusion ~~
