posted by Anonymous .
A Solution contains a mixture of Cl- and Br- ions. Can both be positively identified? Briefly explain. Write appropriate equations to support your answer.
Yes they can. Anyone who has done a qualitative analytical scheme will know how to do this. But I'm not about to write a 30 minute script. I'll be glad to help if you wish to identify exactly what you need help with.
What I have with is really figuring out the equation. I know that in the presence of AgNO3, the Cl- would form AgCl which forms a precipitate.
The Br- would form (BrNO3)+2 or something like that.
I feel like I'm on the right track here but I'm doing something wrong.
The equation I'm thinking of is:
Cl-(aq) + Br-(aq) + AgNO3(aq) <-----> AgCl (ppt) + BrNO3(aq)
AgNO3 will ppt BOTH AgCl and AgBr; AgBr is the more insoluble. Without going into great detail here is what is done in the analytical lab to detect (and confirm both).
To detect Br^-, take a small amount of the solution, add NaOCl and several drops hexane, shake thoroughly. A yellow/pale orange color indicates bromide ion.
To another portion of the sample, acidify with dil HNO3, add AgNO3 until pptn is complete. This will ppt both AgBr and AgCl. If a ppt occurs and no bromide was detected (and there is no iodine), a white ppt shows the presence of Chloride ion. If bromide is present, add a mixture of NH3/KNO3 (Miller's Reagent). This reagent dissolves AgCl but not AgBr. Separate the solid and discard (throws the AgBr away). Acidify the liquid with dil HNO3; the formation of a white ppt proves the presence of chloride.
I will leave the equations to you but the most important are these.
Ag^+ + Br^- ==> AgBr(s)
Ag^ + Cl^- ==> AgCl(s)
Br^- + OCl^- ==> Br2 (which in hexane looks yellow to pale orange).
Ag^+ + 2NH3==> Ag(NH3)^+(aq)
Randomly came upon this ask thread.... LOL "Dr" Bob is one SOB. What a jerk.