posted by Amanda on .
how do you know which halide salts confirms a presence of F- ions, Cl- ions, Br- ions, and I- ions?
Amanda--I must admit that I don't have the slightest idea what you are asking. Is there some added information you have that might help?
im sorry.. i don't even know how to ask. maybe if i knew what i was doing i could ask. but we did a lab about halide ions. we used NaF, CaCl, NaBr, and NaI. we used reagents Ca(NO3)2, AgNO3, NH3(aq), Na2S2O3, and starch + NaOCl. we had to tell if a precipitate formed and the color it changed to. and then the first question asks.. which procedures confirms the presence of a. F- ions b. Cl- ions c. Br- ions d. I- ions.
maybe that will help? i have no clue what to do.
I don't know the order in which these test were done; however, here is some back ground that may help you get started.
CaF2 is insoluble in water; therefore, CaCl2 + F^- gives a white ppt.
AgNO3 reacts with Cl^-, Br^- and I^- producing AgCl (white ppt), AgBr(pale yellow ppt), and AgI(a darker yellow ppt). AgCl is soluble in NH3, AgBr is slightly soluble in NH3, and AgI is not soluble in water.
NaOCl reacts with I^- to produce I2 (iodine) which turns a VERY DARK blue (if there is very much I2 there it will be so dark it will look black) when stach is added. The color is removed with Na2S2O3.
There should be enough information here to allow you to pick and choose, either individually or in combination, what you need. For example, the confirmation test for Cl^- is treatment with AgNO3, add NH3, the WHITE ppt dissolves completely. (I don't call the treatment with AgNO3 as part of the confirmation but the AgNO3 must be added to obtain the AgCl which then can be used in what I call the confirmation test. Your teacher probably gave you some instructions that should be helpful here. Another confirming test, for I^-, treat some of the sample with NaOCl, add starch, a dark blue to black color which disappears upon addition of Na2S2O3 confirms the presence of iodide ion.