3.5 NOTES: Separating Ions. We can find out which ions are in a solution and separate ions out of solution using 2 methods:

Transcription

1 Chern 12: 3.5 NOTES: Separating Ions We can find out which ions are in a solution and separate ions out of solution using 2 methods: Quantitative analysis (experimental procedures) Precipitation Quantitative analysis Example: we have a solution which we know contains either Ag+ or Ba2+, but we're not sure which. Solution: use the solubility table! 3 Find a A 1 ba ~t ad" 0 (\ 8 ion that will form a _p( f2 (i P \'\a{g + IJ ').~J. one but not the other! This takes some searching! w G\(\~ ~ ~ f < one.,'dn (Ag or Dd,f\ e:l, " An otbers Soluble Sulphate, a I : AU others ~ UQ \ ("\ a\\ 0.\ ~~ Soluble,'1~ c "t, Low Solubility ~J>b+, Cu+ Low SoJubility with il ' ) \.Du) SO I. I t C,\ br or JA We could add ) to precipitate ' e,l( " A 9 ~ c, + ~ A3C\ c s), ta;~ (c).j\) Pp"T UV\ o~/~er j 00 d cho\"c< ~ o 1). ( ppt A3 +)

2 Example 2: A solution is known to contain either Ag+ or Ba2+ ions. (One but not the other). S2 ions are added to this solution and a precipitate DOES NOT FO~ Which ion, (A~+ or!3a2+) is present in the ~ol~tion? ~_ \he... \0(\ \ S ;SO \ \.A'o \ e. \,v \ 1tl S Q ~\ Answer: _Q,Q~ is present in the solution Example 3: You have three beakers each containing a different ion. One has Pb 2; one has ~ eel + and one has Mg 2+ Which is which? Solution:, Start by selecting an anion to add that will only form a ppt with ONE cation.... /~ Chlmide,.T or or ::~/;. \CO" ~ t.o«unc\{( \1 '0..0 So\\..t~)\;\j; ial! otbers Soluble ~:9~~~PP;~PbCi~~~~::~;;,: ~~ Set aside this beaker (label it U1.k;L") Now, add an anion that will form a ppt with only ONE of the remaining cations. CG\?\ ) 09 'Jt A j\ (" '1'.. ~ AU athel.'s Soluble (]\.O Sulphate, so4~ l::'. ~. Ag'" Ca 2 + Sr:!+, 9:1 1 +,'Pb2~ ppl: Co.. SO~ LowSolubitity

3 Set aside this beaker and label it II CIA "~"! l~ ~i ~ p\flo(~\) o{ ~\; m "l\q h on ~ ", You can also label the last beaker Now in reality, we cannot just ADD ANIONS. We can add them in the form of a salt (pair it with a soluble cation). Recall:, {Y: C\ When you want to introduce an a. n, pair it with, When you want to introduce a ca '. n, pair it with + Net +.~ C\clo\ ~ C\ c\.0 A9 f ~ C\tlo~ ~ND3 Example: A solution is known to contain either CI (chloride) ions or S042 (sulphate) ions. Name a compound which you could add to tell you which ion was present. or <; :J Vo\{ Solution: look up these two anions on the solubility table: \.. Chloride.Cl ") AU others Soluble or~ Bromide, Dror, ~~;. Iodide, 1 1 /""""'7 Ai w"+.,.. Cu+ Low " So!ubl1it'l'.r AU others Soluble l Sui, SOil ;= } ;.::: A./ / 2+ IS 2+' 2+. P" 'S 1 Ie '1',/,<1 \:r. <1 Y U LOW 0 Uul Ity.0\.) L ~+ab\l._. wd \ Bad choices of cations to add would be: A..a r?b 'd; (y'\ok. C01,S. /"10+ d. (\ O 'J.1 ~ d ~i +0 (u. L", Good choices of cations to add would be: LlA ) 0( > uct C'V\Cl1t I D ),'{\. vj {,\+< r. So, the compound we add would be:(~cl (ND;JL '\ ~h ~~ )5, (\\) 1)> ( t)o.ll\lo~) L

4 Example. A solution is known to contain either Ba2+ or Mg2+ ions. Suggest a method by which these solutions could be analyzed to find out which ion is present. Be specific about any compounds that are added. Clo..&~~ 0IJL\L. 7 PPt BQl.\ 0("\ \j. \ Ii DD N0. ~ 'SO cf l Example: A solution is known to contain!!.!1: of these.ions; Mg2+, Ca2+, Sr2+, or Be2+: Mixing samples of the solution with various reagents gives the following data: <' d SO'~ I I /"0 ~ '\ ~OM,( ",( Reagent i Na S i Na2S04) i N~H t..,.., "' j ~..= ",, t,, Result i no_ppt. i ppt. i no ppt..... ; From these data, which one of the four ions is present?.. '. ~ 5 :SOl{ d. OH. tv\s 2.,. no ppt no pr\ no ppt CC\ ~t y\ v PPT VPT f\\ D \<. e. o so\v\b ~,\'tj c\t a (t ~ Sf ~~' ~ Be 'J.t PP'T ho ppt rvo ppl

5 Precipitation Methods of Separating Ions ( sa me. as \ as r mett16a) b\.{ r. This method involves forming a precipitate and removing it by filtration. The precipitate remains as a residue rt on the filter paper. The filtrate containsany soluble substances. These are able to penetrate through the filter paper. If there are more ions in the "filtrate", we can repeat the process. Example: You are given a solution containing silver ions (Ag'"), strontium ions (Sr2+), and magnesium ions (Mg2+). You must separate them, one at a time from the solution using precipitation reactions. Show how you would do this. Write the NetIonic Equation for each precipitate formed. Solution: A r. 3 choose an anion that will form a ppt with only ONEcation:. OT C... :hlo...ride..'.cr or Bromide, Br ~ ~dide,l I All others Solu\'lle,.. ',"',,'" o. Low Solubility c;;)pb.t, ell+

6 Step 1: add No.. c, \ to precipitate ~ Net ionic equation: '\ A8 ~t:;)t C\ l~) 7 A 3 c \ (s) (f\u 5\>~L\lI\TO'i',C0») i Filter the solution (the precipitate will remain on the filter paper).. 2r Step 2: add to precipitate Sr. Q ~ \ ~ do. S s r: Net ionic equation: 0( c~) \ 00'4 (luj.) 7 r Vt+ CS) Filter the solution (the precipitate will remain on the filter paper). Step 3: add NL\ 0 tt to precipitate~ 1 (**note: it doesn't matter if you add an anion that precipitates 2 ions, since the other ions are gone. But if you can, choose an anion that just precipitates the ion you want). OH be \\C~ +h a f\ po'} "3 V Net ionic equation: 1v'\9 '~ \Jr) t 20 It ("1) ~ JIllj CD I+)z. U) Filter the solution (the precipitate will remain on the filter paper). Do Questions in Hebden p. 90 #2632, 36, 37