bue-t red red blue PH test basic DIL Da ysis: An Experimental Plan A Assume you
ID: 1058505 • Letter: B
Question
bue-t red red blue PH test basic DIL Da ysis: An Experimental Plan A Assume you were given asolution that was said tocontain ca-cations only Describe howyou would confirm or deny the presence of this cation in the solution. Explain your reasoning would confirm the presence of the cahon when mixed the Naott solution, an induble calcium hydroxide formed (which happend-y wh Helopaque pot B. Assume you were given a solution that was said to contain zna. and Au cations only Describe how you would determine if neither, only one, or both of these ions were present in solution. Explain your reasoning. C Assume you were given a solution that was said to contain Cu and Co cations only. Describe how you would determine if neither, only one, or both of these ions were present in solution. Explain your reasoning.Explanation / Answer
Q1) When the solution has only Ca+2 ions , we can confirm its presence even by addition of dil. sulphuric acid or oxalic acid solutions , wgich gives a white precipitate of calcium sulphate or calcium oxalate respectively.
Q2) If the solution has either Zn+2 and /or Al+3 ions only, tey can be identified as follows:
i) the solution is treated with NH4Cl followed by ammonia solution , where Al+3 if present would precipitate as a white gelatinous precipitate of aluminium hydroxide.
After removing the precipitate , the filtatrate is tested for Zn+2 ion by addition of aquous NH4Cl, ammonia and H2S which gives a white precipitate of ZnS.
If we get precipitate in both solutions, it shows the presence of both ions.
case ii) only Al+3 present. The gelatinous Al(OH)3 with NH4CL/NH3 but no precipitate with NH4Cl+ NH3 + H2S.
case iii) only Zn+2 present.
With addition of NH4CL and ammonia to the solution no gelatinous precipitate observed. Shows the absence of Al+3. then to the same solution H2S is passed, which gives a white precipitate of Znhydroxide.
Q3) If the solution has both Cu+2 and Co+2
case i) Both ions present
To the salt solution first dil. Hcl and H2S are added , a black preicipitate of CuS shows the presence of copper ion.
Then after completely precipitating all coppper as Cus, the precipitate is filtered and the clear filtate is taken and added with a little excess of NH4Cl/NH3 and H2S gas is passed into it. again a balck preipitate of CoS is formed.
Though, both Cu+2 and Co+2 are precipitated as bacl sulpjides, thier precipitation is done in acidic and basic media respectively.
CuS has very low Ksp value thus requires less [S-2] where as CoS needs much higher [S-2] in solution due its high ksp value.
Thus for Cu+2 ion H2S is used in acidic medium where the quilibrium
H2S <---> 2H+ + S-2
is shifted backwards due to the common ion H+ , thus providing low [S-2}
For Co+2 a slighly basic medium is used, which makes the H2S equillibrium shiftng to the right side to give higher concentration of S-2 to precipitate CoS.
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