Please answer #3 I provided background of the lab directions in order to answer

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Please answer #3 I provided background of the lab directions in order to answer it WSlver Group OBJECTIVE solution. BACKGROUND To identify which "Group I" cations (Ag'.Pi', and Hg,") are present in an unknown The Group I cations, Ag". Pb, and Hg,"are the only common cations that form insoluble chlorides in dilute hydrochloric acid. (Note that the qualitative analysis designation "Group I" does not refer to the alkali metal group of the periodic table.) This allows the Group I cations to be separated from other cations in solution by ad- dition of HCL The net-ionic equations for the precipitation that occurs are shown directly below. Although all three metal salts are poorly soluble in pure water at room temperature PbCl, is significantly more soluble than Hg,Cl, and AgCl in hot water. This increase in solubility on heating is the basis of separating PbCl, from the AgCl and Hg,CL The net-ionic equation for the dissolution of PbCl, is: Lead ion is confirmed by adding K,CrO, to the test solution which precipitates yellow lead chromate. 4 (aq)

Explanation / Answer

Hg2 (NO3)2 and Mg (NO3 )2 solution-------------------------reagent ----- Aqueous ammonia

When aqeous NH3 is added to Hg2 (NO3)2 solution the following reaction occurs forming insoluble white precipitate which does not dissolve in excess of NH3

2Hg2+  + 4NH3 (aq) + NO3 (aq) + H2O -----------> Hg (l) + Hg2 O NH2 NO3 (s) + 3NH4+ (aq)

-----------------------------------------------------------------------------------------(-white ppt. of amido salt) -------------------------

but with Mg(NO3)2 the white ppt. of Mg(OH)2 is soluble in excess of ammonia

reactions are,

NH3 + H2O ------------------> NH4OH -----------------------------> NH4+   + OH-   

Mg(NO3)2 + 2OH-   -------------------> Mg(OH)2 + 2NO3-   

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Hg2 Cl2 & AgCl solids -------------------------------------Reagent ----------------------aqueous ammonia solution----------------

The aq. ammonia solution reacts to form a black precipitate with Hg2Cl2 solid while solid AgCl would dissolve in excess of ammonia solution. The following reactions occur separately.

Reaction with Hg2Cl2 with ammonia is a disproportion reaction liberating free Hg along with Hg complexes of variable composition, as follows-

Hg2Cl2 ------------------------------> Hg Cl2 + Hg

HgCl2 further reacts as follows

HgCl2 + 2NH3(aq) <------------------> [ Hg (NH3 )2 Cl2 ] + NH4Cl

[ Hg ( NH3 )2 Cl2 ] <--------------> [ Hg NH2 Cl ] + NH4Cl

Hg NH2 Cl + H2O <---------------------------> [ Hg2 N Cl [ H2 O ] + NH4Cl

Reaction of excess NH3 (aq) with solid Ag Cl -----

AgCl (s) + NH3 (aq ) ====> Ag (NH3)2+   + Cl-   

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Na2 Cr O4 & HCl solutions -------------------------reagent ------- ( CH3 COO ) 2 Pb solution-------------------

When lead acetate solution is added to Na2 CrO4 solution a yellow precipitate of lead chromate is seen

Na2CrO4 + ( CH3 COO ) 2 Pb -----------------------------> Pb Cr O4 + 2CH3 COO Na

but when this reagent is mixed with HCl solution a white precipitate of lead chloride( PbCl2 ) results

(CH3COO)2 Pb + 2HCl --------------------> PbCl2 + 2CH3COOH

This ppt. is soluble in hot but insoluble when cold.

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Hg

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