Question

I concluded that my unknown was Pb2+. since yellow precipitate formed. can you help me answer the questions for the Known and unknown report

Qualitative Analysis: Group I Cations 10 ORECTIVES A Leam some chemistry of Group I cations, R Analyze an unknown for Group I cations. THEORY AND DISCUSSION Group I cations are precipitated as insoluble chlorides: Ag, Pb, Hg2 +Cr-AgCl, PbCh, HgCla The colors of the following species will be helpful in the analysis for Group I cations. NOTE: because of the toxicity of mercury, you must wear gloves for this experiment. Note: Assume ions noted below are dissolved in water (aq) and compounds exist as precipitates (s). Ag AgCl Ag(NHs) (colorless) (white)* (colorless) Ph РЬС |РЬСО. (colorless) (white) (yellow) (colorless) (white) (black) (white) Hg Ch |Hе HgNH:C darkens on exposure to light EXPERIMENTAL PROCEDURES Group separations are designated GS1, GS2, ete. Specific confirmation tests are designated ST1, ST2, etc. Tests using knowns t be run alongside unknowns. See grading guidelines in the Introduction to Qualitative Analysis. GSI, SEPARATION OF GROUP I IONS, Ag, Hg, Pb hiryour knowns, prepare a combined mixture of 5 drops each of the AgNO, Pb(NO), and HgNO, knowns and treat them parallel with the unknown. To I ml. of test solution (knowns or unknowns) add 2 drops of 6M HCI. Mix, centrifuge and ad drop more of 6M HCL. If precipitation is not complete, mix and add another drop. Continue, if necessary, drop by drop ht try to avoid more than 1 drop excess to prevent complex chloride formation by Ag' or Pb which would allow them to pass through to Group 2. If no precipitate forms, Group I ions are absent. By centrifugation separate, remove, and save the trate for analysis of subsequent groups if you are running the general unknowns (lab practical Exxperiment 13), Wash the recipitate and add the first 1 ml of cold wash water to the filtrate. Wash the precipitate once more with cold wash water ad discard the wash solution. STI, Pb To the residue (precipitate) from GSI which may contain AgCl, HgClh and PbCl, add 2 ml of water and heat to boiling in a water bath with mixing. Allow the precipitate to settle, withdraw and save the clear solution for a Pb test. Again add 2 mL of water to the residue, heat and mix and discard the filtrate. Repeat once more to remove the last traces of lead. Save the residue for ST2 and ST3, To the cooled filtrate for the Pb test add 3 drops of IM K;CrO A yellow precipitate of PhCrO, confirms Pb. The yellow precipitate is soluble in strong base. Note: traces of Ag' ion can yield silver chromate, AgCrO, a dark orange precipitate. 129 C T

Answer 1

For known

Sample - given compound

Reagent 6M HCl

Procedure:

Same as given in problem

Observation:

Yellow ppt formed

Conclusion: Given unknown conatins Pb2+ as it gives yellow ppt with HCl

equation:

Pb2+ + HCl------> PbCl2 (yellow)

For unknown all same

only ppt color changes

AgCl-White

and so on as given in problem