PHA612-Lab - Expt 4 - Reactions and Analysis of Group 1 Cations PDF

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Reactions and Analysis of Group 1 Cations...

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University of Santo Tomas Faculty of Pharmacy Department of Pharmacy

PHA612 - Laboratory

Experiment 4: Reactions and Analysis of Group I Cations Objectives: At the end of the period, the students are expected to be able to : ● Observe the colors of the products formed in the reactions. ● Develop a systematic method that will identify the ions in an unknown solution through the application of chemical tests.

Table 1: Reactions of the Silver Group Reagents

Ag+ Color and Formula Nature AgCl

4-2 HCl

4-3 NH4OH a. Excess

4-4 NaOH

Ag(NH3)2+ Colorless or Ag(NH3)2Cl

4-5 K2CrO4

White ppt

Ag(NH3)2+ or Ag(NH3)2Cl (silver complex)

Colorless solution

AgOH to Ag2O

White to brown ppt

Pb(OH)2

Whote amorphous ppt

Insoluble

Pb(OH)42or Na2PbO 2

Soluble colorless solution

Brownish red ppt

PbCrO4

Yellow ppt

Insoluble

Na2PbO2

Soluble yellow solution

Canary yellow

PbI2

Yellow ppt

Ag2CrO4

a. NaOH 4-6 KI

Insoluble

AgOH

a. Excess

Ag

Hg 2+ 2

Formula

Color and Nature

Hg2Cl2

White curdy ppt

Soluble aqueous colorless solution of PbCl2

Insoluble

a. Boiling water b. Excess NH4OH

White curdy ppt to gray ppt when exposed to light

Pb+2 Color and Formula Nature White crystalline PbCl2 ppt

Pb(OH)2

White ppt

Insoluble HgNH2Cl & White and black ppt Hg0 HgO ·HNH2NO3

& Hg

Insoluble

White and black ppt Insoluble

Hg2O

Black ppt

Insoluble Hg2CrO4

Orange-red ppt but brownish red on boiling

insoluble Hg2I2

Greenish yellow or green ppt

1

a. Excess Insoluble

Insoluble

HgI4 2- & Hg0 or K2HgI4 & H0

Procedure 4-1 To 1 mL of the unknown solution, add 3M HCl dropwise. Mix thoroughly and centrifuge. Test for completeness of precipitation. Centrifuge and decant the centrifugate. 4-2 Precipitate: AgCl, Hg 2Cl2, PbCl 2 (all white in nature) Add 2 mL boiling water. Centrifuge and decant the centrifugate. 4-3 Solution: PbCl2 4-4 Precipitate: AgCl, Hg2Cl2 Divide the hot filtrate into 3 Add 6M NH 4OH. Centrifuge and decant the centrifugate. 4-5 Precipitate: Black ppt parts: 4-6 Solution: Ag(NH3)2+ a. Add KI solution. Yellow Divide the filtrate into 2 parts: ppt of PbI2, soluble in HgNH2Cl + Hg a. Acidify with 6M HNO3. A turbid solution of hot water to a colorless solution. white ppt of AgCl. b. Add a few drops of KI b. Add dilute H2SO4. White ppt of PbSO4. solution. Pale yellow ppt of AgI. c. Add K2CrO4. Yellow ppt of PbCrO 4. Pb2+ Hg22+ Ag+

2...