Separation of cations into groups on the semimicro scale

9 SEPARATION OF CATIONS INTO GROUPS ON THE SEMIMICRO SCALE Once a solution is produced, the systematic search for cations can be started. As the first step, cations should be separated into groups later separations within the individual groups must be carried out. When making these separations, the results of preliminary tests must always be kept in mind. If we know for sure that certain cations are present or absent, we can make appropriate simplifications in our separation procedures, which will result in considerable gain of time. 

Separation of cations into groups can be carried out according to the instructions of Table VI. 11. Note, that this method is suitable only if anions of organic acids, borate, fluoride, silicate, and phosphate are absent. Modifications of the separation scheme in the presence of these anions are described in Section VI. 17. 

The ppt. may contain PbCl2-white. Hg2Cl2 -white. AgCl -white. Group 1 (silver group) present. Examine by Group Separation Table VI. 12 (Section VI.10) 

This must not give a ppt. with 1 drop of dilute HC1. Add 4 drops of 3 % H202 solution (4), and heat on a water bath for 2-3 minutes. Adjust the HC1 concentration to about 0-3m (5). Pass H2S through the warm solution until precipitation is complete (6). Centrifuge and wash (7). 

PbS-black. Bi2S3 -black or dark-brown. CuS-black. CdS - 

---

Table VI.ll Separation of cations into Groups on the semimicro scale (anions of organic adds, borate, fluoride, silicate, and phosphate being absent) Add 2 drops (1) of dilute HC1 to 1 ml of the clear solution in a 3 ml centrifuge tube (or a 4 ml test-tube). If a ppt. forms, stir and add a further 1-2 drops to ensure complete precipitation. Centrifuge (2) wash the ppt. with a few drops of cold water (3) and add washings to centrifugate.

---