Mistakes are more easily identified and rectified with the test solution containing all of the cations to be tested than with your unknown which contains all, none, or some combination of the cations. The separation of various cations is accomplished by use of equilibrium principles. In this experiment, the process has been designed to separate and identify each of the four cations. Thus, one should be familiar with the separation process and the identification process. When dealing with an unknown, it is important to both separate and identify.
Careful observations are as important as careful practices.
When the solution is made basic, the distinctive gas, NH3 is evolved. This aqueous gas may be removed from a solution with a gentle application of heat and detected with litmus paper. Place 5 drops of 6 M NaOH in a 100 mm test tube. Add about 10-20 drops of the test solution. Moisten litmus paper with deionized water.