Give the procedure for sampling metals and alloys
Answers
Procedure :
1. Place a small piece of brass in a china dish and heat this with minimum quantity of 50% HNO3 so as to dissolve the piece completely.
2. Continue heating the solution till a dry solid residue is obtained.
3. Dissolve the solid residue in dil. HCl and filter. Add distilled water to the filtrate.
4. Pass H2S gas through the filtrate. A black precipitate of copper sulphide is obtained. Separate the black ppt. and keep the filtrate for the test of Zn+2 ions Dissolve black ppt. by heating them with 50% HNO3. To this solution add ammonium hydroxide solution. Appearance of deep blue colouration in the solution shows the presence of copper ions in the solution.
5. To test Zn+2 ions, boil the filtrate to remove H2S gas, then add solid NH4Cl to this and heat to dissolve NH4Cl. Add excess of NH4OH so that a solution is ammoniacal. Now pass H2S gas through this ammoniacal solution. Dirty white or grey precipitation indicate zinc. Separate the precipitates and dissolve it in minimum amount of dil. HCl. Boil to expel H2S gas and add potassium Ferro cyanide solution, white or bluish white ppt. confirm Zn+2 ions in the solution.