Experiment No. 2 Electrogravimetric Determination of Cobalt, Copper and Nickel from Mixture

Objectives

1. To apply electrogravimetric technique in determining the amount of metal in aqueous solutions of their divalent salts

2. To separate metals from its mixture. Reagents

Conc. H2SO4 conc. HNO3 conc. NH4OH 85% hydrazine hydrate sample CuCl2 and CoCl2 Apparatus

100-mL electrolytic beaker Hot plate Bunsen burner pipet Procedure I. Procedure for Cu in aqueous CuCl2

Place the assigned sample in a 100-mL tall-form (electrolytic) beaker. Slowly add 2.3 mL of conc.

H2SO4. It has to be carefully and slowly to avoid spattering due to overheating. Upon addition of H2S04, brown and white precipitates will be formed with evolution of fumes. Place the mixture in a hotplate and heat it to near boiling or until vapor condensation is observed. Continuously remove the internal condensation by flaming the sides of the beaker with a Bunsen burner. This is done to prevent the return of the chloride to the beaker via reflux. During initial heating the brown and white solids will be dissolved leaving a green solution. The solution will turn pale green after 2 minutes. Add 1 mL of HNO3 while the solution is pale green to remove HCl as azeotrope. Subsequently, the solution turns from pale green to blue green, blue green to light blue and finally to light blue having a white solid. Formation of white solid indicates removal of almost the entire chloride ion. Continue heating for 5 to 10 minutes to assure complete removal of chloride ion. Upon complete removal, dilute the solution with 100 mL distilled water and carry out the electrolysis.

II. Procedure for Co in aqueous CoCl2

Place the assigned sample in a 100-mL tall-form (electrolytic) beaker. Slowly add 4.1 mL of conc. H2SO4. It has to be carefully and slowly as this may result to violent reaction. Fumes will be evolved and the solution will change color from red to blue and blue to purple or blue with pink solid. Place the mixture on a hot plate and het near boiling. Be sure to remove the condensate by continuously flaming the sides of the beaker using Bunsen burner. After heating the mixture will change from light purple solution with a pink solid to a dark, bluer solution with a pink solid. Heat the solution for 10 minutes more or until no more fumes are visible and the boiling appears to have ended. When the entire chloride ion is removed, dilute the mixture with 65 mL distilled water and add 36 mL of conc NH4OH and 0.5 mL of 85% hydrazine hydrate. Heat the solution to 700C and carry out the electrolysis.

Experiment No. 2 ELECTROGRAVIMETRIC DETERMINATION OF

COBALT, COPPER AND NICKEL FROM MIXTURE

Experiment No. 2 Electrogravimetric Determination of Cobalt, Copper and Nickel from Mixture

III. Procedure for Ni in aqueous NiCl2 Place the assigned sample in a 100-mL tall-form (electrolytic) beaker. Slowly add 4.1 mL of conc.

H2SO4. It has to be carefully and slowly as this may result to violent reaction. Fumes will be evolved and a yellow precipitate will form. Place the mixture in a hot plate and heat it to boiling or until the solid changes from yellow to white and then to light green. Be sure to remove the condensate by continuously flaming the sides of the beaker using Bunsen burner. Continue heating for 5 minutes after the indicated color change. When the entire chloride ion is removed, dilute the mixture with 65 mL distilled water and add 35 mL of conc. NH4OH and heat the solution to 700C and carry out the electrolysis.

IV. Separation of Metals

Follow the procedure in preparing aqueous solution of metal samples. Combine the two metal solutions assigned either Cu and Co or Cu and Ni aqueous solutions. Perform electrolysis by varying the current applied. Consult your professor for the value of current to be used.