GRAVIMETRIC DETERMINATION OF NICKEL IN NICKEL ORE

OBJECTIVES:

1. The student will dissolve an ore sample using nitric acid.

2. The student will use sintered glass filtering crucibles.

3. The student will use the technique of getting items to constant weight.

4. The student will chemically precipitate the nickel in an ore.

PROCEDURE: The steps to dissolve the sample take 4 to 5 hours. Treat the samples for both the gravimetric and EDTA titration together! While doing the sample dissolution also get your crucibles to constant weight.

Weigh 0.5 gram samples of dry unknown into a 400-ml beaker. Cover and add 20 ml. of 15 M nitric acid. Warm gently then boil until red fumes no longer come off (UNDER THE HOOD), all black particles should be dissolved and the volume should be about 5 ml. If not, add 5 ml. of 12 M HCl and heat for a few minutes under the hood. Cool and add 20 ml. 12 M HCL. Take to dryness, add 10 ml. hydrochloric acid (12 M) and again take to dryness. Bake at 110o for one hour. Cool, add 10 ml. 12 M HCl, heat easily a few seconds, dilute with 100 m. of hot water and set on a hot plate for 15 minutes.

Filter through a fine qualitative paper into 400 ml. beakers, wash well with hot water and proceed with analysis. Add 10 ml. 20% ammonium chloride solution, add 20 ml. 10% tartaric acid, dilute to 200 ml., heat to nearly boiling, cautiously add ammonium hydroxide (1:1) from a buret until the solution is slightly alkaline. Take back to feebly acid by addition of a few ml. HCl. The reason the precipitation is from acid solution is that a more easily filterable precipitate will result. The changes in color will indicate the acidity to alkalinity of the solution, but this should be checked against a sensitive indicator paper (not litmus). If iron hydroxide appears when the solution is made alkaline, insufficient tartaric acid is present.

Add 15 ml. of 1% solution (alcoholic) of dimethylglyoxime drop-wise. (A buret is an easy way to do this.) Add 1:1 ammonium hydroxide until the solution is just alkaline (do NOT use litmus) then add 2 or 3 drops in excess. (A buret is a convenient method for the addition of ammonium hydroxide.) A dense red ppt. should form. Stir vigorously. Place on a hot plate for 15-20 minutes, stir occasionally, finally check alkalinity and filter through a constant weight sintered glass crucible. Wash well with hot water containing 2 or 3 drops of ammonium hydroxide. Dry at 110o - 120o C for 2 hours. Weigh as C8H14H4O4Ni containing 20.32% Ni.

TO GET AN ITEM TO CONSTANT WEIGHT: Constant weight is defined as that state when a substance will not change its weight on heating. This is achieved by heating the object. Weighing the cooled object and then heating again, cooling again, and weighing a second time. If the two weights agree within 0.5 mg., the object is said to be at constant weight. If not then the heating, cooling and weighing process is continued until two successive weighings do agree within 0.5 mg. Use the final weight in the calculations.

CALCULATION: Calculate percent nickel in sample. Include a computer printout for the calculations.

SAFETY AND DISPOSAL INFORMATION: Dispose of all wash solutions in the " Grav Ni WASTE" container. All crucibles should be washed in 6 M HCl.

CAUTION: Remember to treat all chemicals with respect.

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