Gravimetric and Determination of Nickel Reaction Process Discussion

 I have a few questions regarding the gravimetric determination of nickel, in which the nickel is precipitates as nickel dimethyl glyoxime (so that we can quantify it later on). My two main questions include: #1: Why do we first set the pH to be around 3-4, and then later set it to 8-9? #2: Why do protons emerge in the last equation (as they form the water together with hydroxide)? Where do they come from and why? Which characteristic of the nickel is for this responsible?

 

Hello,

 

I have a few questions regarding the gravimetric determination of nickel. The nickel is precipitated as nickel dimethyl glyoxime through the addition of dimethyl glyoxime C4H6(NOH)2. First a bit acid is added, then a slight excess of aqueous ammonia solution is added. Here is an overview of the procedure, which was used for my theoretical lab protocol:

1.The tested substance is filled to 100ml with water. (The tested substance consists of a nickel salt).

  1. 25 ml of this solution will be taken. 2 ml of HCL (3N) will be added. This will be filled up to 200 ml with water.
  2. Aqueous ammonia is added to set the pH to 3-4.
  3. The solution is heated and 25 ml dimethylglyoxime solution is added while stirring.
  4. With aqueous ammonia (3N) the pH should be set to 8-9.
  5. The solution is stirred for 10 min. A precipitate forms.

 

 

Below are the reactions, which I have written for theis procedure.

word image 412

 

My two main questions include:

 

#1: Why do we first set the pH to be around 34, and then later set it to 8-9?

 

 

#2: Why do protons emerge in the last equation (as they form the water together with hydroxide)? Where do they come from and why? Which characteristic of the nickel is for this responsible?

 

 

 

 

 

 

 

 

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