Chemistry is hard to learn, but so intresting.
Each substance have different behaviour in aqueous solutions. In tha case of Sodium Sulfite, the cationic part of the molecule -sodium- tends to form small quantities of sodium hidroxide, and tends to go up pH slightly (this is the hydrolysis mechanism), and 100 gr/litre and generate a pH 8 approx. solution. In chemistry we think the anionic part of a molecule as less active than the cationic part in water solution.
In Sodium Carbonate, hydrolysis is so strong: may be 1 gr/litre can grouth pH 10 to 11.5. Why? In chemistry we think Carbonate anion as a lot less active in water than the activity of sodium (alkaline hydrolysis so strong).
Here we have a problem to give you the right answer to the original question. In theoretical therms, we can do a few calculations to give the theoretical amounts of PURE sodium carbonate, may be a few milligrams/litre. But, because of the capacity of sodium carbonate to absorb water, you never know exactly how much sodium carbonate and how much water are you weighting. And, may be you don´t use analytical grade of reagents, and you don´t know about purity of your sodium carbonate... I suppose you are not weighting with a 0,0001 g scale and the purity of your Soda, may be is less than ultra pure reagent.
This is not the correct way to correct with some degree of precision the pH of an alkaline solution.
If you want to grow up pH slightly, may be boron compounds may be more accurate to weight and manipulate (Borax or Metaborate, or Boric Acid and Sodium or Potassium Hidroxide).
Each substance have different behaviour in aqueous solutions. In tha case of Sodium Sulfite, the cationic part of the molecule -sodium- tends to form small quantities of sodium hidroxide, and tends to go up pH slightly (this is the hydrolysis mechanism), and 100 gr/litre and generate a pH 8 approx. solution. In chemistry we think the anionic part of a molecule as less active than the cationic part in water solution.
In Sodium Carbonate, hydrolysis is so strong: may be 1 gr/litre can grouth pH 10 to 11.5. Why? In chemistry we think Carbonate anion as a lot less active in water than the activity of sodium (alkaline hydrolysis so strong).
Here we have a problem to give you the right answer to the original question. In theoretical therms, we can do a few calculations to give the theoretical amounts of PURE sodium carbonate, may be a few milligrams/litre. But, because of the capacity of sodium carbonate to absorb water, you never know exactly how much sodium carbonate and how much water are you weighting. And, may be you don´t use analytical grade of reagents, and you don´t know about purity of your sodium carbonate... I suppose you are not weighting with a 0,0001 g scale and the purity of your Soda, may be is less than ultra pure reagent.
This is not the correct way to correct with some degree of precision the pH of an alkaline solution.
If you want to grow up pH slightly, may be boron compounds may be more accurate to weight and manipulate (Borax or Metaborate, or Boric Acid and Sodium or Potassium Hidroxide).