Finding the strength of Soda Ash

 

Scope:

This test method covers the titrimetric determination of the total alkalinity of soda ash. This alkalinity is normally expressed as percent sodium oxide (Na2 O).

Summary of Test Method

Total alkalinity is determined by titration with standard hydrochloric (or sulfuric) acid using methyl orange or modi�?ed methyl orange indicator solution.

Interferences

Alkalies other than soda ash (sodium carbonate) and compounds that consume acid will affect the accuracy of this test method.

Reagents

1 Hydrochloric (or Sulfuric) Acid (1.0 N)—Prepare in accordance with Practice E 200 (record temperature of solution when standardized).

2 Modi�?ed Methyl Orange Indicator Solution or Methyl Orange Indicator Solution—See Practice E 200. 11.3 Water, carbon dioxide-free (freshly boiled and cooled).

Procedure

1. Weigh, to the nearest 0.1 mg, 4.4 +/- 0.1 g (Note 1) of the sample and transfer to a 500-mL conical flask. Add 100 mL of water and swirl to dissolve the sample. Use of the spec�?ed weight of sample requires a 100-mL buret for titration and is recommended. If a 50-mL buret is used, the sample weight should be halved to 2.2 g. Add 3 drops of modi�?ed methyl orange indicator solution

2. Titrate this solution with standard 1.0 N acid to a gray end point.

3. Record the volume to the nearest 0.02 mL and temperature of the acid used. Correct the acid normality for any difference from the standardization temperature by use of the factor DN/°C 5 0.00035 between 20 and 30°C. Add the correction when the temperature of use is below and subtract when above the temperature of standardizatized.

If desired, 0.1 % methyl orange indicator solution may be used.

—The analyst should end the titration at the same shade of color as was used for the end point in the standardization of the acid.

Calculation

Calculate the total alkalinity as percent sodium oxide 

Sodium Oxide Wt% =(A x B X 0.030990) x 100/B

where:
A = acid required for titration of the sample, mL,
B =corrected normality of the acid, and
W = sample used, g.

Alternatively, calculate the alkalinity as sodium carbonate as follows:
sodium carbonate, wt % = 1.7101 x Na2O weight %

If actual sodium carbonate content is desired, the sodium bicarbonate content must be determined separately as:
sodium carbonate (actual), % = A -(B X 0.6308)
where:
A=Na2CO3 , % and
B= NaHCO3, % .

Ref : Courtesy http://en.blijoil.com/UserFiles/Uploads/E359.PDF