SOP: Determination of Alkalinity in Salt

GIFSQ — Global Institute for Food Safety & Quality

Principle

The alkalinity of the salt, expressed as sodium carbonate, is determined by titrating an aliquot of the water-insoluble-matter filtrate against standard hydrochloric acid with methyl orange as the indicator.

Apparatus required

• Burette (for the hydrochloric acid titration)

Reagents

a. 0.1 N hydrochloric acid, HCl, standard solution.

b. Methyl orange indicator.

Sample preparation

Use 100 ml of the filtrate obtained from the determination of water-insoluble matter.

Procedure

To 100 ml of the filtrate obtained from the determination of water-insoluble matter, add a few drops of methyl orange indicator

↓

Titrate against 0.1 N HCl; note the titre

Calculation

                      Titre × N of HCl × 53 × 100

% Alkalinity as Na₂CO₃ = ——————————————–
Weight of salt in 100 ml of filtrate (g) × 1000

Where,

• Titre = ml of HCl used in the titration
• N of HCl = normality of the hydrochloric acid
• 53 = equivalent weight of Na₂CO₃, as printed
• Weight of salt in 100 ml of filtrate (g) = weight of salt contained in 100 ml of the filtrate

Note: the book’s printed formula line is partly garbled in the extraction (“WeSF salt”); the formula above follows the printed variables in the standard form.

Precautions

• Use the filtrate from the water-insoluble matter determination for this titration.
• Take the methyl orange end point exactly.

References

Ranganna, S., Handbook of Analysis and Quality Control for Fruit and Vegetable Products, 2nd edition.