Sodium carbonate (E500i)

No. Sodium carbonate (E500i) is not one of the markers Open Food Facts uses to classify a food as processed or ultra-processed, so on its own it doesn't raise a product's NOVA group.

What it is

Stabilisers are substances which make it possible to maintain the physico-chemical state of a foodstuff; stabilisers include substances which enable the maintenance of a homogenous dispersion of two or more immiscible substances in a foodstuff, substances which stabilise, retain or intensify an existing colour of a foodstuff and substances which increase the binding capacity of the food, including the formation of cross-links between proteins enabling the binding of food pieces into re-constituted food.

A product that contains it can still be ultra-processed for other reasons: 147 of the 163 products here that contain sodium carbonate (E500i) (90%) are in group 4 because of other ingredients or additives.

Function

Stabiliser: Stabilisers are substances which make it possible to maintain the physico-chemical state of a foodstuff; stabilisers include substances which enable the maintenance of a homogenous dispersion of two or more immiscible substances in a foodstuff, substances which stabilise, retain or intensify an existing colour of a foodstuff and substances which increase the binding capacity of the food, including the formation of cross-links between proteins enabling the binding of food pieces into re-constituted food.
Thickener: Thickeners are substances which increase the viscosity of a foodstuff.

Functional class definitions from the EU food additives regulation, via Open Food Facts.

More about sodium carbonate (E500i) on Wikidata