A method to manufacture bags containing bicarbonate powder, each bag having two pockets (2, 3) communicating by means of a lower U-shaped channel (5), the bottoms (6, 7) of the pockets and the outer side (20) of the lower channel (5) defining the bottom of the bag (1). The method comprises the steps of longitudinally folding a plastic film, welding the folded film so as to form a semifinished product (31) comprising a succession of open bags, with the relative pockets (2, 3) arranged transverse to the folding line (32), cutting the semifinished product (31) so as to separate the open bags, and filling the pockets (2, 3) of each open bag with bicarbonate powder. Forming the semifinished product (31) comprises the steps of performing, along the folding line (32), a succession of first welds shaped as the bottom of the bags and performing a succession of second welds (13), which are transverse to the folding line (32), so as to divide the pockets (2, 3) of each pair of pockets (2, 3) from one another and to define the inner side (14) of the lower channel (5).
