30. Solving a chemistry problem

11. A sample of fermented rye dough (m=25 g) was homogenized in 250 cm3 of water. The filtered aqueous extract (20 cm3) was titrated with 0.1000 mol/dm3 NaOH solution in a cell with a glass electrode and a saturated silver chloride reference electrode. The following data were obtained near the stoichiometric point:
V(NaOH), ml: 0.60; 0.70; 0.80; 0.90.
pH: 7.50; 7.62; 8.35; 8.57.
Calculate the mass of acids (g per 100g of dough) in terms of lactic acid.