Calculate the mass of the precipitate if 25 g of barium chloride and 40 g of sodium sulfate have entered the reaction.

We compose the equation of the ongoing reaction and arrange the coefficients in it:
BaCl2 + Na2SO4 = BaSO4 + 2NaCl.
The precipitate is barium sulfate.
1) Find the amount of barium chloride substance. To do this, divide the mass of the chloride by its molar mass. The molar mass is found according to the periodic table: 25/208 = 0.12 mol.
2) Find the amount of sodium sulfate substance. The calculation is carried out similarly to the first point: 40/142 = 0.28 mol.
Lack of sodium sulfate. The calculation is carried out on it.
3) One mole of sodium sulfate accounts for one mole of barium sulfate. This means that the amount of barium sulfate substance is 0.12 mol.
4) Sludge mass: 0.12 * 233 = 27.96 g – answer.