Calculate the molarities of solutions that contain the following masses of solute in the indicated volumes: (a) 25.8 g of H3AsO4 in 400. mL of solution; (b) 6.33 g of (COOH)2 in 500. mL of solution; (c) 6.33 g of (COOH)2 ? 2H2O in 500. mL of solution.