how many grams are in a 438mL of a 0.650M Na2SO4 solution

i did 438 divided by 1000 to get .438. then I calculated the molar mass of 142.05. I divided .650 divided by 2 to get .325. I then multiplied the number of moles by 142.05 and got 20.2 grams but I don't know where I went wrong