Before hydrazine came in to use to remove dissolved oxygen in the water steam boilers, Na2SO3 was usually used for this purpose:
2Na2SO3(aq) + O2(aq) -> 2Na2SO4(aq) define what mass of Na2SO3 is needed to remove O2 from 3x104L of water?
O2 dissolves in water to the extent of 0.0044g in 100mL of water at 20C