Sorry mith, but that is not necessary. The question as stated does not make much sense: usually experiments that deal with osmosis on plants involve solutes that cannot pass the cell membrane (e.g. sorbitol). When sap cons. = solute cons., no net movement of solvent occurs (no matter what that solute is). In this case, solute is salt. It can increase membrane permeability and cause diffusion of substances from the sap and salt into the sap until new equilibrium is achieved. However, I do not think diffusion will affect osmosis on the whole (I might be wrong though, I never tried to measure osmosis and diffusion at the same time).
it’s an issue of calculating water potential, which is mainly influenced by solute potential in this case. Since solute potential depends on the ionization constant of the solute, it does make a difference what molecules are dissolved. You don’t need to have the same molecules, but when you add up their solute potentials they need to be the same in order to have no net movement.