Expert: Walter Hintz - 2/23/2009

Question
i did this lab i was wondering a 50% sucrose solution is half sucrose and half water. Only the water molecules can pass through the pores of the dialysis membrane, the sucrose molecules are to large. wanted to know how osmosis accounts for the change in mass of the dialysis bags. Also can u give me an explanation in terms of all three types of osmosis keeping in mind with the lab?

Answer
Hi Dan
50% sucrose is half water.  I assume you placed a bag with 50% sucrose in beakers with various concentrations of sucrose.
 Assume beaker 1 is also 50% sugar.  Solution is isotonic and water enters and leaves at the same rate with no change in weight (mass)
 Assume beaker 2 contains 10 % sugar.  solution is hypotonic  H2O leaves bag and mass is less
 Assume bag 3 contains 60% sugar.  Solution is hypertonic  H2O enters bag increasing mass