Osmosis

A Study of Osmosis: Determining the Solute Concentration of Potatoes. The purpose of this lab is to discover the effect of various solute concentrations undergoing osmosis in potato sections. Abstract: Osmosis is the movement of water particles across a selectively permeable membrane from an area of high concentration to an area with low concentration. Osmosis occurs when a semi/partially permeable membrane allows miniscule water particles to pass in or out towards a low water concentration. To achieve an equivalent osmotic potential, the concentration of water molecules have to be equal on either side of the partially permeable membrane, this will result in a constant mass. The theory is that water molecules are in constant motion. Since the water molecules are constantly vibrating they strike the membrane and create water potential. Solutions with a low water potential have a high solute potential, known as a hypertonic solution. Solutions with a high water potential have a low solute potential, known as a hypotonic solution. Molecules of water move by osmosis until the concentration of water molecules is the same on each side of the partially permeable membrane. If this is achieved, we now have an isotonic solution (equivalent osmotic potential). Hypothesis: We predict that as the solute concentration (mol.L-1) increases the mass of the potato will decrease. The reason for this is because water particles move from a high concentration to a low concentration. As the solute concentration gets higher, the water concentration will get lower, and as a result the water particles will move out of the potato and in to the solution outside because the concentration outside the potato is lower. Hence, the higher the solute concentration the more mass the potato will lose. Materials: • Test tubes • 10-mL graduated cylinder • 2 100mLbeakers • 10-mL, 5-mL, 2-mL pipette • Test tube rack • #5 cork borer • Single-edged razor blade or scalpel and handle • Ruler • Centigram balance/electronic balance • Potato • 1 mol-L -1 • Distilled water • Marker for test tubes • Grid paper • Paper towels Procedure: 1. Prepare seven test tubes each with a different solute concentration by using a pipette and adding the correct amount of water and sucrose. 2. Using a #5 borer to bore a section of potato. Cut the skin off both ends and then use a razor blade to trim the section to a length of 4cm. Rinse the sections with distilled water and blot them dry with paper towel. 3. Use a balance to determine the mass of each potato section. Record the mass to the corresponding test tube location on the chart. 4. After 24 hours, remove each potato section and gently blot dry. Record the final mass of each potato section. Safety precautions: CAUTION: Work carefully with sharp instruments.