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1 Osmosis and the van't Hoff i factor Osmotic pressure is the pressure that arises whenever two solutions with differing concentrations of particles...
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Osmosis and the van't Hoff i factor lab question.If you performed this experiment using MgCl22

as the solute would the molar concentration of MgCl that is isotonic to the potato be higher, the same or lower than the molar concentration of NaCl that is isotonic to the potato? Explain.

1 Osmosis and the van't Hoff i factor Osmotic pressure is the pressure that arises whenever two solutions with differing concentrations of particles are separated by a semipermeable membrane, (one that lets solvent pass through but not solute). In an attempt to have the two concentrations become equal, solvent will migrate from the compartment with lesser concentration to the one with larger concentration. The osmotic pressure is the pressure needed to prevent this migration from occurring. The cells in living things have semipermeable membranes. When cells are placed in contact with a solution of a higher concentration of particles than in their interior, (a hypertonic solution), water flows out from the cells and they decrease in mass. If the cells are placed in contact with a solution with a lower concentration of particles, (a hypotonic solution), water flows into the cells and they increase in mass. If the solution and cells have the same concentrations of particles (isotonic) no migration of water occurs and the mass remains constant. In our experiment we will be using a collection of living cells known as a potato. Small, weighed pieces of potato are placed in solutions of differing concentrations of particles. After about 45 minutes, the pieces are removed and reweighed. By determining the mass change of the potato pieces, we can determine whether the solutions are hypotonic, isotonic, or hypertonic. In practice it is difficult to find the exact solution that is isotonic, so a graph can be drawn plotting the fractional mass change vs. molarity of solution. The molarity corresponding to the point where this line crosses the x-axis is the molarity of the solution that is isotonic to the potato.
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2 In our experiment we will be using glucose and NaCl as solutes. Glucose is a non- electrolyte, so one mole of glucose yields one mole of particles in solution. NaCl is an electrolyte and in an ideal situation, one mole of NaCl should yield 2 moles of particles: NaCl (s) Na + (aq) + Cl - (aq). However, since these aqueated ions have opposite charges, they do attract each other somewhat and do not act as truly independent particles in solution. The van't Hoff factor, i , measures the extent to which an ionic compound effectively produces independent particles. solute mole particles of moles effective i In very dilute solutions of NaCl, where the ions are well separated from each other, the i factor approaches 2.00. In more concentrated solutions, where interionic attractions become significant, the i factor can be as low as 1.8. If we know the concentration of particles in a solution of the non-electrolyte glucose that is isotonic with the potato, we know that this must be equal to the concentration of particles in a NaCl solution that is also isotonic to the same potato. Since we know the molarity of particles in this solution, we can calculate the van't Hoff factor for NaCl. L / NaCl mole L / particles of moles i For example, if a 0.25 M solution of glucose and a 0.14 M NaCl solution are both isotonic with the same potato, they must both contain 0.25 moles of particles per liter. The i factor for NaCl at this concentration is NaCl mol particles/ moles 1.8 L / NaCl mol 0.14 L / particles mol 0.25 i Half of the class will work with glucose and the other half with NaCl and determine what concentration of each solute is isotonic with a piece of the same potato. The results of the entire class will then be combined to find the value of i.
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