Water Potential: Lab Write Up

Topics: Concentration, Solution, Solutions Pages: 3 (855 words) Published: May 2, 2012
Water potential is the measure of free energy of water in a solution. The purpose of this lab was to find the water potential of a potato cell. The problem of this lab was, if there was a high molarity of solute, would it have a positive or negative water potential? The hypothesis of the experiment was, if there is a high molarity of solute then the water potential would be lower or negative. After obtaining potatoes, we cut them into pieces, weighed them, and then placed them in a solution overnight. In this lab, we explored the potato cell’s water potentiality. From the results, we found that it the higher the molarity of a solution is, the lower the water potential of the potato cell. This finding supports our hypothesis.

Water will always move from an area of high water potential to an area of low water potential. Water potential is the measure of free energy of water in a solution. Water potential is represented by the symbol ψ (psi). Water potential is affected by two physical factors. One of factor is the addition on solute (ψs); addition of solutes to a concentration will lower the water potential of that solute, causing water to move into the area. The other factor is pressure potential (ψp). An increase of pressure potential raises the water potential. Water movement is directly proportionate to the pressure potential. The equation for water potential is: ψ = ψp + ψs

The water potential of pure water at atmospheric pressure is defined as being zero. The water potential value can be either positive, zero or negative. An increase in pressure potential results in a more positive value, and a decrease in pressure potential results in a more negative value. In contrast to pressure potential, solute potential is always negative; since pure water has a water potential of zero, any solutes will make the solution have lower or negative water potential. In general, an increase in solute potential makes the water potential value...
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