Measuring the Rate of Osmosis Using - Lab Report Example

Introduction: Osmosis A solute is a substance that is dissolved in a solution. A solution is a homogeneous, liquid mixture of two or more substances.A Solvent is the dissolving agent of a solution. Water is the most versatile solvent known. This dispersal of molecules is called diffusion and is defined as the net movement of molecules from an area of high concentration to an area of low concentration. The rate of this movement can be affected by: 1. The steepness of the concentration gradient between the two materials. 2. The molecular weight of the molecules. 3. The temperature and pressure of the substances. Diffusion can occur across membranes if the membrane has a molecular structure to allow the molecules of the diffusing substance to pass through it. The membrane is said to be permeable to the diffusing substance. Some membranes may have a molecular structure such that certain substances can diffuse through them but other substances cannot. Such membranes are called selectively permeable membranes. The ability of a molecule to pass through a membrane is dependent on its molecular size and structure. The movement of many materials into, out of, and throughout living cells is often by simple diffusion. A special kind of diffusion is the phenomenon known as osmosis. Simply defined in biological systems, osmosis is the diffusion of water through a selectively permeable membrane from a region in which it is highly concentrated to a region in which its concentration is lower. Since all cells contain molecules in solution (known as solutes) that cannot pass through the membrane, osmosis always occurs when cells are placed in dilute or concentrated aqueous solutions. When comparing solutions, the term “tonicity” is used. Tonicity is defined as the relative amount of solutes in a solution when compared to another solution. A solution with a higher concentration of solutes is said to be hypertonic, while a solution with a lower concentration of solutes is said to be hypotonic. If two solutions contain equal concentrations of solutes they are said to be isotonic. Observations: Table I: Weight Change of Eggs (g) vs Time (minutes) Time (Min) 0% sucrose 10%sucrose 20% sucrose 30% sucrose 40% sucrose Unknown 0 96.1 102.9 87.32 96.79 96.33 101.73 15 95.2 103.3 86.36 99.97 93.66 102.6 30 97.4 103.4 85.76 93.67 91.85 103.24 45 100.3 103.5 85.17 92.45 90.2 103.74 60 101.1 103.6 84.45 91.73 89.24 103.96 75 106.57 103.6 84.37 90.8 88.27 104.12 Thus it can be observed from the chart that 0% Sucrose solution was hypotonic with respect to the egg as it initially weighed less and as time passed its weight increased. Thus some molecules of the sucrose solution diffused into the deshelled egg membrane with relatively lesser concentration by osmosis to neutralize the concentration gradient. On the other hand, it can be observed from the graph that the solution with 30% sucrose solution was hypertonic with respect to the egg. This is because initially the egg weighed more and as time passed its weight decreased. Thus some solute particles diffused from the egg into the surrounding 0% sucrose solution of lesser concentration by osmosis. Table II: Weight Change of Eggs (g) vs Time (minutes) Time (Min) 0% sucrose 10%sucrose 20% sucrose 30% sucrose 40% sucrose Unknown 0 0 0 0 0 0 0 15 0.9 -0.4 0.96 1.82 2.67 -0.87 30 -1.3 -0.5 1.56 3.12 4.48 -1.51 45 -4.2 -0.6 2.15 4.34 6.13 -2.01 60 -5 -0.7 2.67 5.06 7.09 -2.23 75 -10.97 -0.7 2.95 5.99 8.06 -2.39 a. What conclusion can you draw from the data in this graph? Ans a. From the graph, we can conclude that 0% sucrose solution was extremely hypotonic with respect to the egg. This is because the change in weight in the 0% solution egg is most pronounced. This indicates that there was a steeper concentration gradient between the deshelled egg inner environment and the outer sucrose solution and it took longer to come to similar concentration The concentration gradient between the remaining sucrose solutions and the internal egg environments were less steep. Solution with 40% sucrose was extremely hypertonic with respect to the deshelled egg. This is because its weight increased linearly at almost all time intervals. This suggests that molecules from the sucrose solution diffused into the egg by osmosis thus increasing its weight accordingly. The solution with unknown concentration of sucrose is positioned between the 0% and 10 % sucrose concentration curves. Thus its concentration is expected to be around the same range. b. Which solutions were hypotonic? Hypertonic? Isotonic? Ans b: Solution Sucrose Concentration Hypotonic 0%, Unknown Hypertonic 20%, 30%, 40% Isotonic 10% Table III: Total Weight Change of Eggs (g) vs Sucrose Concentration (%) Time (Min) 0% sucrose 10% sucrose 20% sucrose 30% sucrose 40% sucrose Unknown Total Weight Change -10.47 -0.7 2.95 5.99 8.06 -2.39 Q. 1 Determine the isotonic point of the contents of a chicken egg. From the graph trendline, we get the equation of the graph as: y = 43.75x - 7.584 At the isotonic point, y i.e Total weight change will be 0. Thus substituting in the equation: 0= 43.75x - 7.584 43.75x= 7.584 X= 7.584/43.75 X= 0.1733 Thus the isotonic point is at 17.33% Q2. Determine the concentration of the unknown solution. From the graph trendline, we get the equation of the graph as: y = 43.75x - 7.584 The total weight change for the Unknown concentration solution i.e the value of y= -2.39 Thus, -2.39 = 43.75x – 7.584 43.5x= 5.194 X= 5.194/43.5 X= 0.1194 Thus Unknown concentration of sucrose solution is 11.94% It is hence important to understand the concept of osmosis and practically demonstrate it along with analytical graphs, observations and results. We encounter the phenomenon of osmosis quite frequently in day to day life: Examples: Feeling excessively thirsty in summers or in desert like dry solutions or whenever we consume too much of dry food like biscuit is the body’s response to the environment to balance for body fluids. Salt curing of meat in brine is another example of osmosis. In plants osmosis is at least partially responsible for the absorption of soil water by root hairs and for the elevation of the liquid to the leaves of the plant. However, plants wilt when watered with saltwater or treated with too much fertilizer, since the soil around their roots then becomes hypertonic. Freshwater and saltwater aquarium fish placed in water of a different salinity than that they are adapted to will die quickly, and in the case of saltwater fish, dramatically. Read More