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How Does The Concentration of a solution affect the rate of osmosis Osmosis can be defined as the net movement of water molecules from high to low concentration through a semi-permeable membrane. When a substance such as sugar and salt (which we will be using in the experiment being analysed) dissolves in water it attracts water molecules to itself and through that it stops them from moving freely. During osmosis in a plant cell, the water particles move through the cell membrane and into the large vacuole, where they are stored in a solution of sugars and salts. For this experiment, I will be using sucrose( and distilled water), which has large particles that cannot fit through the holes in the selectively permeable cell membrane, but water particles can fit through, as they are much smaller. Before I start thinking about what I am going to test in my experiment and how I am going to carry it out, I have to know the range of factors that might influence these choices. I therefore have to identify and concentrate on the most important factor: Temperature affect osmosis, because the greater the temperature the greater the energy (heat), the faster the molecules under the influence of the heat will move and the faster they will diffuse across the membrane. This isn't the only problem because heat can affect this experiment physically as well. There is a possibility that the cell membranes will be denatured by heat and behave differently towards the experiment. The water molecules in the solution and in the potatoes might also evaporate which is uncontrollable. Furthermore, the type of cell is also very vital in osmosis because of the fact that the permeability of the membrane and the surface area of the membrane can be different in potatoes of exactly the same type, even from the same region. If the membranes of potato I use in the experiment have different levels of permeability, water will flow more easily through some than others, changing the rate of osmosis. ...read more.


* Although I am not controlling the temperatures at which osmosis takes place, I am going to measure the temperature of all of the solutions so that if there are any anomalies, they may be due to a change in temperature. Higher temperatures would increase the rate of reaction as particles have more energy to move faster, and so loses or gains more water than other potatoes. * I am going to place the potato cylinders on paper towels after they have been in the boiling tubes to soak up any excess water which may be on the outside of them and add to the mass. Safety Precautions To ensure my classmates and my own safety I will always wear safety goggles while partaking in the experiment especially near dangerous and harmful materials. I will always obey the laboratory rules and be careful when using sharp tools like scalpels, knives etc. and will use the tongs when handling hot materials. I will keep all my apparatus away from the edge of the working area as they may be accidentally spilt. After I finish using the apparatus I will put it all away and clean my working area. Main Experiment Solution Concentration (Moles) Potato Mass (Grams) Test 1 Test 2 Test 3 Average Mass After Experiment Before After Difference Before After Difference Before After Difference 0.1 2.5 2.7 +0.2 2.5 2.8 +0.3 2.5 2.6 +0.1 2.7 0.2 2.5 2.7 +0.2 2.5 2.6 +0.1 2.5 2.7 +0.2 2.67 0.3 2.5 2.4 -0.1 2.5 2.5 0 2.5 2.6 +0.1 2.5 0.4 2.5 2.5 0 2.5 2.4 -0.1 2.5 2.4 -0.1 2.43 0.5 2.4 2.4 0 2.4 2.4 0 2.4 2.4 0 2.4 0.6 2.4 2.5 +0.1 2.5 2.5 0 2.6 2.5 -0.1 2.5 0.7 2.5 2.3 -0.2 2.5 2.6 +0.1 2.5 2.4 -0.1 2.4 0.8 2.6 2.4 -0.2 2.5 2.5 0 2.6 2.5 -0.1 2.43 0.9 2.5 2.4 -0.1 2.6 2.4 -0.2 2.5 2.3 -0.2 2.43 1 2.5 2.4 -0.1 2.4 2.5 +0.1 2.4 2.4 0 2.47 Rhys' Results Solution Concentration (Moles) ...read more.


There's not much that can be done in order to avoid this as it is impossible for me to be able to get samples that contain all of the same cells within them. However, in order to ensure that the cells are as similar as possible, I will take samples from the same part of the same potato. The sucrose solutions may not have been shaken properly. This would mean that the molarity within the sucrose solutions in the boiling tubes would not have been the same throughout the solution. Therefore the water potential of parts of the solution could have been greater than or lower than the samples within the boiling tube. This would mean that the mass readings after the experiment would have been completely incorrect as the three samples in each boiling tube may not have been in the same environments. To avoid this happening, I need to ensure that all of the solutions are thoroughly mixed together by shaking the boiling tubes with bungs in them. The potato samples were not all left in the distilled water for exactly the same amount of time, especially as all of the samples and repeats were done at the same time. So, I was not able to put in/take them all out of the solutions at the same time. This would have affected my results as some of the samples would have been left in the solutions for longer and so osmosis would have had longer to occur in these samples. Meaning that the change in mass for these samples would be greater than if they had been left in for as long as the other samples. To avoid this happening, I could do each sample and its' repeat separately as well as using a stop clock in order to ensure that all of the samples and repeats are left in the solutions for the same amount of time. ...read more.

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