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Osmosis Coursework. Investigation Of The Effect of Different Concentrations of Sucrose Solution on Potato Strips

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Introduction

Investigation Of The Effect of Different Concentrations of Sucrose Solution on Potato Strips Aim of Investigation I aim to investigate if osmosis occurs when potato cylinders are placed in different concentrations of sucrose solution. I will weigh the potato cylinders at the start and then again after three hours to find the percentage change in mass in each different solution. I will plot a graph of my results and from the graph I hope to find the internal sucrose concentration of the potato. This point is where there is no percentage change in mass as the internal and external sucrose concentrations will be equal and therefore there is no concentration gradient. Scientific Knowledge Osmosis is defined as 'the movement of water molecules from an area of high water concentration to an area of low water concentration, across a selectively permeable membrane' (Collins 1999). Osmosis is a special type of diffusion, in which water molecules move through a selectively permeable membrane. Because water are small molecules and are able to fit through the gaps in the membrane. The large polar molecules (e.g. Sugar) cannot fit through the small gaps of the membrane, this is what makes it semi-permeable. When the concentration of water molecules is high and the concentration of the solute molecules is low, this is called a weak / dilute /hypotonic solution. ...read more.

Middle

- Find the change in mass of the potato cylinder, record results and finally work out the percentage change. Strategy Of Dealing With Results I will collect and record my results in a table as shown below. Table Showing Change In Mass Of Potato Tissue In Different Molar Solutions Molarity of Sucrose Solution (M) Original Mass (g) Final Mass (g) Change in Mass (g) % Change in Mass Average % Change in Mass Rack 1 2 3 1 2 3 1 2 3 1 2 3 - 0 0.1 0.3 0.5 0.7 To find the percentage change in mass I will use the formula I will then present my results on a graph: Relationship Between Change in Mass of Potato Tissue in different Molar Sucrose Solutions Description Of Results My results did not all lie on a straight line so I drew a line of best fit which passed through two of my points and close to the rest of my points, except for one slightly anomalous result at 0.4M. The line of best fit slopes downwards, we can see from the graph as the concentration of the solution increases, the percentage change in mass decreases (in a 0M solution the average % increase is 16.1 and as the Molarity of the solution increases to 5M the average percentage change in mass decreases to negative 17.4). ...read more.

Conclusion

But the following may have been sources of inaccuracy. 1) When blot drying the potato tissues some potato tissues could have been dryed more than others, to try to eliminate this to the best of my ability I rolled the potato tissue gently along a piece of tissue exerting as little as possible force 2) Inaccurate cutting(not same length / surface area), to eliminate this I used the average percentage change in mass of the potato tissue 3) In accurate molarity of sucrose solutions There were a few possible sources of error in my investigation. One main error that occurred would have been not drying each potato cylinder to the same extent each time, as pushing on the cylinder would have take out more water. If I had the opportunity to repeat the experiment I would have improved it by carrying out a fourth or fifth investigation, and for each experiment have investigated a wider range of external solutions (e.g. 0.15M) having more points of the graph would have allowed me to have a more accurate line of best fit and therefore would help me to find the isotonic molarity. I also could have cut the cylinders into small pieces which would increase their surface area, giving a better opportunity for different concentrations of sucrose solutions to work on the potato strips. To make sure my results where fair a compared them with the class result. ...read more.

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