Aim: To investigate the effect of different concentration of a sugar solution on the amount of osmotic activity between the solution and pear pieces of a given size.
Define osmosis: Osmosis is a net movement of water/ solution molecules from a region of high concentrated area to a region of lower concentrated area through a semi-permeable membrane which lets smaller molecules such as water through but does not allot bigger molecules like glucose to pass through. The molecules will continue to diffuse until the area in which the molecules are found reaches a state of equilibrium (evenly distributed).
Hypothesis: In this investigation, I predict that the lower the concentration of sugar in the solution, the higher the mass of a pear will be. This is because if I place a pear in a high concentration of sugar solution, the water molecules from the pear will diffuse through to a region of high concentration of sugar solution in order to dilute it. The sugar molecules cannot enter the pear as they are bigger molecules so therefore the pear will have a smaller mass. I will also going to use water (neutral) as part of the investigation as I predict that the pear piece will have a heavier mass reason being that the high concentration of water in the beaker travel to a region of a lower concentration of water which is in the pear. In order to find the effect of the osmotic activity that occurred during the experiment, I will first record the mass before the pear pieces were placed in the solution and I will record the pear pieces after the osmotic activity so that I could see the percentage change in mass. I use a variety of sugar concentrations in a solution so that I can pull a relevant data to draw up a decent conclusion. To keep it a fair test, the control variables must not be changed.
In order to keep the investigation fair, I need to have at least 6 control variables and other variables like independent variable which is the data that I need to collect and the other dependent variables. These variables are:
- Size of the pear pieces (2cm)
- Same type of pear
- Volume of sugar solution and distilled water (10cm³/) - Temperature
- Time taken
- Same balance to measure the pear pieces as the measurements may slightly vary between the scales.
Methods of keeping the variables controlled:
I used a borer at a size of 4 in order to cut the pear into similar sizes. In order to make sure that they’re the same, I used a mm ruler (to get a more accurate measurements) and measure the sizes of each pear and all of them have an approximation of 2cm in length. In order to keep the volume of distilled water (I use distilled water as it doesn’t have as much impurities as the tap water) and sugar solutions the same, I used the same measurement cylinder of 20cm³ in order to get a more correct measurement. I also use the pipette so that the volume will be more accurate. I then record the reading at eye level on the meniscus as if I don’t do this, the volume of water won’t be a control variable.
- Different concentration of sugar levels (0.25M, 0.5M, 0.75M, 1M) - Water (0M).
- Mass of the pear pieces after the osmotic activity. (This allows us to see whether if osmosis has taken place and to what extent).
First of all, I cut the pear into 15 identical pieces using the same borer size. I then measure each of the pear pieces using a mm ruler in order to make sure that they all have identical surface areas and lengths and this is a control variable and therefore it must be kept the same. I then place each of the pear pieces on the balance scale and record down their mass in g as my investigation involves with the masses of the pear pieces. After measuring all the pear sizes, I fill in five identical test tubes with 10cm³ of distilled water (0M), and sugar solutions at 0.25M, 0.5M, 0.75M, and...