In the distilled water, I believe that the water is more concentrated in the dish, and therefore the water should transfer from the water to the potato, making the potato bigger in size, and heavier in weight. The potato tissues, being surrounded by a weak solution, will be most likely to swell up and become turgid, taking in all the water it can possibly take in.
So the higher the concentration the more chance of reduction in mass, for example if the concentration is 150g/l the water is more likely to move out. So if the concentration was 0g/l then the mass will in crease because the water has moved in. imp also predicting the same with the length, that the higher the concentration the more chance of seeing the length decreasing. But if the concentration is 0g/l the length will increase in size
Fair Test:
In this experiment on osmosis I will be checking one variable:
1: Different concentration of solution,
To keep this variable the only variable in the experiment I must:
- Keep the potato samples the same length (4cm). This is because if one potato sample is 1cm long and one is 3cm long then the 3cm long sample will have a larger surface area and will osmosis much more quickly. Whilst the one, which is only 1cm, will not allow water to pass throw so quickly.
- Use the same potato. This is because many factors due to the potato may affect the experiment. For example the age and sizes might be different, which means one potato might have more water in them then another.
- Stop the evaporation of any of the salt solution. This is because if the salt solution evaporates past the level of the potato, then the potato sample will have less surface area in the solution so this would make osmosis happen much slower. To stop any solution evaporating a cork lid can be placed on top of the test tube.
- Accurate amount of salt solution: More solution may affect the rate of solution. To make the amount of solution placed in the dish as accurate as possible a measuring cylinder will be used to measure out the exact amount needed.
- Contamination: As each petri dish is filled up with the different salt solutions the measuring cylinder, which would measure the amount of solution, placed in the petri dish may become contaminated with different salt solutions. To stop his from happening, the beaker and syringe must be washed every time they are used.
- Average: To make the experiment as accurate as possible an average will be taken out of the three experiments taken. Also any clearly anomalous results will be ignored.
- Temperature: The temperature may affect the reliability of the experiment for example at extreme temperatures the cells of the potato may die and at less extreme temperatures the experiment may be speeded up. To stop this from happening, all the Petri dish will be kept in the same place and at the same time of the one-hour and half experiment.
Safety procedures:
Safety is an important aspect in this experiment, as you are dealing with sharp knives are salt solutions. This is why I'll be taking this into consideration.
You will be using a very sharp knife, which could injure someone if it’s not handled properly. You should no care it around with the sharp end out. You should also be very careful that the solutions don’t get into our bodies internally, just in case, because you are not fully aware of the damage it could do to you. It would also help if you wear goggle just in case any solutions get on your hand and you try to rub your eyes. You should also be wearing an apron in case any solutions getting to my clothes.
Apparatus:
- Cork Borer,
- Petri Dishes,
- Stop watch,
- Measuring Cylinder,
- Tile,
- Scalpel,
- Potatoes,
- Salt solutions (0g/l – 200g/l),
- Weighing Balance,
- Paper towel,
- Sticky labels,
- Ruler.
Method:
Collect all the apparatus to begin the experiment. First place the cork borer into the potato, fifteen times to give you fifteen single pieces of potato chips. When you have done this, you should singly measure each chip making sure that they’re 4cm long in length. If they are any longer this may alter the readings at the end of the experiment. When cut the potato chips to the right length you should place the chip on the tile, mark of 4cm and cut the chip with a sharp scalpel. The reason you place the chip on the tile is, so that the chip doesn’t become contaminated, with what ever was on the table. Then take a reading of each length of every potato and put it into the results table.
After you had recorded each potato chip, then you should check each chips mass by putting it on the weighing balance. When weighing the weight of the potato chip on the scales, you must not lean on the bench because it affects the weight. You should do this one chip by one chip so that you don’t get the readings mixed up. After you have weighed one chip, put it in the petri dish and label which side you put it on left, centre or right and the solution on the lid using the sticky label. Three potato chips are being placed in each Petri dish so that I can get a better average. There will be five solutions and in every solution there will be three potato chips. Starting the concentration at 0g/l and going up to 200g/l.
When you have five complete Petri dishes labelled then you should add, a different solution to everyone. Each solution should be measured before being poured into the dish. This will make my experiment a fair test. You have to make sure that add enough solution that it is covering each potato chip completely leaving no gaps. As this may alter the readings and give me some poor results
Once this is done time each Petri dish using the stopwatch for an hour and half.
Following after the hour and half open the Petri dish and remove each potato chip carefully and place it on the tile. You Should remove any excess water by rolling the chip on a paper towel, keeping each surface on the towel for 2 seconds, making sure that you do not squeeze the chip so that the results are fair Checks it’s length after you have token it out and record it in the results table. Do this for all the chips. Still making sure that you don’t mix the potato chips up or the solutions they are in. Then you should check each chips mass by placing it on the weighting balance. Take each reading carefully and record it in the results table.
When this is done though the potato chips away and clear your mess up, that you have made. The results table should look half full all you need to do now is to work out the change in mass, the percentage change in mass, the change in length and the percentage change in length. I’m going to repeat this experiment another two times to give me nine results for each solution. At the end of the first experiment you should wash the Petri dishes. This is so that no salt solution is left in them that might change the results.
Results Table:
Temperature Controlled Experiment:
If I could add another variable I would add temperature. For this experiment I will have the same apparatus. From having fifteen potato chips I would have thirty. I would keep fifteen in room temperature and the other fifteen potato chips in the fridge. The temperature of the fridge will be –5 degrees. If the temperature is too cold the cells may die.
This experiment is going to be similar to my pilot study but better. My pilot study that I did in year 10 wasn’t that accurate, so using that information to do this experiment will help me as I will have more knowledge of what i'm doing.
From my pilot study I have chosen to uses some thing form that experiment but to also, do different things. Like to do five different solutions, instead of four. I’m also choosing to have more chips in the temperature experiment. Putting three potato chips in a petri, instead of two. I have also thought of putting a lid on my petri dish because in my pilot study I didn’t. This might of allowed the salt solution to be contaminated. When I didn’t have my lid on my petri dishes the salt solution might of evaporated leaving the potato chip, not completely covered, this might of affected my results.
Having five different solutions instead of four allows me to see if the higher the concentration the more quickly the water moves out the cell. This will make the cell to become flaccid, due to osmosis.
In my pilot study I only used eight potato chips, instead of fifteen. I am using fifteen because this will enable me to get a better set of results and also an average. As in the pilot study I wasn’t able to get an average.
In the pilot study I had only two potato chips per petri dish but in this experiment I’m having three. Having three chips in a petri dish than two will allow me to see how quick osmosis works under controlled temperatures. This will also give me a better average for each solution.
The lengths of the potato chips in the pilot study were only 1.5cm but in the temperature-controlled experiment the length of the chips are 4cm. I had made the lengths longer so that I can see more clearly if the length has changed or not, because on the pilot study there wasn’t a massive change in length.
Pilot Study Results Table:
Method for controlled Temperature:
The method to this experiment is quite similar to the one above.
Collect all the apparatus to begin the experiment. First place the cork borer into the potato, thirty times to give you thirty single pieces of potato chips. When you have done this, you should singly measure each chip making sure that they’re 4cm long in length. If they are any longer this may alter the readings at the end of the experiment. When cut the potato chips to the right length you should place the chip on the tile, mark of 4cm using the knife rather than the pencil because this may, contaminate the, potato chip and cut the chip with a sharp scalpel. The reason you place the chip on the tile is, so that the chip doesn’t become contaminated, with what ever was on the table, last. Then take a reading of each length of every potato and put it into the results table.
After you had recorded each potato chip, then you should check each chips mass by putting it on the weighing balance. When weighing the weight of the potato chip on the scales, you must not lean on the bench because it affects the weight. You should do this one chip by one chip so that you don’t get the readings mixed up. After you have weighed one chip, put it in the petri dish and label which side you put it on left, centre or right and the solution on the lid using the sticky label. Three potato chips are being placed in each Petri dish so that I can get a better average. There will be five solutions and in every solution there will be three potato chips. Starting the concentration at 0g/l and going up to 200g/l.
When you have ten complete Petri dishes labelled then you should add, one solution to two of the dishes than one. So you would have too petri dish, which are the same. Each solution should be measured before being poured into the dish. This will make my experiment a fair test. You have to make sure that add enough solution that it is covering each potato chip completely leaving no gaps. As this may alter the readings and give some poor results. Don’t forget to place the lid back on every petri dish. This will stop the potatoes and salt solution from evaporating or being contaminated.
Once this is done you should place five petri dishes in room temperature, which is about 27 degrees and place the other five dishes in the freezer, which should be about –5 degrees. Time each Petri dish using the stopwatch for an hour and half.
Following after the hour and half remove the five dishes out of the freezer and then open the Petri dish and remove each potato chip carefully and place it on the tile. You should remove any excess water by rolling the chip on a paper towel, keeping each surface on the towel for 2 seconds, making sure that you do not squeeze the chip so that the results are fair. Checks it’s length after you have token it out and record it in the results table. Do this for all the chips. Still making sure that you don’t mix the potato chips up or the solutions they are in. Then you should check each chips mass by placing it on the weighting balance. Take each reading carefully and record it in the results table.
You should have two results table one for the room temperature and one for the dishes in the freezer. The results table is the same as the one above.
When this is done though the potato chips away and clear your mess up, that you have made. The results table should look half full all you need to do now is to work out the change in mass, the percentage change in mass, the change in length and the percentage change in length.
You should repeat this experiment another two times to give you nine results for each solution. At the end of the first experiment you should wash the Petri dishes. This is so that no salt solution is left in them that might change the results or contaminate the next result. Repeating the experiment will help you to get a better set of average results.
