Planning Experimental Procedures - Osmosis Experiment.

OSMOSIS EXPERIMENT

Planning Experimental Procedures

It is known that liquids move from a low concentrated area to a higher concentration. This is more commonly known as osmosis. The liquids try to balance out the concentration. Osmosis occurs commonly in cells. Substances such as water are diffused into the cell until the concentration from the outside and inside of the cell are as equal as possible.

The aim of the investigation is to see if increasing the surface of a potato tube will affect how fast the process of osmosis takes place for the movement of water in or out of the potato.

The apparatus and resources that are going to be needed to go through with this experiment is: distilled water, Electric scales, Potato, cork borer, knife, Measuring cylinder, test tubes,

I first had to get a potato. I than used a cork borer to cut out about six potato cylinders. For safety, i did not hold the potato in my hand while cutting out the cylinder but left it on the desk. Each cylinder had to be the same size and because we got a small potato i cut out six cylinders at the length of 3cm long, they all had to be 3cm long otherwise it would not have been a fair test. Not every cylinder came out 3cm long and so we had to use a knife to cut it down to size, care was taken whilst using the knives. i than weighed each potato cylinder and recorded the results that we got. Next, i took six test tubes filled with 25ml of distilled water. In the first one i put a whole potato cylinder in the test-tube, in the second i cut the potato cylinder into two, and for the next I cut it into four, six, eight and the last we cut into ten, we than left it in their for a long period of time. When I return to them I will dry of the potato samples making sure they stay in order. I will then re-weigh the potato samples and record these results. After doing this I will find out how much the weight has changed and by what percentage, by using the following method:

% Increase in mass = increase in mass × 100.

I will then try to link this with the explanation of osmosis to see if there is a link between more surface area and increase in overall weight after a day.

This experiment was repeated another two times, to make the experiment a fairer test.

To make the experiment safe, all I can do is carrying out the obvious. This includes tucking in stools and placing bags under desks. I must stand when doing the experiment and never run for any reason, laying paper towels, don’t rush anything, and handle equipment and apparatus carefully.

I predict that the more pieces there are the more water the potato will take in. I think this because by cutting something you are increasing the surface area, and by increasing surface area of the potato, there are more places that water can enter the potato. If the concentration of the cell is higher than the surrounding liquid, water, will pass through the cell membrane into the cell until the concentration is equal as possible. In this case the cell may increase in size and therefore weight. The speed of this process will depend on the surface area of the potato exposed to the surrounding liquid.

I predict that if I double the surface area exposed in water, then the speed of osmosis will also double. This means the potato will increase in weight faster because water tries to enter its cells and dilute the sugar content inside.

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To make a fair test some simple procedures will have to be done. I will have to make sure that all the potato tubes are the same size and that I put the same amount of liquid in the beakers I will also have to keep at the beakers in the same place so that temperature and light does not affect the results I would be recording. To make the measuring of the potato tubes accurate I will use an electric scale to two decimal places. This would give me accurate readings. I will keep all the potatoes in the beakers for the same amount of time or this would clearly affect the results because some tubes of potato would have more time to gain mass. I will also repeat the experiment and even compare my results with other people to ensure my results are as fair as possible.

Obtaining Evidence

Once we cut the potatoes and put them in separate test tubes we did not see any immediate, noticeable change, but if you left the potato in distilled water for long enough, you will notice that the weight of the potato should have increased.

We recorded the weight of each potato piece, before we had put it into the test tube – filled with distilled water, and than left it in their for some time. We than took the potatoes out to see how much the weight is changed, and so recorded the results on a table like the one below:

The results on this experiment show a significant increase. As you can see from the table, as you make more pieces the percentage increase gets higher. When you cut the potato cylinder into two the weight does increase and so the percentage increase will be high. If you look at the last column, where the potato cylinder is cut into ten parts, the weight increases a lot and the percentage increase is higher than if you cut it into two.

We did the experiment again and these where the results that we got:

As you can see, apart from the one anomalous result, by looking at this next results table, we are given the same pattern: as you make more pieces the percentage increase gets higher. When you cut the potato cylinder into two the weight does increase and so the percentage increase will be high. If you look at the last column, where the potato cylinder is cut into ten parts, the weight increases a lot and the percentage increase is higher than if you cut it into two.

We did the same experiment a third time, just to make sure that we are getting fair results, and this is what we got:

This experiment also has a couple of anomalous results but if you do not look at these anomalies, you can clearly see that if you increase the number of pieces, you increase the percentage increase.

This last set of results is the average percentage increase of weight, in the potatoes. I found out the average by using the three sets of results above.

Analysing Evidence & Drawing Conclusions

After doing the experiment and examining the results I can now say for sure that my prediction was right, that the more pieces there are the more water the potato will take in and that if I double the surface area exposed in water, then the speed of osmosis will also double. This means the potato will increase in weight faster because water tries to enter its cells and dilute the sugar content inside.

I found out that osmosis would occur faster if you increase surface area, by increasing the surface area of the potato, there are more places that water can enter the potato.

You can easily draw a conclusion that this theory is correct by looking at the results, and by looking at it in the form of a graph.

This graph shows the average percentage increase of the potatoes weight. The results were taken from the table above.

You can see clearly that on the graph there is an anomalous result, where it shows the result of eight pieces. This is more clearly seen on a graph than on a table. The graph shows that the more pieces there are the more water the potato will absorb. So if you increase the surface area of the potato you are simply making it easier for osmosis to occur.

This next graph shows the results we got from the first experiment.

The dotted line on the graph simply represents the weight of the potato before we left it in the distilled water and the other line represents the weight of the potato after it had been left in the distilled water.

After doing this experiment I can now conclude that by increasing surface area of the potato cylinder osmosis will occur faster. I have shown this through graphs and tables.

I think that my graphs turned out like it did, because of my prediction, which I stated in my planning. As the surface area of the potato increased, the percentage increase became larger; this was because the water molecules were entering the cell to even out the concentration gradient. The lower the surface area (less pieces cut), the less water entered the cell, and therefore the lower the mass of the potato gained. This was the case for when the potato’s surface area was low, as there was a small increase of mass when it was cut into two because not much water molecules were entering the cell to even out the concentration gradient.

Evaluating Evidence

The procedure that we used was correct. There was no fault in our method, and the method is not why we got the anomalous results.

We could have used other methods though. We could have increased the amount of sugar in the water, and see if this affected the results, or the temperature, or the time the potato is left in the solution.

The results that we got for the three experiments were completely different because we had left the potato cylinders in the test tubes for different amounts of time. For the first experiment we had accidentally left the potato cylinders in the distilled water for about sixty-three hours, this is why there was a significant percentage increase of the potato’s weight. The second set of results did not have such a big percentage increase because the potato pieces were only left in the test tubes for approximately seventeen hours, and in the last experiment we had left the potato’s for only two hours and this explains why the potato pieces did not absorb as much water and gain a lot of weight.

The accuracy of the results was not exactly strong because as you can see by looking at the graphs we got quiet a few anomalous results. If you look at the table, which shows the average percentage, increase of the potato’s weight, and than look at the result we got for the potato cylinder cut into eight, there is an anomalous result. This anomalous result could have occurred by dirt or dust. If any dirt got onto the pieces, and so was not completely clean, this could have affected the results. It would have affected the results because the dirt would stop any water entering the potato in that area. Or the anomaly could have been caused by not being spread out. If the potato pieces are all touching each over, this will decrease the amount of surface area. There are many reasons why some of the results might not be accurate; when I took each chip out of the solution and then measured them, many of the chips were still wet, and had drips of the solution on the surface. These drips from the solution would have caused the chips mass to be higher then it actually was. Another reason could have been that; the overall temperature of the laboratory was quite high and there was heat from the sunlight that was coming through the windows. As I was taking the chip to be weighed this could have caused some of the water in the potato cells to evaporate. With some of the water evaporated from the chip, the mass of the chip would have decreased from what its mass was when it just left the tube, causing inaccuracy within my results. It could also be that the chip’s mass decreased because, when I was trying to remove each chip from the test tube, I had to either squeeze hard with the tweezers, or push the chip hard against the side of the test tube to scoop it up. This pressure exerted on the chip could have either caused small bits of it to break off. It could have also caused some of the water to be squeezed out of the cells of the chip, though probably didn’t have a drastic effect on the mass. The one anomalous result that I collected could have been because of water being evaporated from it and because of the force I used to get it out of the test tube.

Apart from this one anomaly we can still make a firm conclusion that if you increase the surface area of the potato you will increase the amount of water that will be taken in, therefore if you double the surface area the percentage increase, of weight, should also double.

How I would make my experiment better, would be that when I took the chip out I would use my finger and wipe the surface, making sure that there wasn’t too much water on the outside affecting the mass. To make sure that there was as little evaporation as possible, I would do my experiment nearer to weighing machine and I would have a fan working next to my experiment, this would make the air around the chips as cool as possible. Also, the way I would remove my chip from the test tube would be that I would pour the content of the test tube into a sink, but catching the chip in my hand. This way I wouldn’t put so much force on it.

HAMMAD NAVEED