The chips placed in a solution 0.4M will lose weight but only a fractional amount compared to the amount of weight lost by the potato chips placed in 0.6M or 0.8M. This is because the difference in concentration inside and outside of the potato has a difference of 0.06M and so the potato doesn’t lose too much water thusly the potato doesn’t lose too much weight. When the potato is placed in a solution of 0.4 molar I think that the potato’s weight will stay around the same as the difference in concentration between the outside and inside of the potato is only 0.06 molar apart.
Apparatus
We will be using the following list of equipment to perform our experiment:-
- 15 Test tubes :- 3 filled with 0.0 molar solution
3 filled with 0.2 molar solution
3 filled with 0.4 molar solution
3 filled with 0.6 molar solution
3 filled with 0.6 molar solution
- 1 Potato producing 15 potato chips
- 1 cork borer (used to cut the potato chips)
Method
- Take a large potato and cut 15 X 20mm potato chips with a borer measure with a ruler to ensure that they are all the same length.
- Weigh each potato and record their weights in a table
- Measure 3 X 25ml of the following solutions 0.0M
0.2M
0.4M
0.6M
0.8M
with a measuring cylinder and place them into 15 test tubes.
- Place the 15 test tubes in a test tube rack and place the 15 potato chips in the tubes. Put a bung in each to prevent the solution from evaporating.
- Leave for 24 hours in an area where there is plenty of sunlight so that osmosis can take place.
- After 24 hours remove the chips and dispose of the solution.
- Weigh the 15 chips and record the readings.
- Calculate the averages and record in a table. Those that have lost weight will be left as concentrated potatoes (meaning that they contain less water and more solute) they will look flaccid. Those that have gained weight will be diluted potatoes as they will contain more water than solute these will be turgid.
In order to ensure that our investigation is a fair test we are going to keep the following things the same: -
- The length and width of the potatoes
- The same type of vegetable (potato), and we will take all 15 chips from the same potato
- The length of time they will be left for
- They will all have a bung placed in the top of the tube
- None of the potatoes will have any peel remaining on their surface
- Whilst the ambient air temperature is not constant, as the potatoes are adjacent to each other they will all have similar temperatures
- The above applies to the amount of light also
To guarantee the teams’ safety we will all be wearing goggles to prevent any splashes of solution getting into our eyes. We will be careful whilst cutting the potatoes to size and we will be using a white tile to prevent any slips. After we have completed the experiment we will wash our hands thoroughly to escape any irritants on our skin.
Diagram
Here is a diagram of the investigation set up. They will all be placed near to the same window for light.
Note: All 15 test tubes haven’t been included
Results
I will be recording my results in this table, all averages are to 2 decimal places: -
Analysis
As you can see from my graph, the line of best fit crosses the X-axis. At this point there is no Osmosis taking place. We know this as the weight of the potato hasn’t changed when the line crosses the X-axis and so no water has had to move to balance the concentrations. The point at which it crosses the X-axis is the concentration inside the potato. The average concentrations of my potatoes are 0.41 M.
From my graph (above) you can see that when the concentration of the solution is below 0.41 M the potato gains weight especially when the concentration is exceptionally low such as when the concentration is 0.0 M (the lowest) the potato is at its heaviest (0.33g). This is because water moves into the potato due to there being less water inside the potato than outside of it, so water moves in due to osmosis and causes it to put on weight and become turgid.
A potato placed in a solution of 0.0 M will gain the most weight in this case because the most water has to move in to balance the concentrations both inside and out. So compared to a potato placed in a solution of 0.4 M the potato will not gain a lot of water to balance up the concentrations because they have similar concentrations both inside and out. The same applies for the highest concentration which is 0.8 M as the most water moves out and so the most weight is lost.
I.e. The lower the concentration the heavier the potato
From my graph you can see that when the concentration is higher than 0.41 M the potato looses weight, particularly when the concentration was at its highest in this case 0.8 M when the potato lost an average of 0.34g. This is because the solution that the potato was placed in was the most concentrated and so the most water from inside the potato had to move out to balance it. The potatoes placed in concentrations above 0.41 lost weight, because the concentration outside of the potato was lower than inside and the water from inside moves out to balance the concentrations through the process of osmosis.
I.e. the higher the concentration the lighter the potato
My prediction was both correct and incorrect. It was correct because I stated that if the potato was placed in a solution of 0.0 M or 0.2 M the potato would gained weight and 0.6 M and 0.8 M the potato lost weight. But it was incorrect as the actual concentration of the inside of my potato was essentially 0.41 M and not 0.34 M which was what I predicted. So when the potato was placed in a solution with a concentration of 0.4 it didn’t lose a fractional amount of weight it gained a minute amount of weight. This is due to the outside of the potato containing a little more water than the inside of the potato (in effect the water outside is more dilute). A small amount of water from outside passes inside to balance the amount water both within and outside of the potato, thus the potato only gains a small amount of weight.
Evaluation
The experiment which we carried out was quite reliable. We didn’t experience any anomalous results. The information we collected was as what we expected apart from the minor difference of the inside of the potato that we experienced (as said above) this could be due to the fact that during the pilot and the actual experiment we used different potatoes.
As you can see from my results table for each concentration, each of the change in mass was either positive or negative and not mixed. As seen below.
This shows that the mass changes were quite consistent as if they were mixed the average would end up being anomalous. For example if the 0.11 was actually negative the average change in mass would be 0.29g instead of 0.51g
Despite the experiments reliability it was not completely dependable. For each concentration many of the results differed greatly. Below shows the differences between each of the results change in mass, you can see that on certain concentrations there is a vast difference between each of the figures this shows unreliability (from the change in mass) and others there is not such a great difference: -
Overall I consider the results reliable. There weren’t any anomalous results, and the differences in repeats could be the consequence of the following limitations of the experiment:-
- The concentration from the inside of the potato will not be evenly spread throughout and so different chips will contain different concentrations.
- The measuring cylinders that we used may not be very accurate
- We only used one measuring cylinder, even though we washed out the cylinder after use each time with distilled water, it is possible that not every water particle may have been removed, (water has a concentration of 0.0 M). Therefore the water may have lowered the concentration level of the solution (that the potato was placed in) and so caused it to loose or gain too much weight and affected the end result.
- Each of the potato chips may not have the same surface area (as a result of us not cutting them accurately enough, examples shown below). This could cause different amounts of water to move in or out of the potato and so causing it to gain or loose different amounts of weight.
- When we removed the potato after 24 hours, we may have put to much pressure on the potato and thusly if the potato is flaccid excess water may be lost and extra weight may not be accounted for.
- Because we didn’t blot the potatoes after removing them from the solution the residue remaining on the surface will cause extra weight to be accounted for.
- We could not control the temperature of the room and even though all of the potatoes were in round about the same area, the temperature may have been lower/higher than expected affecting the rate of osmosis.
In order to improve the experiment, it must be adjusted to prevent the previously mentioned limitations from affecting the end result of the test. (I have numbered each improvement according to what it is going to improve)
- Try to take all of the chips from the same area of the potato. This is because the closer they are together, the more likely the concentration of each chip will be similar.
- We can use a burette or a graduated pipette as they are more precise methods of measurements.
- We can use different measuring cylinders or thoroughly dry them after being washed each time.
- We can cut all of the potatoes at the same time with a longer knife. They can be placed in a straight line and sliced together and so will all have the same length and thusly the same surface area.
- Be a lot more careful when removing the potato from the solution, and ensure that not too much pressure is put on it whilst transferring it from the solution to the scales.
- Blot the potatoes. Make sure that each potato has been blotted an equal amount of times to make sure that the test remains fair.
- Place the potatoes in an incubator to ensure a constant heat.
There are many different experiments that can be carried out to see how osmosis ranges and to expand on the experiment that we have already performed such as: -
- We can use a different root vegetable to see how osmosis ranges in this type of vegetable.
- We can use a different range of concentrations. We used the even concentrations and so to get a broader idea of osmosis in potatoes we could use the odd ones such as 0.1 M, 0.3 M, 0.5 M, 0.7 M, and 0.9 M.
- To find out the actual concentration inside the potato we could use some more precise measurements of the concentrations around the point at which the line crossed the X axis on my graph. This point was 0.41 M and so we could use concentrations of 0.38 M, 0.39 M, 0.40 M, 0.41 M, and 0.42 M.
- We could repeat the experiment around our anomalous result to find out for sure what it was meant to be.
- We could carry out the experiment in different temperatures to how this affects osmosis.
In conclusion, the osmosis of a skinless potato is affected when placed in solutions with concentrations less than 0.41 M and solutions with concentrations higher than 0.41 M.