High Osmotic Potential low osmotic potential
I predict that the chips left in a solution with a high osmotic potential will gain water, this is because potato chips contain sugar, salt and water therefore the concentration of water in a potato is low and water will move into the chip from the solution. This causes the potato chip to gain water and become hard. If the concentration of solution is greater outside than the chip, then it’s hypnotic.
When the potato chips are placed in a solution containing a lower concentration free water particles outside the cells than in, water leaves the chips by osmosis. The cells become flaccid due to the water departing the chip at a faster rate than it enters. A flaccid cell is weak and unsupported, and its membrane is withdrawn from the cell wall. Therefore it is soft.
A Flaccid Cell:
Cell Wall
Cell Membrane
Vacuole
Nucleus
Low Osmotic Potential High Osmotic Potential
A potato chip in a solution with a low osmotic potential such as salt solution will lose water, as there will be a low concentration of water molecules outside the potato. The loss of water from the potato chip will cause it shrivel and become soft. If the concentration of solution is greater inside the cell as it is outside, it is called hyper- tonic.
I am aiming to find the concentration of salt solution that causes the potato chips to neither swell nor shrink. This solution would therefore have to contain the same concentration of free water particles outside the chip than there would be inside the cells, so that equilibrium would be achieved, allowing the water to enter and leave the cells at the same rate, by osmosis. This would therefore cause the chip to neither swell nor shrink.
A potato chip in a solution with a low osmotic potential such as salt solution will lose water, as there will be a low concentration of water molecules outside the potato. The loss of water from the potato chip will cause it shrivel and become soft. If the concentration of solution is greater inside the cell as it is outside, it is called hyper- tonic.
Osmosis is the passage of water using diffusion from a region of high water potential through a semi- permeable membrane to a region of low potential until the solution reaches its isotonic point. The isotonic point describes the point in which osmotic pressures are equal and osmosis stops. This is what Kathy is aiming for and it also what I am trying to find in this investigation.
Diagrams Of Apparatus:
Apparatus:
- White potatoes
- Core borer size 6cm
- Beakers 250cm
- Distilled water
- 0.5 molar salt solution
- 1.0 molar salt solution
- 1.5 molar salt solution
- 2.0 molar salt solution
- 30cm ruler
- Scalpel
- Top pan balance
- White tile
- Pipette
- 15 test tubes
- Test tube rack
- Measuring cylinder
- Kitchen roll
Preliminary investigation:
Method
- Cut 15 slices of potato chips using a cork borer which will be size 6 and cut to 3 cm in length
- We will then measure out 5cm of different salt solutions using a measuring cylinder then pour them into labelled test tubes then place them in the test-tube rack
- We will weigh each potato chip and record
- We will then weigh the 15 potato chips then place each of them in the test tubes in the appropriate solution.
- Left for 48 hours for Osmosis to take place
- We will then drain off the salt solutions and re-weigh the potato chips.
- Work out the mass change over 48 hours and the rate of osmosis
- We will then record the results and plot a graph.
Results table
Key: Dw = Distilled Water
M= molar
Preliminary Conclusion
I seemly accept that the size of the chips 3cm and the volume of solution, which was 5cm ,are appropriate and I wish to use the same amount of chip and volume of solution in the actual experiment. The distilled water gained mass (water) and each of the salt solution increased the loss of mass was greater. Looking for the osmotic potential I found that it must rest between distilled water and 0.5 salt solutions. Therefore I am going to repeat the experiment but using Distilled water, 0.1m, 0.3 0.4 and 0.5 salt solution.
Fair test
Given the mistakes made in the preliminary experiment there are a few areas where care is essential. There are also some constants, which must remain the same:
- All of the potato slices must be placed in the solutions simultaneously.
- All potato slices must be fully submerged.
- All of the potato slices must remain in the solution for 48 hours.
- The same potato will be used to bore slices out of.
- Keep the temperature the same (room temp 23°C)
- Make sure the concentrations are divided up carefully, using a measuring cylinder
- Make sure the potato pieces are the same size
Safety
When conducting my experiment I will be making sure I don’t harm my self or anyone else by always cutting up my potatoes on a ceramic tile. The use of the knife could be dangerous as there is a sharp blade. To be safer, I will keep the blade tucked away when it is not in use. Also I will keep my hair tied back as to not get in the solution. I also wore a lab coat to prevent my clothes coming into contact with any chemicals that could be still on the bench.
Method:
We executed the experiment exactly as we carried out in our Preliminary experiment. However, there were some few minor changes. For example, the solutions to be used are between distilled water and 0.5 salt solutions.
Blank Results table
Percentage change in mass= Average change in mass X 100
Average potato chip mass
Results table
Analysis
In this investigation we found out that if you put a potato piece in salt solution with less water than the potatoes then water molecules will move out of the potato and into the surrounding salt solution, therefore the potato piece would decrease in mass and size. If the potato piece however has a low concentration of water than the surrounding salt solution then the water molecules in the surrounding solution will move into the potato piece, and the potato piece will increase in mass and size. This is clearly shown in our average mass change of a potato piece in salt solution and of distilled water.
From looking at the results, it can be seen that as the quantity of salt solution is increased, the mass of the potato decreases. For example in pure water the mass of the potato changed by +0.16 grams but in 0.2 molar salt solutions the mass decreased to by -0.03g, showing a loss of mass in the potato. The % change was notably greater between distilled water, 0.1 molar salt solution and 0.2 molar salt solution but after 0.2 molar salt solution the percentage change becomes less dramatic and shows a steady rate of balancing out as there is only so much water a potatoes can loose.
The reason all of the above happens is osmosis. Osmosis is the movement of water molecules from a high concentration to a low concentration through a semi- permeable membrane. When chips are left in distilled water or 0.1 molar salt solutions they gain mass, therefore water. This occurs in a solution, which has a higher concentration of water than the potato so osmosis occurs and water enters the potatoes. The vacuole fills with water and the cell gets turgid. This is why Cathy’s chips went hard and it agrees with my prediction.
From the graph I can see that the more concentrated the salt solution the more the potato piece decreases in mass. In 0.2 – 0.5 molar salt solution the chip looses mass because there is a higher concentration of water inside the potato than in the solution therefore osmosis occurs and the water moves out of the potato, the vacuole collapses and the chips go flaccid. This is why Cathy’s chips went soft and it also agrees with my prediction.
In conclusion I can see from my results that where the line crosses the x-axis the potatoes mass does not change. This is at 0.11 molar salt solution. Here the potato must have the same concentration of water, as the solution as it does not lose or gain mass/water. This is isotonic solution I mentioned in my prediction and this is the solution Cathy is looking must use.
Evaluation
We obtained the results that we predicted because the distilled water gained mass and salt solutions lost mass. My results are accurate as the distilled water and 0.1 molar salt solution gained mass in a similar amount and 0.2,0.3,0.4,0.5 molar salt solutions lost mass to a similar amount. There is one anomalous result, which is 0.4 molar salt solution this might have occurred because the chips may received different lengths of time for blotting, before weighing the chips mass after it had been in the salt solution. Another factor which could of affected the result is might have been left longer in the solution than the others, which meant more water loss.
Problem with this method of experiment is that when we began the experiment the mass of each chip was not the same and neither was angle of each chip at the ends. I would also say that the chips and different amounts of time spent in each of the solutions, as they were not put into the solutions at the same time. The method we used to take of the excess water off was not accurate as we could have spent long on one individual chip, we could blot the chip too much or too less causing an anomalous results.
To improve upon our method we may have used more potatoes to get the 18 chips as using just one potato meant that we had to be careful to not make mistakes when cutting the chips. We ought to have made sure prior the experiment that each of the chips mass weighed the same. We could have used a machine to cut the chips making the experiment a fair test and leaving no room for errors. We may have also rolled the potato chips on the paper towel a distance of 10cm for each, to remove the excess water.
Furthermore we could have investigated between 0.1m and 0.2m salt solutions to find out exactly where the isotonic solution is, such as 0.11m, 0.12m, 0.13m, 0.14m and etc. We could investigate another factor for to work out an isotonic solution such as the type of potatoes used.
