Concentration 0 M The Solution example essay topic

valuation Reflecting upon the criteria selected for purposes of this investigation, overall experiment was in agreement with the hypothesis. The set of results obtained demonstrated a clear correlation. Existing scientific logic can be applied to explain any discrepancies, which is included in the conclusion. The experiment was relatively straight forward to carry out, in the sense that the method I used was well thought out and coherent. No complex technical equipment was used either and so I was familiar with everything I used. Through looking at my set of results and the class' average results I saw that the results should produce a relatively curved shape when the points were joined dot-to-dot, overall my results achieved this, this tells me my results are quite reliable.

The fact that I also used 2 pieces of potato for each concentration and that the increases in length for each of the two pieces were quite similar suggests that the results are accurate. However, through looking at my results I can see that by comparing the % change for my 0.00 M solution to the class average, my result is significantly higher i.e. nearly twice as big. This suggests that my result must have been anomalous for this quantity i.e. an error must have occurred. The reason for this could have been improper dilution of the solution made as for the concentration 0.00 M the solution consisted of just distilled water. As a result the only reason for the anomalous result could have been human error with the measurement of the potato sample before putting it into the tuber or even after the practical was over, when I was measuring the new length.

Even though I say that my results were accurate and reliable, through looking at the graph I have drawn overleaf (of class results), you can see that there is a huge range of results, for example for the concentration of 0.4 M, the values range from 0.00 to -8.20, this huge difference in ranges between the class is present on more or less all of the individual concentration results. This suggests that there was an error somewhere along the line, decreasing the accuracy of my results. If the range was small, this would mean that the points were close together and so everyone got the same results, however this was not true meaning that there were some errors. Sources of Errors 1. The preparation of sucrose solutions. 2.

The sucrose was weighed using an electronic balance (one decimal place) 3. The purity (gradation) of the sucrose 4. The associated moisture (water of crystallization) of the sucrose 5. The 10 ml pipette used accuracy 0.1 ml 6. There was no way of measuring the molarities of the solutions 7. The uniformity in variety and the age of the potatoes used 8.

Length of the potato were measured using a ruler (accuracy +/-1 mm) 9. The sharpness of the potato cutting instrument Explanation for the large variations in the class results The fact that different potatoes were used by the class also could be another reason as to why the range of results are so large. Each of the potatoes could have had a slightly differing water potential than the rest therefore more water molecules could have moved into or equally out of the potato sample for a particular concentration, this would vary the calculated % change, again giving inaccurate results. How could my experiment be more accurate?

1. The potato segments should be measured using a micrometer. 2. The experiment should be repeated using more than just two samples 3.

The sucrose used for solution (be graded by quality control) 4. The container should be covered to exclude air borne contamination 5. Ambient temperature and pressure recorded 6. The potato was randomly wiped using blotting paper 7. The experiment should be repeated with time as a variable It is also possible that the measurements of the lengths of the potato samples may have been inaccurate (both before and after being submerged in the solution). The technique I used was just a standard ruler.

This means the results were only accurate to the nearest millimetre. The use of this instrument also left the possibilities of human error. Even though I did repeat the measurement of each sample on two occasions to ensure accuracy, I cannot vouch upon the rest of the class doing the same. This could have been resolved via the use of a simple set of weighing scales, as there is no chance of human error and are accurate to three decimal places the nearest 0.000 g (a huge amount more than the ruler) or still if we wanted to measure length a set of callipers could have been used (there is barely any chance of error with this). In each of the sucrose concentrations that I created, I placed two potato samples. Now thinking about this, if I had time to repeat the experiment again I would only place one potato sample per sampling tube.

There could have been an effect that the two potato samples together had that may have resulted in an increase or decrease in the % change. If the water potential of the solution was lower than the potatoes, the potatoes could have each given out more or less water molecules as they were as a pair. This again could mean there is an error in my results. Another place where errors could have originated from was the fact that the potato samples had to be dabbed onto blotter paper to remove excess moisture before being measured. Some potato samples may have been dabbed too much and therefore had removed too much moisture (making the length smaller). This could have again given false lengths.

Now that I have looked at all the possible sources of errors, I feel the sources that effected my investigation the most were, firstly the likelihood that dilutions were improper. This is due to the fact that I had to use pipettes, which had a size of 10 ml and were only accurate to the nearest o. 1 ml. This meant for each dilution I had to use for than one pipette full and so the errors built up. This meant the concentrations I though I made were not actually what I expected and so decreasing the accuracy of my results, as once the solution was made there is no way to tell what the molarity of a solution is.

I would have much rather used a burette which is the most accurate piece of apparatus available at measuring solutions. Secondly, again the fact that I placed two potato samples in each sampling tube. Finally, there could have been skin left on the potato sample at certain sides. In my investigation I used 1 potato to ensure I carried out my fair testing regulations. As I made the final potato samples I got were closer to the edges. This meant there might have been a layer of skin on one side of the potato or even that the potato sample may have had a non uniform diameter.

Due to a layer of skin, water molecules would have not been able to move into the plant cells or out as easily via the process of osmosis as there would be an additional layer for the water to pass through. This resulted in either an increase or decrease in what should have been the actual % change of length. I feel these were the errors that most effected my investigation. I will also compare my results to a secondary source. Below is a copy of Marilyn's data on the same experiment. Sucrose Conc.

One other similarity the two experiments have is that the water potential is -1120 Kpa (the molarity for 0% change is 0.40 M for both). However for my secondary data I have more readings and this is why there are these slight turning points that vary to that of my results, for instance in my secondary source readings were taken at molarities such as 0.25 M, 0.45 M ect. it is possible that my experiment would have also had these abrupt turns if I had taken readings at these molarities instead of keeping a constant distance of 0.10 M between each concentration of sucrose solution. However I can see that although the graph fits with my results and the class average results, if I were to take the individual class readings there would be a huge difference in results. This again points towards the fact that there were variations and errors. I know how the secondary source carried out the experiment as it came from a college technician, who gave us a plan for how the experiment was carried out. The plan was to ensure no other factors effected the final % change other than the water potentials of the solution and potato sample.

I can see one error on the results (circled on graph) at 0.25 M, this is because it is a very sharp and unexpected turn. Reasons for this error, I can only say could be down to human error. Explanation for the non conforming results The solution concentration could have been diluted wrongly, the potato lengths could have been measured inaccurately before or after the potato sample was placed in the sucrose solution. By looking at the graph for secondary data I can see that the points would fall in the range of the class results easily.

Reproducibility of results If I had the possibility to improve or extend my investigation I would primarily use a more accurate method to create the appropriate dilutions, for instance I would have used a burette, which could hold the exact amount needed in one go, rather than in two. This would have enabled me to create more accurate dilutions. I would also place one potato sample per sampling tube as I don't know if by placing two at a time I varied the final length of the samples. Using two may have meant less potato sample had to expel or consume more or less water to reach an equilibrium between the internal and external water potentials. Also, as explained before I would also have used electronic weighing scales to measure mass, instead of a ruler to measure length, as the weighing scales are far more accurate and would also leave no chance of human error. If the measurement of length was mandatory I would have felt more comfortable using callipers as there is a higher accuracy rating and less chance of error also.

Finally, I would have liked to have used concentrations closely around the 0.40 M concentration (the concentration that gave a 0% change in length) to see what the exact sucrose solution was that shared the same water potential as the potato, as the value of 0.40 M is only accurate to the nearest millimetre, the % change for 0.39 M, 0.41 M ect. could also be 0% to the nearest millimetre. I would have liked to use the following concentrations: 0.39 M, 0.38 M, 0.35 M, 0.41 M, 0.42 M, and 0.45 M. This would consequently give me a more accurate figure for the water potential of the potato. I would have also made each of the solutions separately so if an error was made in one solution, it would only affect the results for that concentration, rather than the results for all the concentrations. Reliability, reproducibility and accuracy Now that I have looked at the way in which I carried out my investigation and also compared it to secondary data, I feel my results are not as firm as I previously imagined them to be. The fact that the class ranges are so far apart illustrates that there were operator variations in results, decreasing both the reliability and accuracy of the results. Taking this into account, the results obtained I have acquired as a result of this investigation are only a suggestion of what should happen i.e. a decrease in validity.

The investigation did work, in that my results matched the theoretical predication, but the degree of accuracy is not so great that if I repeated the investigation again, that the turning points in my practical would be the same again and again i.e. I couldn't say with any conviction that the % change for any potato sample with a length of 3 cm when put in a 0.40 M solution would be 0.00% or equally the % change for a potato sample placed in 0.00 M solution would be +15.0% or even close to that.