Safety
Safety is a very important aspect in any scientific experiment. This is emphasised in this osmosis experiment. The following rules and procedures should be taken into account when performing this experiment.
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Wash hands. If you are going for a clean experiment you should start with your hands.
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Tie back long hair. This does not apply as much for boys, but girls should be warned.
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Wear an apron. You do not want acid or any other substance ruining your clothes.
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Do not run. Always walk and take your time in a laboratory, and be careful of what’s happening around you.
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Handle items with care. Any sensitive items must be handled gently, and carefully.
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Do not throw anything. All items must be placed or passed gently.
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Be careful with knives. When cutting the potato keep your fingers away.
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Take care with the acid. Acid can burn and even kill. Pour it slowly and always put the lid on it afterwards.
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Wash hands. After the experiment wash your hands again.
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Pack away sensibly. Return everything properly, report spillage’s or breakage’s and do not mess around.
Variables
Variables are things I will and will not be changing during this experiment.
Controlled Variables
The following things are controlled variables. I will be able to change what happens and what they do together.
- Acid concentration. I can change the molar content of the acid.
- Time. I can change how long I time for.
- Water volume. I can change the volume of water.
Independent Variables
The following things will go on and I cannot change them. They are usually outcomes of controlled variables.
- Potato weight. The weight of the potato before and after it is placed in the acid cannot be changed (unless I deliberately make the potato smaller by cutting it)
- Weight change. The change in weight of the potato is an outcome and can be different all time. I cannot change it.
Results
Experiment Number 1:
Experiment Number 2:
Experiment Number 3:
Experiment Number 4:
The Average Experiment
This is the table showing the averages of the previous 4 experiments. I will describe this set of results later in the investigation.
*NB: When we performed the experiments, there was no sugar concentration 0.2 available, so we had to miss that one.
**Correct to 1 Decimal Place
Analysis
By looking at the table above, we can see a number of different links and connections. These are all related to the weight of the potato, and in places there is no connection.
The first link is between the sugar concentration and the weight before osmosis happened. The lower the sugar concentration, the heavier the potato weight before osmosis. This is also true for after osmosis as well. At 0.0 (water), the potato was heavy at 6.0g and after osmosis it was 5.9g. but at 1.0 concentration, the weight before was 5.5g and after 5.6g, so there is a link. The lighter the potato weight before and after osmosis, the larger the sugar concentration it is placed in.
Now we move onto the change in weight. The only time the weight decreased was at the lowest value, 0.0 (water). From then on, everything else increased. As we had no reading for 0.2, we shall guess it and say it was approximately 0.0g change in weight. So there was no change in weight there. Practically all the readings have increased in weight by 0.1g. however, at 0.6 concentration level, it increased by 0.4g, which is way above the rest. This is most likely an anomalous result.
Conclusion
My previous prediction stated “if you increase the level of sugar concentration in the mixture, less water will be passed through the potato chips cells”. This prediction is correct. The analysis of the results shows why.
When I actually performed this experiment, not much happened. As the potato was placed in the acid, no reaction could be physically observed. It was quite boring! But I could tell osmosis was taking place because of the change in weight afterwards.
I will now explain the results. The reason why there is no connection between the change in weight and the level of acid refers to my background knowledge. (Appendix A).
With a low level of acid the potato will be plasmolysed. The strong cell wall wills shrivel up, thus, letting more water through. But if you increase the acid from the onwards, only a small change will take place because the osmotic strength of the cell wall will remain constant.
The small change in the weight of the potato is affected by how much the wall expands or shrivels up depending on how strong the acid is.
Evaluation
There is only 1 major anomaly that can be seen from the results. The change in weight when the sugar concentration was 0.6. All others around this concentration were plus 0.1g but this was plus 0.4g. There are many reasons for this high result. It could have been:
- Time – I could have removed the potato too late or put it in too soon
- Potato – the potato could have been covered in an unknown substance
- Sugar – the concentration may have been altered and not what it said it was
- Me – I could have accidentally changed the sugar concentration.
I had no problems with this experiment. The instructions were easy to follow and carry out. All I had to was collect the equipment ad run the experiment.
If I was to repeat this experiment I would make sure that I had an acid level for 0.2 and the main thing would be to make all the potatoes weigh the same. Approximately 5g. this would make it fairer.
Future experiment would involve performing the osmosis on an animal cell and even different plant cells to see if that makes a difference. I could try different levels of acid, or make a new variable instead of the sugar concentration.