-paper towels
-water
-pipette
-marker pen
-timer
-ruler
Prediction- I predict that the oils with the most carbon atoms e.g. Dodercane and hexadecane will go down the microscope slide the slowest as it is the most viscous because its molecules are the biggest this means that they are the strongest and don’t break as easily.
Key factors to vary- I am going to change the type of oil I use in each experiment because they all have different sized molecules.
Key factors to control- I am going to control how much of the oil I drop out of the pipette, the level of the microscope slide on the wooden block, I keeping the line on the slide the same, and the level of the wooden block compared the level of the bottom of the slide. I’m going to and get all my results in one day, as I might not be able to use the same equipment and the plastercine might be bigger or in a different place.
Extent and range of evidence- I am going to use 6 variables with 3 repeats this will make my data accurate and reliable.
Precision and reliability of evidence- I will make sure that I drop the same amount of oil on the cross made by the lines on the slide and on the same spot every time, I will make sure that I clean the microscope slide thoroughly so not to make the experiments after unreliable because this will then make my final graph not accurate. I will clean the slide with paper towels only because if I use water it will make my results unreliable because water has no carbon atoms therefore it will make the oils go quicker down the slide.
Detailed scientific knowledge – All hydrocarbons have a spine of carbon atoms. Molecules that belong to the alkane family contain no carbon-carbon double covalent bonds. They are saturated hydrocarbons.
Things that change when molecules get bigger-
1. Physical state- they are gas when they have small molecules, but when they have bigger molecules and they have stronger intermolecular forces it makes them liquids and even solids.
2. Boiling point- because larger molecules have stronger intermolecular forces which means they need more heat to break.
3. The viscosity of oil- when molecules are bigger and they have longer chains and stronger intermolecular forces, they stick together and form even longer chains which give bigger surface areas which in turn make them more viscous.
Small molecules Large molecules
Relevant information from trials-From the trialings I did before the proper experiment, I found out that dropping 2 drops of oil from the pipette runs drown the microscope slide too quickly and would be too difficult to time it accurately from both 3cm high and 4cm high. Then I tired 1 drop of oil at 3cm high but it ran too slowly and would make my experiment go over the one day, so I decided to do 1 drop of oil with the microscope slide 4cm high from the bottom of the wooden block.
Results
Precision and skill- In my table I found that there were a few anomalous results, so I first drew a graph that represented the results including the anomalous ones and then a graph without them. To make the average of my results accurate I repeated them 3 times and then found the average. The anomalous results are highlighted in the table.
Conclusion supporting prediction-
In my prediction I stated that the oils with the most carbon atoms will go down the microscope slide the slowest, this means that my prediction was right as my graph shows. This investigation shows simply that the more carbon atoms there are in an alkane the viscous the oil is.
Detailed scientific knowledge
From my graph it also shows that the reason from my prediction was right that the oils with the most carbon atoms e.g. Dodercane and hexadecane will go down the microscope slide the slowest as it is the most viscous because its molecules are the biggest this means that they are the strongest and don’t break as easily.
Evaluation
Quality of evidence and anomalies
I think I had good quality evidence as I had a good range of results and I repeated them 3 times each. Although I did get a couple of anomalous results as shown from the graph, I highlighted these on the table and then ignored them and drew another graph showing a more accurate investigation.
Suitability of procedure
I think my method was suitable for the time I had to collect my results and to make sure that everything was a fair test and each experiment was the same each time.
Changes to improve
If I was to do this investigation again I would change some of the things I did so I wouldn’t get as many anomalies, although I still think I can support my conclusion from my graph because it is scientifically correct but the things I would change would be: I would make sure I would use the same person for each experiment because I used different people to start the timer and to drop the oil out of the pipette onto the slide, this might of effected the results because people have different reaction times and this could of made a lot of difference to the results. I would make sure that next time if at all possible to do all the “result collecting” on the same day so all of the same equipment could be used, because when I did the experiment this time it was done over a couple of days and I couldn’t make sure if I was using all of the same equipment. Also I was unable to completely sterilise the glass slide after it had been in contact with each type of oil, this may have made my results unreliable. Lastly I couldn’t be sure whether the same amount of oil was dropped out of the pipette each time .All these could have contributed to the couple of anomalies I collected.
Further work- you can also test the viscosity of oil by heating them up and using their boiling points as a variable to compare the oils and see what is the most viscous. As oils get more viscous their chains of molecules get longer which means that they become stronger to break apart when they are exposed to high temperatures. I could set up the experiment with a Bunsen burner and beaker containing the oil, and then see how long it takes to boil, although this maybe difficult as oils have very high boiling points.
Diagram
