From this preliminary testing I have decided to put the slide at a height of 2cm with each alkane in a cooling water bath to keep it below room temperature (less chance of evaporation) and to place 2 drops of alkane on the slide for each repition so that there is less chance of all the alkane evaporating.
Final Experiment
Equipment List
- Pentane
- Hexane
- Octane
- Decane
- Glass Microscope slide
- Dropper
- Plasticine
- Ruler
- Stopwatch
- Tissue (to clean Alkanes off slide)
- Water Bath full of cold water.
Method
- Place Alkanes in the Water Bath
- Place Microscope slide at the fixed height of 2cm (determined from the preliminary testing) on top of the plasticine.
- Collect a small amount of the alkane in the dropper.
- Release two drops of the alkane, right at the top of the Microscope Slide,
- Using the stopwatch, time how long the alkane takes to get to the bottom of the slide.
- rinse slide under the tap and wipe the slide clean, using the tissue.
I will repeat the experiment five times then calculate the average time taken for each Alkane to reach the bottom of the slide. I will then find the speed at which the Alkanes flowed using following equation:
Speed = Distance
Time
Fair Test
- The Microscope slide must be cleaned at the end of each repetition.
- Each alkane must have its own individual dropper.
- The plasticine must support the slide in such a way that the liquid will not flow of the side of the glass.
- The height of the slide must remain the same during every drop.
- Each drop should have the same amount of liquid.
Safety
- Alkanes should be kept away from naked flames
- Safety goggles should be worn so no chemicals get in the eyes.
- Any spillages should be cleared up at once
- Must have good ventilation
- People with long hair should tie it back.
Prediction
I predict that pentane will have the lowest viscosity followed by the hexane, then octane and then decane. I also predict that pentane will be half as viscose as decane.
Reasons for my prediction
Viscosity is a liquids resistance to flow. The longer the chains, the more force there will be between the carbon atoms and hydrogen atoms so the more tangled the chains will get. So the longer the chain is, the more viscous the alkane is and the slower the alkane will flow. So Decane will be the most viscous, then octane, then hexane then pentane because Decane has the longest chain, then octane, then hexane and then pentane. So Pentane will be the quickest Alkane to run down the slide and Decane will be the slowest.
Speed is calculated using this formula:
Speed = Distance
Time
Analyis
I have found from my results that the longer the chain the Alkane has the more viscous the Alkane is, so the slower the Alkane is when running down the slide. Pentane is the least viscose of the alkanes tested and Decane is the most viscose. Pentane, which has 5 carbons, was the quickest on an average time of 1.968 seconds at 3.81 cm/s. Then Hexane with an average time of 2.54 seconds at 2.95 cm/s. Then Octane with an average of 4.766 seconds at and then Decane with an average of 9.942 seconds at 0.7575 cm/s. So the longer the chain is in a Alkane the more viscous it is because the carbons are packed together so the thicker the alkane is so the slower the alkane runs down the slide. . In my prediction, I predicted that the longer the chain of carbons and hydrogen’s there is in the listed alkanes, the more viscous the alkane will be, so the slower the alkane will run down the slide. So Decane would be the most viscous, so it would take the most time to run down the slide and pentane would be the least viscous and would be the quickest down the slide. So my prediction was right. From my table of results above, I can see that there are a number of Anomalous results, i.e. Octane Test 1 (6.6 seconds), Decane Test 2 (15.42 seconds) and Decane Test 4 (14.75 seconds
Evaluation
My experiment did work quite well in the end although I did have to repeat many anomalous results. However my experiment over ran into 2 lessons, which were on different days so the equipment I used was different so this made the experiment unfair. My results are quite accurate, but it wasn’t accurate enough basically because the experiment wasn’t accurate enough. For example I am not sure if the droplet of each alkane was the exact amount for every repeat, the droppers were not very accurate, and the alkane could have evaporated whilst flowing down the slide. Also the Plasticine was put in the oven before the experiment; this could have caused the alkanes to evaporate quicker because it caused the slide to become slightly heated. I used 2 different sets of equipment because the experiment took 2 lessons and each lesson was on different days. The stopwatch wasn’t accurate on stopping at the exact time. The experiment could be improved by using a machine to measure out exact amounts of alkane to drop on the slide and a machine to time, so it stops at the exact point where the alkane gets to the bottom of the slide and to make sure the same equipment is used if the experiment over runs and to make sure the plasticine is at room temperature. I could also use an Automatic Data Logger to log the position and speed at certain intervals whilst the Alkane is flowing down the slide. A logging interval of 0.1 seconds or 10ms would be sufficient to accurately measure the speed of the alkane. Data Logging is more accurate than humans, and can take measurements in which humans cannot survive. Improvements to this experiment could be droppers with narrower funnels to contain the liquids better, fresh microscope slides after each repetition and a proper water bath or fridge to keep the alkanes at a set temperature. A viscometer could also be used. The alkane could be placed in a tube, a grain of rice would then be placed in the top and it could be timed from start to finish with greater ease and would be far easier to see. My results helped me to draw to a scientific conclusion by showing that the longer the chain is the slower the alkane went.
