Prediction
I predict that the larger the mass of the alkane the slower the ball bearing will fall, for example the ball bearing will fall faster through Pentane (C5H12) than Decane (C10H22). This is because Decane contains twice as many atoms as Pentane. Therefore it must take the ball bearing more time to fall through Decane as the more particles the greater friction there is to slow the ball bearing down.
Hydrocarbons
Therefore, the larger the mass of the alkane the faster the velocity as the greater the amount of time foe the same distance (50cm) the velocity will be same. This is because the distance is divided by the time taken. Therefore my graph will display a negative correlation of results.
Hydrocarbons
Emma Knight
Chemistry coursework
Scientific knowledge
Some liquids hydrocarbons are very viscous, yet others have a high viscosity. In this investigation I am trying to find is there is a link between the number of carbon atoms in the hydrocarbon and how viscous the liquid is. The hydrocarbons I am looking at are the alkenes:
Alkanes Molecule formula
Butane (C4H10)
Pentane (C5H12)
Hexane (C6H14)
Heptane (C7H16)
Octane (C8H18)
Nonane (C9H20)
Decane (C10H22)
Dodecane (C12H26)
Hexadecane (C16H34)
General formula = CnH2n+2
The steel ball bearing will fall faster through ‘runny’ oil than through higher viscous oil.
As well as looking at the time it takes for the ball bearing to fall through the glass tube I will also look at the velocity. Velocity is like speed, it tells you how fast something is moving. But it also tells you the direction something is travelling. To calculate this we use a simple equation:
Average velocity = distance moved in a certain direction / time taken
m/s =meters/seconds
One way of showing which way something is travelling is to and + or-. For example:
+ 10m/s (velocity of 10m/s to the right)
10m/s (velocity of 10m/s to the left)
However, I will be taking my results from 90°, up right not tilted.
Sir George Gabrielle Stokes studied this looking at how spheres flow through different liquids columns under the influence of gravity. He worked out that the force acting in resistance to the fall was equal to 6rv, where r stands for the radius of the sphere, is the viscosity of the liquid and v is the velocity of fall. The force acting downward is equal to 4/3r3 (d1 - d2)g, where d1 is the density of the sphere, d2 is the density of the liquid, and g is the gravitational constant. At a constant velocity of fall the upward and downward forces are in balance. Equating the two expressions given above and solving for v therefore generate the required velocity, expressed by Stokes's law as:
v = 2/9(d1 - d2)gr2/
To work out the velocity in my investigation I will use the simple equation, however if I were to extend this I could explore stokes’ law and try taking results from other angles.
Emma Knight
Chemistry coursework
My results
Class results
From these results some stand out straight away to be anomalous, for example the Octane set of results. The results for Octane were very inaccurate, this could have been caused by the fact that the alkane inside the glass tube was very cloudy, which may have affect the amount of friction caused by the alkanes atoms. However, other could have been because some of the hydrocarbon in the glass tube could have evaporated before I could take any results.
From the class results I am only able to look at the time it takes for the ball bearing to fall, however with my results I am able to look at the velocity as well. I notice that my results are more accurate than other results in my class. I have calculated the accurately of my results and for all of them except for Octane that it stays below 5% accurately. To calculate this I did the following:
Accurately = . ½range .
Largest number + ½ range
From calculating the accurately I know that my results are very accurate. If I look at my graphs I can see that for each set of experiments Octane stands out by far as I is complete anomalous but if I ignore this set of results the rest are fairly even.
The line of best fit shows that my prediction is correct that the higher the mass of an alkane the slower the ball bearing will for, therefore the faster the velocity. So for Butane I can predict that it will take 1.2seconds for the ball bearing to fall 50cm and it will travel at a velocity of 0.41m/s. I can also predict for Heptane, as I was unable to
Emma Knight
Chemistry coursework
take results for this alkane. I predict that it would take about 1.34 seconds for the ball bearing to fall 50cm and it would travel at about 0.38m/s. For both of these alkanes I was unable to take results for and so where the rest of the class, as there where either of these alkanes available. However, if we had take these results maybe my line of best would be more accurate and therefore my predictions would be as well. Furthermore, if I had taken more note of the radius of the sphere, the viscosity and the density of the liquid as well as the density of the sphere, I could have used stokes’ law, which would have given me strong, more accurate results for the velocity. However, this wouldn’t change results for the time it takes for the ball bearing to fall 50cms.
However, from these results I can still say that they back up my prediction that the line of best fit shows the coordination I expected. For example the line of best for the time it takes the ball bearing to fall 50cms has a positive coordination which I had predicted the greater the mass of the alkane and greater the amount of time it takes for the ball bearing to fall. Similarly the line of best fit shows a negative coordination as I had predicted the larger the mass of the alkane the faster the velocity. Though I have been able to find the mass of each alkane I know that the larger the number of atom the greater the mass must be. As the number of atoms increases the greater the friction on the ball bearing causing it to fall slower.
Butane Hexane
Notice that in Hexane the ball bearing has to past through more atoms than Butane, therefore more friction is caused in Hexane slowing the ball bearing down.
Evaluation
From looking at my results and comparing them to the classes I can see that mine are more accurate than others. As well as comparing them with others for accurately I calculated the accurately, if I ignore the whole set of anomalous results for Octane they all had an accurately of under < 5%. However, by ignoring the results for Octane I can draw an conclusion for the time it takes for the ball bearing to fall 50cms and the speed of the velocity. The Octane results were cause probably because the alkane was cloudy, affecting the atoms and how they affected the friction causing the ball bearing to slow down. Other anomalous results could have been caused by some of the alkane evaporating and therefore I was taking results of glass tubes with liquid in of less than 50cms or I could have taken different results from stand on at the glass tube at different angles. However, my method must have been reliably as it gave clear, even results if you ignore the set for Octane. For example, my accurately for Hexadecane was < 0.9%, showing just how accurate my method was. However, the average
Emma Knight
Chemistry coursework
accurately was < 3.34% with Octane, moreover without Octane my average accurately was < 2.78%, proving my method to be fairly accurate and reliably. In my results the lines of best fit for both the time taken and the velocity of the ball bearing support my prediction. The lines of best fit show how I expected the graphs to look. Giving a positive coordination for the time it takes for the ball bearing to fall 50cms and a negative coordination for the speed of velocity. This proves that the greater amount of mass (atoms) the slower the ball bearing will fall, and the faster the velocity. However, I know that the mass of the alkane does not affect the velocity by looking at the equation:
Average velocity = distance moved in a certain direction / time taken
m/s =meters/seconds
As the ball bearing takes longer to fall through the same distance the velocity becomes slowly smaller. Therefore my results showed this.
However, to improve or to extend my results I would have to take more tests for each experiment and maybe see how different angles affect the time and velocity. I could take more notice of the size and density of the sphere and the density and the viscosity of the liquid, which would allow me to use Stokes’ law to have more accurate results for the velocity of alkanes. Though to improve this investigation I could take a larger range of results repeating them ten times, which would give a stronger average. As well as changing the Octane I used.
