Chemistry Design Prac Essay
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Investigate one chemistry related factor on the deflection of the liquid flow in the presence of a charged rod
How will the amount of time spent rubbing a glass rod affect the angle of deflection of flowing water in the presence of the charged glass rod?
Static electricity is formed in contact with two objects, where one object gains electrons from another, resulting in one object having a positive charge while the other having a negative charge.
Some materials tend to lose or gain electrons during contact with other objects. Materials with electrons bonded to it weakly, tend to lose electrons while materials with fewer electrons on the outer shell tend to gain electrons. Therefore, when an object is imbalanced of a positive or negative charge, it has static electricity.
Polarity is the separation of electric charges, caused when electrons are not equally shared in a molecule. This is caused when some atoms in the molecule have a higher electronegativity than others, causing more electrons to be attracted to it, leaving one side of the molecule more negative than the other. An element or molecule with an electro negativity value of 0.5+ is considered to be polar.
When a polar liquid such as water is flowing in a presence of a charged rod, the liquid tend to bend towards the rod. This is because the rod will either be positively or negatively charged, and the dipoles of the polar molecule will be attracted to the charged rod. The charge on the rod is determined by the material which is used to rub against it, however, it does not matter whether the rod is positively or negatively charged because either way, the opposite dipoles of the polar molecule will be attracted towards it, causing the flow of the liquid to bend towards the charged rod.
Defining Independent and Dependent Variables
The amount of time rubbing the glass rod with a piece of silk.
– 10 seconds
– 20 seconds
– 30 seconds
– 40 seconds
– 50 seconds
– 60 seconds
The angle of deflection of the flowing water will be measured with grid paper with a smallest increment of 1mm. A line will be drawn on the grid paper from the point where the glass rod was places to the point where the water was deflected. A protractor with a smallest increment of 0.5 degrees will be used to calculate the angle of deflection of the water.
Table 1 – Variables and Method of control
Method of Control
The rate of the flow of water
Adjust the burette to deliver the smallest stream of water possible but without being discontinuous. The water will be kept flowing at the same rate, throughout the experiment.
The glass rod
The same glass rod with a diameter of 1cm will be used throughout the experiment.
Pressure when rubbing the glass rod
Use the same person to rub the glass rod against the silk, applying the same pressure every time.
Placement of the glass rod
A line will be marked on the grid paper so the glass rod will be placed at the exact point and the exact angle to the flowing water every time.
Placement of the grid paper
The grid paper will be sticky taped to the burette and placed as close as possible to the flowing water. The same grid paper will be used and left at the same position throughout the experiment.
The experiment will be conducted in a room with all windows closed and air conditioning switched off to reduce effects atmospheric effects on the angle of deflection of the water.
The one person will be using the same stopwatch every time to reduce systematic errors.
The same piece of silk cloth (20 cm in length, 15cm in width) will be used throughout the experiment
The same two people, (person with stopwatch and person controlling the glass rod) will conduct the experiment to keep random errors in measurements and readings consistent.
Materials and Equipments List:
– 50 mL Burette
– 20cm x 15cm silk cloth
– 1cm diameter glass rod
– Distilled water
– 200 mL Beaker
– A4 Grid paper with increments of 1mm
– Protractor with increments of 0.5 degrees
– Retort Stand
– Sticky tape
– Stop watch
1. Attach the clamp to the retort stand.
2. Fill the burette with distilled water to approx 1cm from the top and attach it to the clamp
3. Draw a straight line on the grid paper with a ruler and sticky tape it to the bottom of the burette, lining up the line on the paper exactly with the flow of the water coming out of the burette.
4. Also Draw a line 90 degrees towards the line if the flowing water but stopping at 0.5 cm from the line. This line will be where the charged glass rod will be placed
5. Also mark the origin (the tip of the burette, where the water comes out) on the grid paper
6. Place the 200 mL beaker under the burette and let the water run down
7. Start the timer on the stopwatch and simultaneously, begin rubbing the glass rod against the piece of silk
8. Stop the stop watch at 10 seconds and immediately place the charged rod as close as possible to the line drawn on the grid paper
9. Mark the angle of deflection of the water on the grid paper
10. Wait 1 minute until the rod is completely uncharged
11. Repeat steps 6 – 9
12. Repeat the experiment from steps 6 – 10, changing the time rubbing the glass rod against the silk cloth by 20, 30, 40, 50 and 60 seconds.
13. Remove the grid paper and line up all the points of the deflected water to the origin
14. Measure the angles with a protractor and record the results into the table below
15. Pack up the experiment
Table 2 – Raw data table
Time charging the glass rod
Angle of deflection of water
Table 3 – Risks involved in the experiment and safety precautions to reduce the risks
Action to take
The burette is very long and is made of glass and can be broken easily
Hold the burette with two hands and always watch for obstacles when carrying around the lab. Wear closed in shoes, lab coat and safety glasses in case the burette breaks.
Carefully pick up the large pieces of broken glass one by one and throw in the glass bin. Use a brush to sweep all the small bits into the bin. Make sure there is no remaining broken glass in the lab.
1. Columbia University Press (1978-1979). New Illustrated Columbia Encyclopaedia
2. Neuss, Geoffrey (2007). Chemistry Course Companion. Oxford: Oxford University Press.
4. Department of Physics and Physical Science, University of Nebrasky, Kearney Falling Water http://rip.physics.unk.edu/CyberTextBook/fallingwater/