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Henry Lee 9C 2014

Chemistry Year 9 Term 2 Investigation

Question: Does the surface area of the magnesium strip affect the initial rate of reaction?

Hypothesis/Prediction: By increasing the surface area of the magnesium strip, the initial rate of reaction will increase as well.

Independent variable: The independent variable is the length of the magnesium strips.Dependent variable:This experiment will measure the amount of carbon dioxide produced.Controlled variables: Concentration of acid/M Amount of hydrochloric acid/50ml

Apparatus: Basin 100cm3 measuring cylinder 50cm3 measuring cylinder 100cm3 conical flask clamp stand bung with plastic tube magnesium strip (about 10 cm) sandpaper stopwatch about 300cm3 of hydrochloric acid (1.0M)

Method:1. Use the sandpaper to scrape off the coating from the magnesium strip.2. Cut the magnesium strips into 1cm, 2cm, 3cm, 4cm and 5cm long strips.3. Fill the basin to about with water.4. Fill the measuring cylinder to the brim with water.5. Flip the measuring cylinder upside-down and put the mouth of it under the surface of the water in the basin. Use the clamp and stand to keep the measuring cylinder in position.6. Pour 50cm3 of hydrochloric acid into the conical flask.7. Insert the tube end of the bung into the measuring cylinder.8. Drop the 1cm strip of magnesium into the hydrochloric acid and start timing. Remember to bung the conical flask as fast as possible. Measure how much water has been displaced every 10 seconds for 50 seconds.9. Repeat step 8 to measure the water displaced for the other magnesium strips. Ensure that all the controlled variables are reset as shown in steps 4, 5 and 6.

Diagram:

Table we will record the results in this tableLength of magnesium/cmWater displaced/ cm3Rate of reaction (at 20 sec)

10 sec20 sec30 sec40 sec50 sec

110151722280.75

211192934410.95

311233344521.15

416324862771.60

520405880952.00

Graph

Graph

Conclusion:Through this experiment, I can conclude that the outcome confirms my hypothesis that the length of the magnesium strips does affect the rate of reaction. The rates of reaction of the 1cm, 2cm, 3cm, 4cm and 5cm strips are 0.15, 0.95, 1.15, 1.60 and 2.00 respectively. As you can see, the results show that the rate of reaction increases when the length of the magnesium strip increases, thus proving that surface does affect the rate of reaction and also proving my hypothesis to be correct.

Evaluation:Our experiment was to measure the water displaced by the bubbling/fizzing magnesium and see if there was any connection between the surface area and the rate of reaction.Although the experiment itself went along without many major problems, my group did discover a few flaws in our method. Perhaps the biggest problem was the fact that our method was not a very fair test. By using different lengths of magnesium strip, we not only increased the surface area, but also increased the volume, giving us a systematic error. The addition of the increase of volume will produce unfair results, thus deeming them unreliable. A solution to this problem is to get 5 pieces of 5cm long magnesium strips, then cut them into equal parts e.g. one whole strip, a strip divided into 2, a strip divided into 3 etc. This would provide a much higher level of accuracy, thus making the data much more reliable.A few minor problems were brought up during the experiment. Due to the magnesium being coated in a protective coating, we had to scrape the coating off manually with sandpaper. Since our scraping is never fully consistent, it can cause a slight change in the results. We can use uncoated magnesium to ensure better and more accurate results. Another issue that was present was the fact the magnesium was not always fully submerged. The strips of magnesium would occasionally pop up to the surface and float on the top. This leads to the reaction happening on only one side. The rate of reaction is therefore slower due to a smaller surface area, as one whole side is not reacting. A solution to this problem would be to use a glass rod to push the magnesium strip down and keep it under the surface. Another problem, albeit less important, is the fact that the position of the tube connecting the conical flask to the measuring cylinder can change, therefore causing unfair results. By changing the position of the tube, it can get harder or easier for the bubbles to travel through the tube. We must make sure than the tube is in the approximately same position, for example it could be arching up or it could be arching down. One last issue is human accuracy. It can be quite hard to judge exactly how much water has been displaced at a specific time due to the rapidity of the displacement and also movement of your eye level. This issue is a random error and therefore cannot be fixed.

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