Apparatus: -
- Trough
- Delivery Tube
- Rubber Bung
- Boiling Tube
- Magnesium Ribbon
- Dilute Hydrochloric Acid (Concentrations 0.5, 1.0, 2.0)
- 10cm³ Measuring Tube
- 100cm³ Measuring Tube
- 5 25cm³ Beakers
- Stop clock
Diagram: -
Safety: -
Basis safety equipment must be used, such as a lab coat, wearing a hair band and using safety goggles to stop the dilute hydrochloric acid from getting onto the eyes or skin, and common sense, such as not to knock over beakers of acid.
Fair Test: -
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I will use the volume of dilute hydrochloric acid (20cm3) and the length of the magnesium (2.5cm) as the controls for this experiment.
- The magnesium will have to be cleaned, because it will have reacted with the oxygen in the air causing the outer layer to be oxidised and become magnesium oxide.
- We will pour in the dilute hydrochloric acid (the variable) before we add the magnesium. Also, we will hold magnesium against test tube and then careful let it drop quickly before we put on the rubber bung. This will prevent a loss of the product gas, hydrogen.
- Each experiment will be done until there are two results within 10% of each other, so an accurate average can be calculated.
- The volume of dilute hydrochloric acid will be measured using a beaker and then a measuring cylinder to increase accuracy.
PRELIMINARY EXPERIMENT
Method: -
The apparatus was set up as shown in the above diagram. The controls and variables were kept the same. The stop clock was started when the magnesium was added. After 10cm³ of gas was produced, the stop clock was stopped. The time was recorded and the experiment was repeated until there were 2 results within 10% of each other.
Results: -
Conclusion: -
My preliminary experiment was good; however it did raise some issues, which I will change for my actual experiment.
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I will keep the amount of gas to collect at 10cm3. I felt this was sufficient.
- I will also keep the range of concentrations I’m using the same. These are 0.5M, 0.75M, 1.0M, 1.5M and 2.0M.
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I will change the volume of acid to 20cm3 and I will change the length of the magnesium to 3.0cm as I feel the reaction for 2.0 M will be too fast for me to record reliable, accurate results
FINAL EXPERIMENT
Method: -
The trough was filled until it was three quarter full. Then the boiling tube was filled with the 20cm3 of hydrogen chloride and the rubber bung placed securely on the top of the boiling tube. The delivery tube was placed so that it lay on the bottom of the trough and so that the end was underneath the water. The measuring cylinder was filled to the 10cm3 and a hand placed over it so that no water spilled, and it was turned upside down. The measuring cylinder was then placed under the water with the hand still underneath, then the hand was removed. This was done to ensure that exactly 10cm3 of water remained in the cylinder. The measuring cylinder was then placed over the end of the delivery tube. The magnesium ribbons were all cut to exactly 2.5cm and one was placed inside the boiling tube. The stop clock was started precisely when the magnesium was added. Once 10cm3 of the gas had been produced, the stop clock was stopped immediately. The time was recorded and the experiment was repeated until there were 2 results within 10% of each other.
Results: -
Conclusion
My results show that the higher the concentration of dilute HCL acid, the shorter the amount time taken for 10cm3 of hydrogen to be produced, which means that the concentration is inversely proportional to the time taken. From my graphs and table of results I think that my prediction is partly correct, but the concentration is not directly proportional to rate of reaction. The graph shows a smooth curve and steady dencrease in the gradient of the curve. This and the table of results illustrates to me that the second part of my prediction is also correct. My second graph illustrates that the rate of reaction increase as the concentration increases.
Evaluation and Analysis
I think the experiment as very accurate as we planned a fair test and carried it out. Also, we only got one anomalous result. This was discounted and this molar was repeated. The experiment worked well because I had enough results to draw a reliable conclusion.
I did a preliminary experiment to see what would work and what I would have to do make my experiment more accurate and reliable.
I think the experiment used a good method as my results showed a smooth curve when plotted onto a graph. I would however improve it if had to repeat it.
I would use a thistle a gas syringe to collect the gas, which would give a more accurate reading. It was clear when to stop the stop clock as I was down at eye level and the measuring cylinder was easy to read. All my results were within 10% of each other, so I had no anomalous results.
I have proved that the concentration of dilute hydrochloric acid is inversely proportional to the concentration. My experiment was limited as I only investigate one acid and one metal, but I think that is reasonable to conclude that in a reaction with a metal and an acid, the higher the concentration of the acid, the higher the rate of reaction. I could redo the experiment I would experiment with more concentrations to improve the experiment, and also I would tie the magnesium to a piece of string and tilt the boiling tube in order to make sure that no gas escaped.
