rate of reaction

Magnesium + Hydrochloric acid = Magnesium Chloride + Hydrogen

     Mg (s)   +         2HCl (aq)         =             MgCl2 (l)       +      H2 (g)

Prediction

I predict that the higher the concentration of the acid the faster the reaction will take place. For a reaction to take place between different particles they need to collide with a sufficient amount of energy. The more times the molecules collide and react successfully the faster the reaction takes place. There are certain factors which improve this likelihood of a successful collision; they are temperature, chemical catalysts, surface area and concentration. Concentration speeds up the rate of reaction by having more molecules of a substance in a unit volume, e.g. a 2 molar acid will have more molecules of the acid then a 1 molar acid. To make this a fair test I will only change the concentration and will keep all other variables the same. Since I am using an acid I will take all the necessary precautions to avoid any accidental spillage or other forms of contacts with the acid. If I accidentally spill any acid on my body I will immediately wash it off with cold water

Preliminary Apparatus

1. 9x Magnesium Ribbon (11cm long)
2. 225ml of 1 molar Hydrochloric acid (75ml’s of 1 molar acid, 75 ml’s of 1.5 molar acid and 75 ml’s of 2 molar acid
3. 3x Conical Flask
4. 3x Bung
5. 3x Delivery Tube
6. 3x Measuring Cylinder
7. Stopwatch
8. Water-bath at 40°C
9. Ice bucket
10. 3x Thermometers
11. Water Trough

Preliminary Method

1. Measure 25 cm³ of 1, 1.5 and 2 molar hydrochloric acid and pour it into a conical flask.

1. Fix delivery tube onto the top of the bung.
2. Fill the water trough ¾ full with water.
3. Fill a measuring cylinder full of water removing all pockets and bubbles of air, then place the measuring cylinder under the water in the water trough making sure there is no air in the cylinder as it will affect the results of the experiment.
4. Drop an 11cm strip of magnesium ribbon into the conical flask with the acid inside.
5. Cover the conical flask with the bung and delivery tube on top of it and record the time it takes for the reactants to react and produce 20, 40, 60, 80 and 100cm³ of hydrogen.
6. Repeat the experiment three times for each different concentration of acid.        

Preliminary Fair Test

To keep my test fair I will use the same amount of all three acids and the same measurements of magnesium ribbon to achieve a correct set of results. I will also operate my practical at room temperature 26ºC (at the time of the experiment). Also I will use the same amount of water in the trough to not alter my results. I will be using the same type of bung, measuring cylinder delivery tube and conical flask.

Diagram

Results

Graph

        The graph shows that for example the time taken to produce 100cm³ of hydrogen is 20seconds for the 2 molar solution, 1.5 molar it took 24seconds and 59 seconds for the 1 molar solution.

Preliminary Analysis

My preliminary experiment went very well producing one minor anomaly which was at 1.5 moles where it took a lot quicker to achieve 100cm³ than I predicted which I think at the time was due to the area I was working in. I was working near the heaters giving the particles in the 1.5 mole experiment more kinetic energy increasing the rate of reaction decreasing the time it takes to achieve 100cm³ of hydrogen.

Preliminary Conclusion 

        

        My experiment worked very well but I need to add a few things into my method and apparatus. My method requires two people to conduct the experiment to ensure we get the most accurate results. The time it takes to drop the magnesium in the conical flask and put the bung on top is too long therefore altering the results. Also I forgot certain safety precautions such as goggles, gloves and an apron to protect myself from any splashes or spillages of acid.

Having completed my preliminary testing I then carried out the investigation to find out the affect of concentration to the rate of reaction.

Apparatus

1. 9x Magnesium Ribbon (11cm long)
2. 225ml of 1 molar Hydrochloric acid (75ml’s of 1 molar acid, 75 ml’s of 1.5 molar acid and 75 ml’s of 2 molar acid
3. 3x Conical Flask
4. 3x Bung
5. 3x Delivery Tube
6. 3x Measuring Cylinder
7. Stopwatch
8. Water-bath at 40°C
9. Ice bucket
10. 3x Thermometers
11. Water Trough
12. 1x Goggles
13. 2x Gloves
14. 1x Apron

Method

1. Put on goggles, gloves and apron.
2. Measure 25 cm³ of 1, 1.5 and 2 molar hydrochloric acid and pour each measurement into a separate conical flask.
3. Fix delivery tube onto the top of the bung.
4. Fill the water trough ¾ full with water.
5. Fill a measuring cylinder full of water removing all pockets and bubbles of air, then place the measuring cylinder under the water in the water trough making sure there is no air in the cylinder as it will affect the results of the experiment.
6. Drop an 11cm strip of magnesium ribbon into the conical flask with the acid inside.
7. Immediately cover the conical flask with the bung and delivery tube on top of it and record the time it takes for the reactants to react and produce 20, 40, 60, 80 and 100cm³ of hydrogen.
8. Repeat the experiment three times for each different concentration of acid.        

Results

Graphs

Average Results

Conclusion

        As I have stated in my prediction my results prove that the rate of reaction increases with the concentration of the acid. I find most of the points are on a steady curve upwards. I improved the accuracy of my experiment by taking three readings for every concentration and taking the average values. I made sure that I tried my best to ensure that all the variables except the concentration where kept the same. I made sure the bung was fixed tight to ensure that none of the hydrogen gas produced during the reaction was lost. I made sure I used the correct protective equipment to ensure my safety.

Evaluation

        I am quite satisfied that I carried out the investigation properly as a result of which the graphs prove my original prediction. I noticed that because the reaction between hydrochloric acid and magnesium wash exothermic the temperature of the acid went up. Since the temperature can also affect the rate of reaction if I had the opportunity I would like to investigate whether this increase in temperature affected the rate of reaction. I feel that in addition to measuring out the magnesium ribbon by its length I should have also kept a record of the actual weight of the ribbon to ensure that I was always using the same amount of magnesium.