To investigate the effect of concentration on the rate of a reaction - Magnesium + Hydrochloric Acid ---> Magnesium Chloride + Hydrogen.

Diagram

Results

Concentration: 1mole

50cm3 HCl : 0cm3 H2O

Concentration: 0.8mole

40cm3 HCl : 10cm3 H2O

Concentration: 0.6mole

30cm3 HCl : 20cm3 H2O

Concentration: 0.4mole

20cm3 HCl : 30cm3 H2O

Concentration: 0.2mole

10cm3 HCl : 40cm3 H2O

Key Variables

There are 4 main variables that will effect our experiment, these variables are:

• Volume
• Concentration
• Surface Area
• Temperature

These variables are kept under control in our experiment.

• Volume is kept at a constant of 50cm³.
• Concentration will vary.  See table on first page (it will go from 1m to 0.2m).
• Surface area of the Magnesium is kept constant  by making sure that we prepare the magnesium the same for each experiment (coiling it up) and we will use magnesium ribbon only.
• Temperature will be kept roughly the same(room temperature).  To improve our experiment we could use a water bath to keep temperature the same.  The same amount of heat will be produced in this experiment as our preliminary experiment but there is much less effect as we have used 30cm3 more of the solution.  Hotter the atoms, the more they vibrate, they more they collide, this could therefore effect the rate on certain experiments if the temperature is not kept constant.

Blank results table

Gradient Results Table

Analysis of Graph

The graph is made up of several curves which start at the origin.  This tells us that the volume of gas produced is not directly proportional to time.  Here is a summary of what our graph shows:

• The points make an obvious pattern.
• The graph shows that volume of gas produced increases as time goes by.

From the graph we can see one or two very small anomalies but they are not off by much.  This is very much due to the apparatus and procedure methods.  Using more accurate equipment (scales which measure the magnesium to a greater accuracy) and taking more care when preparing the experiment could reduce these anomalies.  By altering our method and using more accurate methods of cutting up the magnesium and rolling up the magnesium carefully so that the surface area exposed is the same we could have more reliable results.   The exact sources of error are mentioned below in my Evaluation.

Conclusion

From our results, and more clearly our graph, we can see that the rate of reaction changes with concentration. The higher the concentration of Hydrochloric Acid the faster the rate of reaction. This is because increasing the concentration of the reactants increases the number of collisions between particles and, therefore, increases the rate of reaction (as stated in my prediction).

Our graph shows a clear trend in the data, it clearly shows us that volume of the gas is not directly proportional to time (we can tell this because it is not a straight line graph).  The two graphs produced are curves and not straight lines.

From this experiment we have learned that this is a Exothermic reaction meaning it gives off heat.  This caused in problem in the experiment if we did not use a large amount of the solution.  The reason for this being that; when you increase the temperature of the molecules you will increase the proportion of molecules with the required Activation Energy.  This will cause more successful collisions, thus causing the rate of reaction to increase.

When doing the experiment I stated that it was important to keep temperature at a constant because of this reason.  To do so I used more of the solution so that the heat given off would not have a high enough temperature to affect the larger amount of solution.

Evaluation

• Curve of best fit on the graph fits the data very well.
• Sources of error in the procedure could have been due to:

1. Varying length of magnesium (human error)
2. The concentrations were slightly off due to bad measurements with the pipette.
3. The balance is accurate to 0.01g so it is unlikely that this will have caused any noticeable errors.

• The sources of error are due to apparatus used and human error.  Using more accurate equipment (scales which measure the magnesium to a greater accuracy) and taking more care when preparing the experiment could reduce these anomalies.  
• By altering our method and using more accurate methods of cutting up the magnesium, and rolling up the magnesium carefully so that the surface area exposed is the same we could have more reliable results.
• The data is very trustworthy due to the fact that we took two readings.  The likely hood of error decreases as we take more readings.  The average of the readings that matched closest was taken to ensure that our results were even more precise.

• Our preliminary experiment data and graph also backs up our results.
• My prediction

“I believe that the higher the concentration, the faster the rate of reaction” was correct and has proven successful.