In each case, the concentration of the catalyst will be kept constant and all other conditions such as temperature. The graph start off with differing gradients depends on the concentration of hydrogen peroxide I start with. Now I am in a position to answer the question “How does the rate of reaction depends on the concentrations of hydrogen peroxide ?”. I will plot the initial rate of reaction against concentration of hydrogen peroxide and I can arrive at the effect that it is a straight line graph.
This means that the rate of reaction is directly proportional to the concentration of hydrogen peroxide.
The theory behind my prediction is the Collision Theory
Enrgey distribution amongst molecules in a gas
Molecules have energy due to their motion. It is called Kinetic Energy. At any instant in time, some molecules have very high energies relative to the rest, because they are moving very fast, while other molecules have very low energies relative to the rest, because they are moving very slowly. Most molecules, however, have a range of energies between these extremes. The distribution of energies amongst molecules was calculated statistically by the Scots physicist James Clerk Maxwell in 1859, and more generally applied by the physicist Ludwig Edward Blotzmamm in 1871. The result is the Maxwell-Blotzmann distribution of molecular energies. Shows in Fig,27-.26.
The Maxwell-Blotzmann distribution explains why, at a particular concentration, only a certain number of collisions are affective ones, Fig.27.27 shows the effect of increasing concentration. At the higher concentration, a greater proportion of molecules have higher energies due to more collisions and so greater proportion posses’ energy equal to, or above, the activation energy, giving more effective collisions.
Name of book: Chemistry
Collins
Chris Connolly Advance
Phil Hills Science
Relating the theory to the rate equation.
I will fill the tube with water and then fill the measuring cylinder with water. After that I will fix the measuring cylinder on the stand. The opening of the measuring cylinder will be down side in the tub. Then I will put hydrogen peroxide with the pipette in the test tube. In the test tubes I will measure the hydrogen peroxide for 2ml, 4ml, 6ml, 8ml, and 10ml respectively. I will put the hydrogen peroxide with the pipette in the conical flask and then I measure the magnesium oxide to 0.2 g on the balance and put it in the conical flask, where the hydrogen peroxide is. Then I will put one end of the glass tube in the conical flask and the other end in the measuring cylinder at the same time I will start the stop watch. Then I start to count the volume of oxygen for 30s, 60s, 90s, 120s, 150s, 180s, and write them down.
Scientific reasons
Tub of water- oxygen is not soluble in water.
Measuring cylinder – easy to measure the volume of oxygen produced.
Conical flask – facilitate through mixing of reactants.
Stand - to fix the measuring cylinder firmly and upright.
Glass tube – if it is a rubber tube, it is very difficult to insert through the water and it will be blocked by the measuring cylinder pressing on it by its own weight.
Pipette – small volume of liquid could be transferred effectively.
Balance- to measure the weight accurately.
Test tube- small volume of liquids could be measured accurately.
Stop watch – to measure the time accurately.
The above comments are important because scientific experiments require accurate and precise measurements.
Risk assessment
Hydrogen peroxide: caution must be taken in handling hydrogen peroxide because it is irritative and burns the skin when it comes into contact with the skin.
The results of the preliminary experiment are as follows:
I did the experiment with different volumes of hydrogen peroxide. Then I did the actual experiment with the different concentration of hydrogen peroxide.
Obtaining evidence
I did the experiment as I planned and got the results as follows:
Analysing evidence and drawing conclusions
According to my experiment the rate of reaction increases as the concentration increases but not proportionally. That means, when I double the concentration there is no corresponding doubling of the rate of reaction. The theory behind this phenomenon is that the increase of the rate of reaction is due to more and more molecules being packed up in the same volume, as the concentration increases. This creating the chances of more collision resulting in the increase of the rate of reaction.
The curve drawn for 4mol /dm³ and 6 mol/dm³concentration some what deviated from the line of best fit. The readings at the concentration 10 Mol/dm³ are completely out of the prediction.
Evaluation
The results of my experiment fairly agree with the theory that as the concentration increases the rate of reaction increases. There was a complete error in recording the results at the 10 Mol/dm³ concentration.
My results were on the average expectation.
The results were not satisfactory. The curves were smooth not spacing out as that of the predicted graph.
I am not impressed by this method. I had difficulties at looking at the stop watch and at the same time noting the volume of hydrogen formed in the measuring cylinder.
Suggestion for improvement
To use a cork to close the opening of the conical flask. To make a hole in the cork and insert the glass tube so that it tightly fits around the tube. This is an improvement of the method there by facilitating the accurate measurement of the volume of oxygen produced.
The results were not reliable. It was unsatisfactory. I did not get the same results for each experiment. The results were not in an orderly manner. The readings of the volumes of oxygen produced were not proportionally increasing to varying concentrations of hydrogen peroxide for the constant time interval for eg: 30s, 60s, etc.
My results were not fully backed up by my conclusion. The results of the were not fully supporting the theory which states, that the rate of reaction increases proportionally to the increasing concentration of reactants.
The course for the anomalies may be due to the following reason.
- I have not put the cork on the opening of conical flask and not inserted the glass tube through the cork. Therefore there was a gap between the tube and the opening of the conical flask. Part of the oxygen would have leaked out of the conical flask instead of going through the tube in to the cylinder.
2) There was no co-ordination between the volume of oxygen produced and
noting the time at the stop watch.
3) There would have been possibilities of not taking the exact quantities in
Millilitre of hydrogen peroxide, when taking with pipette.
Another way of testing the prediction
The tip of the syringe (tube) is inserted through the hole in the cork, so that it tightly fit into the cork. First add 8ml water in the conical flask and then add 2ml of hydrogen peroxide. Both with the help of the pipette. Then magnesium oxide is added to the conical flask. The conical flask is closed by the cork carrying the syringe. The volume of oxygen produced can be measured for the time intervals of 30s, 60s, 90s, 120s, 150s, 180s. the concentration could be varied according to the following schedule.