CONCLUSION
I can conclude that if you double the concentration of the acid the reaction rate would
also double, this is because the ions are closer together in a concentrated solution. The
closer together they are, the more often the ions collide. The more often they collide, the
higher the chance of a reaction between the magnesium and the hydrochloric acid. Also
because there are more particles in the solution which would increase the likelihood that
they would hit the magnesium so the reaction rate would increase. The graph gives us a
good device to prove that if you double the concentration the rate of reaction doubles. If
you increase the number of particles in the solution it is more likely that they will collide
more often. In the reaction, when the magnesium hit the acid, it fizzed and produced
many bubbles it was silver in colour(which is one magnesiums physical properties silvery
white metallic element), the activation energy of a particle gets higher with heat, the
particles which have to have the activation energy are those particles which are moving,
in the case of magnesium and hydrochloric acid, it is the hydrochloric acid particles
which have to have the activation energy because they are the ones that are moving and
bombarding the magnesium particles to produce magnesium chloride. The graph for
1/time had the form of an s curve and it did have some relationship with the other graph.
EVALUATION
There are many reasons why our results for the 1/time graph did not prove the point that
concentration~1/time,such as
1)When the reaction takes place bubbles of H2 are given off ,which might stay around the
magnesium which therefore reduces the surface area of the magnesium and so the acid
cannot react properly so this effects the results.
2)We could have controlled factors in the investigation better (e.g the stirring of the
solution because if this is´nt done properly it can lead to incorrect results).
3)using larger concentrations of acid would give a bigger more accurate conclusion
instead of just using 10ml testubes use 1litre testubes, this way graphs would be more
spaced out and give an accurate form or curve
Marble Chips and Hydrochloric Acid Investigation
Aim: The aim of this investigation is to find out if altering the concentration of hydrochloric acid will have an effect on the rate of the reaction when marble chips are dissolved in hydrochloric acid.
Main Factors:
These are the main factors that will be taken into consideration when undertaking our investigation.
What affects the Rates of a Chemical Reaction?
This investigation is to investigate the rate of the reaction when marble chips are dissolved in various amounts of hydrochloric acid. In order for the investigation to be a fair test, all the variables except the concentration of acid should be kept constant. The investigation has to be done in a fair manor otherwise the results would be inaccurate and the conclusion would be incorrect. The variables, which must be kept constant, are:
- Temperature
When particles are heated they gain energy. Raising the temperature causes the particles to move around more often in a certain time, therefore increasing the number of collisions, in turn increasing the speed of the reaction.
To control and keep the temperature constant we will monitor it at stages throughout the experiment.
- Surface Area
By increasing the surface are a larger number of atoms are exposed and ready to react. A larger surface area provides a larger area for the atoms to react on, as a result increasing the speed of the reaction. Consequently, smaller particles of solids will react faster than larger ones.
In this experiment we will be using medium sized chips for the duration, as this is a constant variable.
- Particle Size
A larger particle size will have a larger surface area and therefore a larger area for the acid to react on. So, if the experiment contains different sized particles, then the reactions will be happening at varying speeds that will produce inconsistent results.
Medium sized particles will be used for this experiment.
- Catalyst
A catalyst is a substance that increases the rate of a chemical reaction within an experiment. Catalysts make it easier for the particle to react, but is chemically unchanged at the end of the experiment.
We will not be using a catalyst in this experiment.
The variable is:
- Concentration
In an increased concentration of acid, there will be a greater number of particles moving about in the same volume, thus increasing the chance of particles colliding and causing a reaction with the particles on the surface of the marble chips. Increasing the concentration of the acid will also increase the rate of the chemical reaction.
low concentration of acid doubled concentration of acid
In a doubled concentration of acid, the particles will be doubled, therefore increasing the number of successful collisions.
Basic Plan
This experiment will be set up as shown below in the ‘diagram of experiment’.
Diagram of Experiment
A beehive shelf will be submerged in a container of water, and then a
100cm³-measuring cylinder filled with water will be placed upside down over the hole of the beehive shelf. A clamp stand will be positioned next to the container, holding a boiling tube. A plastic tube will connect the boiling tube and the measuring cylinder, allowing the carbon dioxide given off, to be measured in the cylinder.
We will use different concentrations and volumes of hydrochloric acid to calculate the rate of the chemical reaction.
Pre Investigation
This pre investigation is to determine the volume of acid and the mass of marble chips that we are going to use in our experiment. We aim to discard any volumes, masses or amounts that are unsuitable to be tested for. For example, if the reaction becomes too fast or too slow.
We have decided to keep the mass and size of the marble chips constant throughout our pre investigation, as it will be easier to only have the two changing variables; the concentration and volume of the hydrochloric acid.
In this pre investigation we are going to focus on testing different volumes, of the weakest concentration of acid and of the strongest concentration of acid. This is because we will not have enough time to investigate every possible combination of volumes and concentrations.
5g of medium sized marble chips with 10cm³ of 0.25m hydrochloric acid
This table shows that 10cm³ of hydrochloric acid is an inappropriate volume to use as no reaction occurred. This is because there were not enough particles travelling at a fast enough speed to create enough collisions to induce a reaction.
5g of medium sized marble chips with 20cm³ of 0.25m hydrochloric acid
This table again shows that the volume and concentration of acid we have used are unsuitable, as no reaction has taken place within our 180 second limit. As a result, we will have to continue investigating different volumes and concentrations of hydrochloric acid.
5g of medium sized marble chips with 30cm³ of 0.25m hydrochloric acid
You can see from this table that using 30cm³ of 0.25m acid produces a fairly steady and constant reaction, making the results easy to record. The particles are reacting with enough energy to maintain this constant speed.
For the next stage of our pre investigation we will test 30cm³ of hydrochloric acid at the strongest concentration of 2m, to anticipate the speed at which the reaction will take place.
5g of medium sized marble chips with 30cm³ of 2m hydrochloric acid
From these results we can see that the reaction takes place quickly, within 50 seconds. We were unable to record any further results as the measuring cylinder we used was too small and so filled with the gas quickly. This is something that we will bear in mind during our investigation.
Conclusion of Pre Investigation
The results of our pre investigation show us that using 30cm³ of acid provides a steady reaction with whatever the concentration. Using a volume below this does not create a reaction within the allocated time and using a volume above 30cm³ reacts too quickly for us to record precisely. From this, we have decided that in our final experiment we will use a larger measuring cylinder of 250cm³, to allow the experiment to run to completion or for a longer period of time. This will allow us to record the results more accurately.
Detailed Plan
We will be using the acid concentrations of 0.25m, 0.5m, 1m, 1.5m and 2m. We will test each concentration three times, so that we can obtain accurate results. The third test of each concentration is to confirm that the previous results are correct, and from this we can calculate a precise average.
Controlling the Variables
1) Temperature
To control the temperature throughout the experiment, we will monitor the surrounding area to make sure there are no sudden changes.
2) Surface area and Particle Size
To ensure that the marble chips have an equal surface area throughout each experiment, we will be weighing an exact number of them to equal the mass of 5g. The number of marble chips will be kept constant for every experiment.
3) Catalyst
To control the catalyst in this experiment, we will not be using one.
The Collision Theory
All substances are made up of particles, which can either be atoms, ions or molecules. Before a chemical reaction can take place the particles must crash together and ‘collide’. The more collisions there are between particles at a given time, the faster the reaction will take place.
A larger number of particles provide a larger number of successful reactions.
In order for a reaction to take place, particles must collide with a minimum amount of energy called the ‘activation energy’ (Ea). During this stag, bonds are broken and reformed as products as indicated in the profile below:
This is an exothermic reaction.
Prediction
I predict that as the concentration of the hydrochloric acid increases, so to the rate of the chemical reaction. This is because as the concentration increases, a greater number of particles are travelling and colliding in the same volume of acid, which therefore increases the number of collisions between the acid and the marble chips consequently increasing the rate of the reaction.
I believe that if the concentration of acid is doubled then the rate of reaction will also double, in turn halving the time taken to complete the reaction.
As a final point, the time taken to produce the carbon dioxide is directly proportional to the rate of the chemical reaction.
Prediction of Expected Volume of Carbon Dioxide
CaCO (s) + 2HCl (aq) CaCl (aq) + CO (g) + H O
When Calcium Carbonate and Hydrochloric acid are reacted together, CO will be produced. We are able to calculate the amount of CO that will be formed after the completion of the experiment.
This is the calculation used to determine the amount of CO that will be produced, by the experiment.
Step 1
Firstly, we must work out how much Calcium Carbonate is equal to 1 mole.
CaCO = Ca C CO
40 + 12 + 16 + 16 + 16 = 100
Therefore, we know that 100g of Calcium Carbonate is equal to 1 mole. We also know that 1 mole of gas will always occupy the same volume. This volume is 22, 400cm³.
Step 2
We have calculated that:
100g of CaCO 22, 400cm³ of CO
In our experiment we will be using 5grams of marble chips and so we will need to calculate how much CO will be produced by using this amount.
Calculation
5/100 = 0.05 moles {
0.05 moles of Calcium Carbonate will also produce 0.05 moles of Carbon dioxide.
0.05m × 22, 400cm³ = 1120cm³ of Carbon dioxide
So, I now know that our experiment should produce 1120cm³ of Carbon dioxide.
Final Experiment
Aim:
The aim of this investigation is to find out if altering the concentration of hydrochloric acid will have an effect on the rate of the reaction when marble chips are dissolved in hydrochloric acid.
Equipment:
The equipment that we will be using is as follows:
- Clamp stand
- Clamp
- Boiling tube
- Plastic tube
- 250cm³ measuring cylinder
- Beehive shelf
- Container
Method:
As used in our pre investigation, we will be using 5g of medium sized marble chips. From our pre investigation we have learned that 30cm³ of hydrochloric acid is the most appropriate volume to use, as this will provide us with a steady and constant reaction.
We will be measuring the speed of the reaction by the volume of carbon dioxide released from the experiment. We will take the results every 10 seconds and read them from the measuring cylinder. Taking the results every 10 seconds will allow us to obtain an accurate set of results, which we can then input into a graph.
We are performing this experiment in groups, so that we can ensure that each aspect of the experiment is performed accurately. For example, if one person is timing the experiment and that same person has to record the results, then there will be a time delay as the person looks from the stopwatch to the measuring cylinder therefore, they will record the result inaccurately as it would be late.
In this experiment, we do not feel it necessary that we will need to exceed our 3 minute time limit as we think that three minutes will provide us with a suitable range of results, and also we will not have enough time in the lessons to continue the experiment any further.
It will be very important to keep the starting temperatures of the experiments the same as, the results could be affected by this. If one experiment starts at a higher temperature, then the particles will have more energy and therefore making the reaction faster.
After our experiment, we will plot a graph with the results of the volume of CO released every 10 seconds for three minutes. With these results we will then be able to calculate the rate of the chemical reaction for each different concentration.
Diagram of Circuit:
The experiment will be set up as shown below.
Analysis of Graph
Average Rate of Reaction Analysis
The graph showing the average rate of reaction confirms that our results are extremely accurate.
Below is a table showing the results of the line of best fit.
A pattern has occurred as to how much Carbon dioxide is released. 1 mole of acid released 0.98cm³ of CO and 2 moles released 1.99cm³ per second. This shows that as the concentration is doubled, so is the volume of the of CO released. The results show that the volume is virtually double at 2 moles, but it is not exact as although we did control the variables they still may have had a minor effect on the results.
We have one irregular result at 0.25 moles. It is the furthest away from the line of best fit and this may have been because it was the lowest concentration of acid. As a low concentration of acid has a smaller number of particles, there is a lower chance of successful collisions, which therefore results in a longer time for the reaction to start. Another point which was made clear by our graph, was that at 120 seconds, there were a wider range of results as the concentrations became lower. The slight differences in the surface area became more apparent because of this, as there were a smaller number of acid particles to react.
Conclusion
Our results show that if we double the concentration then the rate of the chemical reaction doubles. In order for a chemical reaction to advance then it has to collide with a minimum amount of energy, known as activation energy. If twice the number of particles are involved in a reaction then the probability of successful collisions occurring is then doubled.
Overall, our results proved to be accurate, and that an increase in the concentration of hydrochloric acid, increases the rate of the reaction which in turn decreases the time taken.
Evaluation
From our graph, we can see that the majority of the plots were placed exactly on the line of best fit, therefore showing that our investigation was accurate. However, we are only able to say that our investigation was accurate over the small range of acid concentrations that we tested.
Our results show that the speed of the reaction will increase when a higher concentration of hydrochloric acid is used. Comparing the results at 2 moles and at 0.25 moles, it is clear that the reaction took place much faster at 2 moles with 2.08cm³ of carbon dioxide produced per second, as appose to 0.05cm³ being produced where the concentration is 0.25m.
Our results have proved very accurate and could not be improved by a great deal. The accuracy was ensured in the way that we performed the experiments, as we tested each concentration three times to confirm the average result for each concentration of acid.
I believe that our results were probably most affected by the size of the marble chips that we used. Although they were labelled ‘medium’ sized and we measured as near as possible to the mass of 5g, a small range of particle sizes could have been, and were present. If some particles had a larger or smaller surface area then the speed of the reaction would either be increased or decreased accordingly. As the concentrations decreased the different sizes in the particle chips became more apparent, this was because there were a wider range of results, before we calculated the average. The size of the surface area had less of an effect on the higher concentrations of acid because the reaction was taking place so quickly and this was because if the marble chips had a slightly larger surface area, then there would have been a greater chance of successful collisions causing the reaction.
Another factor that may have slightly affected the accuracy of our results was that we did not use hydrochloric acid from the same bottle for each experiment. This may have caused slight variation in the results, as the concentrations may have varied a little.
Possible suggestions for ways to improve our experiment
- To improve our experiment we could have added the marble chips to the acid instead of pouring in the acid onto the marble chips. Doing it in the way we did, which was pouring the acid onto the marble, started the reaction before all of the acid was present and therefore gave an unfair advantage of starting the reaction early.
- Instead of performing the experiment in the way that we did, we could have used a balance and weighed the amount of mass that was lost during the experiment, rather than measuring the volume of the CO released.
- To measure the volume of carbon dioxide we could have used a gas syringe, which would have given us a more accurate reading of the volume, which in turn would make our results slightly more accurate.
- To ensure that the total surface area of the marble chips were exposed and available for reaction throughout the experiment, we could have used a magnetic stirrer, to stir the solution and make sure that the maximum available surface area was exposed.
To further this investigation we could experiment with other concentrations between our 0.25m and 2m boundaries. As these would give us a wider and more accurate set of results.