If I were going to take the concentration of the hydrochloric acid further approximately up to 3M I would expect to see again an increase in the curve of the graph.
As the brown line (3M) has steepened considerably, it shows that the greater the concentration used the faster the rate of the reaction. This is simply due to the fact that there are more particles able to collide with others in the solution, as there are a larger amount of particles which means there is a higher collision frequency and a fraction of these particles would posses the activation energy needed to break existing bonds between each particle and ultimately to form new bonds so therefore they are successful collisions and create a product.
Another name for a successful collision is a ‘fruitful collision’ this is explained further in the diagram showing how particles react whether successful or not:
As one of the products formed in this reaction is carbon dioxide, I will therefore measure the rate of it produced throughout the experiment by the amount of carbon dioxide given off at a certain time by collecting gaseous product in a syringe.
The reaction rate or rate of reaction for a reactant or product in a particular reaction is intuitively defined as how fast a reaction takes place. There are numerous ways a reaction can be influenced by certain factors of which some are listed and explained further below:
Concentration
Reaction rate increases with concentration, as described by the rate law (the rate equation is a differential equation, and it can be integrated in order to obtain an integrated rate equation that links concentrations of reactants or products with time).
It can elucidate further by the collision theory, which was explained prior to this. As a reactant concentration increases i.e. hydrochloric acid, the frequency of collision increases also. The diagram below shows a clear view of how concentration can affect the rate of reaction:
- In dilute acids such as the one in flask A, there are few acid particles; this means that there is a much smaller collision frequency this means that there is less chance of an acid particle colliding with the calcium carbonate molecule due to the concentration.
- In flask B the acid is much more concentrated (simply meaning that there are much more acid particles contained in it). There is now more chance of a successful collision-taking place, as there are more particles that contain the activation energy needed to form products by breaking bonds and form new ones.
As you can see from the graph on the left shows the relationship between concentration and time; it shows that the slope of the of the reaction curve decreases with time, this is due to all reactant particles being used up and the successful collisions have reached their optimum, I would expect to see such correlation within my graph.
The concentration of many substances is measured in its molarity (moles per litre). One mole is simply a number (6.022×1023), or one mole could also be described as the quantity of a substance whose mass (g) is identical to its atomic weight. Therefore, 1 mole of hydrochloric acid (ignoring the fact it’s dissolved in water) could be worked out by adding the atomic masses of hydrogen and chlorine to get 36.46. Therefore 36.46g of hydrogen chloride would be the same as 1 mole, and 1M of hydrochloric acid is 36.46g/l. The concentration will be the independent variable in my experiment, and I will be using hydrochloric acid with different molarities in order to see what effect the concentration has on the rate of reaction.
Temperature
Increasing the temperature increases reaction rates because of the disproportionately large increase in the number of high-energy collisions. It is only these collisions (possessing at least the activation energy for the reaction), which result in a reaction. The ‘Maxwell-Boltzmann Distribution’ above can explain this.
Temperature will be a control variable in the experiment. As I will need to increase the temperature for the reaction concerning calcium carbonate and hydrochloric acid as the room temperature will be adequate for the reaction to occur.
Surface area
If a solid reactant or a solid catalyst is broken down into smaller pieces the rate of reaction increases i.e. calcium carbonate.
The speed increase happens because smaller pieces of the equal mass of the solid have a greater surface area compared to larger pieces of the solid.
Therefore, there is more chance that a reactant particle will hit the solid surface and react ultimately causing a successful collision.
I will therefore keep the surface area of the reactants the same in my experiment.
Pressure
The rate of gaseous reactions increases with pressure, which is, in fact, equivalent to an increase in concentration of the gas.
However as there are no reactants that take the form of a gas therefore the affect of pressure on the rate of reaction will not apply to the reaction between hydrochloric acid and calcium carbonate.
Catalyst
The word catalyst means an added substance, in contact with the reactants, that changes the rate of a reaction without itself being chemically changed in the end.
Catalysts increase the rate of a reaction by helping break chemical bonds in reactant molecules and provide a 'different pathway' for the reaction.
This effectively means the Activation Energy is reduced; in this case it affects an exothermic reaction (even though it does affect both types of reaction) below is a diagram to show this:
I will not be using a catalyst in my experiment as they are usually used when one of the reactants is a gas, and that it will not in anyway help me achieve my aim.
Variables
Independent:
My input and independent variable will be the concentration of the hydrochloric acid, measured in Molars (M). I will have 6 different reactions using 0.5M, 1.0M, 1.5M, 2.0M, 2.5M, and 3.0M of acid for each one.
Dependant Variable:
My dependent variable will of course include the rate of reaction, as this is what I want to find out. However, the rate itself is calculated from dividing the volume of the gas given off, therefore making the volume of gas and the time taken to be dependant variables as well.
Control:
The control variables are those that need to be kept the same for a fair test. The control variables include temperature, as changes in temperature will directly result in a change in the rate of reaction. The mass of calcium carbonate and volume of hydrochloric acid must be kept the same for each reaction so the experiment is kept fair, as more particles of either reactant will affect the rate. I will use a top hand balance and measuring cylinder.
The surface area between the CaCO3 chips and the hydrochloric acid must be kept the same. I will ensure this works by roughly picking the same sized chips (“medium chips”) and using the same sized conical flask in each reaction.
The water contained in the conical flask after having done the experiments and been washed, we need be precautious in doing so as it may dilute the concentration of the hydrochloric acid, so for example, acid at 2M could be diluted slightly which could affect the accuracy of the results. In order to keep this variable controlled we must make sure that the conical flask is cleaned thoroughly after usage.
We could confirm that the gas attained via the experiment is carbon dioxide by examining whether limewater turns cloudy. If the water changes into a cloudy solution then carbon dioxide is the gas given off and vice versa.
Pre – test
In order to measure the rate of reaction I will now explain what I will do in the pretest. The aims of my pretest are:
- To identify any potential factors that I may need to control for the actual experiment.
- To select a range of concentrations and a suitable surface area of the calcium carbonate, this will provide the most accurate results in the time and equipment given.
I will measure the rate of reaction by measuring the volume of the carbon dioxide gas given off from the reaction. I will be conducting three different experiments in order to find out which experiment will be most useful when examining the rate of reaction. There are three experiments I will perform these being the following:
- Using a measuring cylinder to accumulate the amount of gas given off.
- Mass method.
- Collecting the gas in a syringe.
Method 1: using a measuring cylinder in order to accumulate the amount of gas give off
I will use the following method in order to see whether it would be a suitable method when gaining accurate results. I would set the apparatus out as shown below:
To conduct this experiment we had to collect the necessary equipment and set the apparatus up as shown. We must then add the medium sized marble chips measured at 2g to 15ml of hydrochloric acid and then quickly fasten the bong to the flask trying not to let any gas escape. We would then record the amount of gas given off every 10 seconds in a period of 2 minutes.
I have accomplished the experiment and I have came to a conclusion that it is not the most accurate method, as there are numerous factors which could affect the results obtained. One negative entity about using this method is the difficulty of recording the measurements; due to the numbers being transparent this makes it extremely difficult especially when recording the results in time.
Another reason for why this technique should not be used is due to its disorderliness, water is able to go everywhere in the workplace as the cylinder is placed upside down within the experiment. Furthermore gas can be lost through the measuring cylinder being tilted, and again through the start of the practical when placing the bong on the conical flask.
Below are the results I have collected from this method, I will now analyse these in order to give me an overall conclusion to whether or not choosing this method would be a wise decision.
As you can see from the results that there are no decimal points and furthermore we have not rounded up or down neither showing attaining accurate results is very difficult when using this method.
I will not be using this method due to its unreliability, for example the loss of gas and it not being a fair test; these were crucial to the experiment and should have not been affected in anyone as it simply destroys the purpose of conducting it.
Method 2: Mass method
An alternative way of finding how the rate of reaction is affected is to examine the mass as the experiment carries on, this again would tell us the amount of gas (carbon dioxide) being produced.
This method is undertaken by using a top pan balance to measure the amount of carbon dioxide given off in gaseous exchange through the loss of mass by the solution. I will use the apparatus as follows:
We first gathered the equipment and set it up as shown above, we then measured the mass of the solution at 0 minutes which was a total of 50g, We then continued the experiment for seven minutes, every one minute interval we measured the loss of mass from the solution.
Due to the results remaining too consistent throughout there was not much drastic change so we could not tell whether carbon dioxide was being released through gaseous exchange; showing that this method is also unreliable.
Furthermore this method took far too long when obtaining the results meaning the results could not be accurate as the collision frequency was evidently far too low as the rate of gas given off was too unreliable and waiting one minute only extended the actual experiment further. In addition to this the marble chips took a considerable amount of time to weigh which again prolonged the experiment and due to these reasons I will not be using this method due to its unreliability and the time consumption.
Method 3: Attaining gas through a syringe
This method concerns using only a syringe to collect the volume of gas produced i.e. carbon dioxide from the reaction taking place.
Evidently this method is more accurate then the rest especially when recording the results accurately, the readings are also measure in points that again improve the accuracy of the experiment and obtaining the results. In addition to this there is a lesser chance of the carbon dioxide escaping, only when securing the bong onto the conical flask would this cause a problem. Thus I will be conducting this experiment in order to see whether the concentration of hydrochloric acid affects the rate of reaction between it and calcium carbonate.
Equipment
I will be using the following apparatus in order to carry out this experiment:
- Syringe
- Conical flask
- Rubber tube
- Boss
- Clamp stand
- Stopwatch
- Clamp
- Measuring cylinder
- Top hand balance
- Pipettes
Safety
There are numerous safety regulations that need to be taken into consideration when conducting the experiment to ensure that I am safe and also other pupils around me. I will need to wear goggles at all times to reduce the risk of any reactant entering my eye i.e. hydrochloric acid. Furthermore I must be aware of fine dusts as they have a large surface area and the cause of friction could initiate the reaction. I must also avoid spill the acid onto my skin as this can cause irritation, and if it was to go on my clothes it could ultimately destroy the fabric. Obviously prime principals of safety such as putting stools under tables and not running in class all apply.
Plan
1) 20ml of hydrochloric acid will be added into the conical flask. The acid will be 0.5M. 2g of calcium carbonate medium sized chips will be put into the flask. The flask will be closed, and the stopwatch timer will be started.
2) The reaction will begin and the gas will move through the rubber tube.
3) The cylinder will be pushed along through the gaseous exchange. The volume of the gas will be measured when there is no visible reactant (calcium carbonate) or when there is no more fizzing. I will expect the quickest rate of reaction between the greatest concentration of acid and the CaCO3 powder, and the slowest rate of reaction between the large chips and the 0.5M of hydrochloric acid.
4) The tests will be repeated using the different concentrations of hydrochloric acid and different surface areas of the calcium carbonate. The calcium carbonate will be measured to the accuracy of 0.1g. The hydrochloric acid will be measured to the accuracy of 0.5g.
The volume of gas will be recorded to the nearest cm³. The time taken for the gas to be produced will be measured to the nearest second. The mean rate of reaction will be measured to 2 decimal places.
We will use the preliminary test in order to finalise the size of the marble chips we would use in order to obtain accurate results; so for example if the marble chips reacted to fast with the hydrochloric acid we would have to increase the surface area of the marble chips in order for us to achieve the investigation.
Pretest results
3M
0.5M
As you can clearly see from the graph that the higher the molarity the quicker the mean rate of reaction, though also the smaller the surface area the more rapid the rate of reaction. I have thus decided to use medium chips as it gives a clear average on the whole. In addition to this the small chips and powder would react too quickly with the hydrochloric acid especially when using a higher concentration of acid in the given space of time.
I have also decided to measure the rate of reaction within a minute due to the fact that
How to conduct a fair test within my experiment
It is essential within the experiment that each separate test should be kept as identical to the other as possible except when changing the independent variable i.e. the hydrochloric acid. Here are a few factors which should be kept under control to ensure a fair test is carried out:
- I must make sure that all dependant variables are kept the same such as gas pressure, temperature and the surface area of the calcium carbonate (2.0 g) in order to gain reliable results as each can influence the rate of reaction.
- Also make sure that the same measurement of acid is used with each different concentration i.e. 15.0 ml
- We must make sure that the same equipment is used during the experiment as it will take longer then one teaching period. As different equipment could affect the results gained.
- The reactants within the conical flask must not be shaken as this can increase the collision frequency and consequently speeding up the rate of reaction.
Results
Here are the results I have gathered after having accomplished my experiment, I have completed each 3 times in order to sustain accuracy and achieve an average.
O.5 molar
1.0 Molar
1.5 Molar
2.0 Molars
2.5 Molars
I have also compiled all the results into one large table in order to compare the results much more easily between each concentration; this is displayed on the next page.
Analysis
I have now constructed a graph showing the relationship between time and the amount of gas produced depending on the concentrations of the hydrochloric acid.
Similarities within the characteristics of each different molarity show that there are far more amounts of gas i.e. carbon dioxide given off at the start of the reaction than any other time. This is probably due to there being more acid particles available to react with calcium carbonate molecules, as each particle possess more energy at the start of the reaction thus there is a better chance of them acquiring the activation energy needed to break existing bonds to form new ones, which ultimately leads to creating products from this, thus can be shown in the graph created as there is a steep acceleration of the graph within all molarities. The steepest gradient was evidently from the 2.5 M this I had predicted from before hence the graph below. This is due to there being a greater concentration meaning there are more likely to be fruitful collisions as there are more likely to particles which posses the minimal energy required to break bonds. However the line expressing the 2.0 M starts off at a much slower pace then compared to the actual gradient of the line itself though this is probably due to a variable not being controlled properly, for example there could have been simply ‘dead volume’ within the syringe this is where there is already a little amount of pressure and could therefore extend the result measurements further then they actually should be.
However the steepest point on my graph actually derives from the 2.0M line not the 2.5 this being 90cm³/110s though this is probably due to the fact that the 2.5M decelerates before the latter, evidently meaning that because it has reacted so fast it slows down much more quicker than the 2.0M which still has few reactant particles waiting to turn into fruitful collisions.
My graph finally levels out at the later stages just after it has peaked to its highest gradient, this simply means that the chemical reaction has stopped occurring due to all the reactant particles being used up to form products, this can be seen as no more carbon dioxide is being produced from the reaction.
You can clearly see from the graph that the amount of products formed is clearly proportional to the amount of reactants used, this is shown by the steepness of the lines and how they increase as the molarity of the solution does as well. You can also see how the reaction stops through the results collected in my table for 2.5M; for 20 seconds consecutively the average remains at 92.6cm³ clearly indicating there are no more reactants left possessing activation energy. In conjunction to this the lines do no exactly create an evident constant line showing the reaction has actually stopped, therefore the experiment should be made longer possibly until the marble chip actually runs out.
From my graph I can also work out the reaction rate, for example if I was to work out the reaction rate for the 2.5M solution, after 2 minutes 92.6 cm³ is produced so the rate of the reaction = 92.6/120= 0.78/second.
From my graph and table results I state my hypothesis to be correct as the concentration of the acid clearly effects the rate of reaction. We can see this through the steepness of the gradient, the higher the concentration the higher the gradient, which in this case signals more gas is being produced, this is clearly because there is a vigorous chemical reaction taking place; in the solutions containing stronger acid there are patently more particles of the acid to react with the calcium carbonate molecules which effectively raises the collision frequency thus causing more fruitful collisions.
Evaluation
From observing my graph I concluded that a greater concentration of acid will result in a greater rate of reaction, which is what I predicted initially. However, when looking at the rate of reaction being proportional to the concentration of acid, it is slightly more difficult to obtain this evidence accurately from the graph, as it is not accurate to an adequate amount. This is because there could be numerous of reasons influencing the experiment.
Primarily as the reaction is exothermic this means that the temperature will steadily rise whilst the reaction continues, thus will have an effect on the rate of reaction. This would in turn cause inaccuracies with results, though the only way to maintain temperature at a consistent level would be for us to place it in a water bath which remained at a constant degree or for us to decrease the temperature as the reaction rate itself increased.
One major problem was the amount of time it took to place the bong securely over the neck of the conical flask. Although the delay was kept to a minimum, there is an exceedingly large chance that some of the gas could have been freed whilst the bong was being fastened. Therefore if I was to do this experiment again, I would use a method which would not actually involve the measurement of gases as this is an inaccurate method of measuring a rate of the reaction.
The syringe itself created many difficulties when carrying out the practical; this could again affect the results obtained. The friction between the inner and outer glass of the body could have made recording the actual results difficult.
The chips were created solely for the purpose of this experiment and therefore they are not identical, even though they are all categorized under the same name ‘medium chips’. They each possess different masses and even surface areas.
When inserting the acid through the syringe, the person who had completed the task before must do so again as different people are able to exert different pressures so this could increase the volume of gas produced. This may have explained why the 2.0M was at a steeper peak position than that of the 2.5M.
I think the anomalies in the experiments occur because of the measuring equipment being too inaccurate. While a measuring cylinder is only accurate to 0.5ml, and top hand balances is accurate to 0.1g which means that they are suitable for usage, there is no harm in using equipment accurate to 2 decimal places, this would have help me maintain accuracy when retrieving my results.
Extension
Aim
To see how the concentration will affect the rate of reaction by measuring the mass lost in a reaction.
Prediction
I believe that that the concentration will be proportional to the rate of reaction thus simply meaning that the loss of mass from the solution will be proportional to the concentration as well. This is evidently due to the collision theory, which is explained in my initial prediction. I have decided to improve the experiment from the preliminary tests in order to see whether I can improve its accuracy when obtaining the results.
Method
Equipment
-Marble chips (identical and possess same mass to ensure fairness)
-Hydrochloric acid (0.5M,1.0M,1.5M,2.0M, 2.5M and 3M)
-Stirring rod
-Stop clock
-Balance (accurate too 0.001g)
-Spatula
-Conical flasks
-Syringe
1. I will use a measuring cylinder and place 30ml of hydrochloric acid into a conical flask.
2. I will put the flask on the top hand balance accurate to 0.001g
3. I will then attain the mass of the conical flask and the marble chip and add them together (without adding the chip in the flask).
4. i will then put the marble chips into the flask and start the stop clock immediately.
5. The flask will be connected to the syringe yet again though this is primarily to try and look at the volume produced and the loss mass of the solution in order to be as accurate as we can.
6. I will take the readings of the balance every 15 seconds for 5 minutes, as I think this would be the time need in order for the whole chip to be consumed.
7. I will repeat the tests, but use a different concentration of hydrochloric acid.
Diagram:
Results table