The aim of this investigation is to determine whether if changing the concentration of a solution (hydrochloric acid) will affect the rate of which the reaction it occurs with another reactant (calcium carbonate). To do this I will need to research what t
How Concentration Affects
The Rate of a Reaction
The aim of this investigation is to determine whether if changing the concentration of a solution (hydrochloric acid) will affect the rate of which the reaction it occurs with another reactant (calcium carbonate). To do this I will need to research what the rate of a reaction is, the "collision theory", "activation energy" and the factors that affect the rate of a reaction. Also I will carry out a series of preliminary tests in preparation for my investigation.
A reaction can only take place when a successful collision is occurred, so for a reaction to take place two different elements have to concur with each other, this depends on the amount of atoms and energy in the two elements, this is called a successful collision. A chemical reaction can only take place when two different elements collide with each other.
What is the Rate of a Reaction?
The rate of a reaction is how quickly the product(s) are made or how quickly the reactants are lost.
Reactant (what we start with) ? Products (what we end up with)
The Collision Theory
For a chemical reaction to occur "successful" collisions need to take place. A successful collision is where the molecules that collide are the right way around, and collide with enough energy for bonds to break. If the collisions that occurred didn't happen the right way round or with out enough energy then they would simply bounce off each other.
Activation Energy
Even if the molecules are orientated properly, you still won't get a reaction unless the particles collide with a certain minimum amount of energy called the activation energy of the reaction. Reactants that have too much energy bounce straight off each other so a reaction will not occur. Reactants with not enough energy when collided won't have enough energy for a reaction to take place. Activation energy is the minimum amount of energy required before a reaction can occur.
If the particles collide with less energy than the activation energy, nothing important happens, they bounce apart. You can think of the activation energy as a barrier to the reaction. Only those collisions which have energies equal to or greater than the activation energy result in a reaction.
The Effect of Surface Area on Reaction Rates
You are only going to get a reaction if the particles in the gas or liquid collide with the particles in the solid, increasing the surface area of the solid increases the chances of collision taking place.
The more finely divided the solid is, the faster the reaction happens as the contact area is larger. A powdered solid will produce a faster reaction than if the same mass is present as a single lump. The powdered solid has a greater surface area than the single lump. When increasing the contact area, it allows for there to be more collisions per second, increasing the number of collisions per second increases the rate of reaction.
The Effect of Concentration on Reaction Rates
In 20mls of a low concentrated solution the volume is the same as in 20mls of a highly concentrated solution. The difference is that in the lower concentration the particles are more diluted than the particles in the higher concentrated solution. This is because in high concentrations the particles are crowed together and will collide with each other more often, resulting in an increased number of successful collisions. In low concentrations the particles are spread out and will collide with each other less often resulting in less successful collisions.
If the concentration is higher, the chances of collision are greater. This is because the numbers of collisions that occur are greater than those in a low concentration. The more frequent collisions there are the faster the rate of the reaction is.
The Effect of Temperature on Reaction Rates
Particles can only react when they collide. If you heat a substance, the particles move faster and so collide more frequently. By heating the particles, you will raise the energy levels of the molecules involved in the reaction. In a situation where the reaction is cold the particles are moving quite slowly, the particles will collide but with less force, and less collisions will be successful. Increasing temperature means the molecules move faster and the particles will collide with each other more frequently, with greater power, and more collisions will be successful, this will speed up the rate of reaction.
The Effect of Catalysts on Reaction Rates
A catalyst is a substance which speeds up a reaction, but is chemically unchanged at the end of the reaction. When the reaction has finished, you would have exactly the same mass of catalyst as you had at the beginning.
A catalyst provides an alternative route for the reaction to take. That alternative route has lower activation energy. A catalyst does not lower the activation energy; it provides an easier route for molecules to react. If the particles collide with enough energy they can still react in exactly ...
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The Effect of Catalysts on Reaction Rates
A catalyst is a substance which speeds up a reaction, but is chemically unchanged at the end of the reaction. When the reaction has finished, you would have exactly the same mass of catalyst as you had at the beginning.
A catalyst provides an alternative route for the reaction to take. That alternative route has lower activation energy. A catalyst does not lower the activation energy; it provides an easier route for molecules to react. If the particles collide with enough energy they can still react in exactly the same way as if the catalyst wasn't there. It is simply that the majority of particles will react via the easier catalysed route.
The Effect of Pressure on Reaction Rates
Increasing the pressure on a reaction involving reacting gases increases the rate of reaction. Changing the pressure on a reaction which involves only solids or liquids has no effect on the rate.
Increasing the pressure of a gas is exactly the same as increasing its concentration. If you have a given mass of gas, the way you increase its pressure is to squeeze it into a smaller volume. If you have the same mass in a smaller volume, then its concentration is higher. By increasing the pressure, you squeeze the molecules together so you will increase the frequency of collisions between them, the more collisions the faster the reaction will be.
So What Now?
Now that I know what the rate of a reaction is and I know what can affect it, I need to follow through my aim and investigate. I want to know whether if changing the concentration of a solution will affect the rate of a reaction, so first of all I need to choose the most suitable type (size) of calcium carbonate to use. To do this I will need to carry out some preliminary tests on different sizes of calcium carbonate to find out which size is most suitable to use. To be most suitable the size of the calcium carbonate should allow me to carry out my investigation quickly so that when recording my results it doesn't become time consuming or boring. Also it shouldn't be too quick, so quick that I am unable to record the results accurately.
Once I've a chosen a suitable size of calcium carbonate I can begin my investigation. If my changing variable is concentration, I need to choose enough different strengths and test each strength three times using the same volume of acid each time. I will be reacting the calcium carbonate with five different molars of hydrochloric acid. They will be at theses strengths: 0.1%, 0.5%, 1%, 1.5% and 2%. This is so when I am analysing the results I have a series of results to calculate averages from so that I can analyse them and determine a reliable and precise conclusion.
The equation for this investigation:
Calcium Carbonate + Hydrochloric Acid ? Calcium Chloride + Water + Carbon Dioxide
Ca Co³ + Hcl ? CaCl ² + H²O + CO²
To calculate the rate of reaction I will measure the Volume of gas produced (CO²) - using a gas syringe to measure the volume of gas given off. I will record the change in volume of the product per 20 seconds until the reaction comes to a complete end or at a set time:
rate = change in volume of product / time
Preliminary Work
For this initial study I will be testing three different sizes of calcium carbonate to find out which size is best to use in my investigation. The size of the calcium carbonate that allows me to record my results accurately and in good time will be used in my main investigation. I will be testing chunks (small surface area), chips (medium surface area) and Powder (large surface area). Each size of calcium carbonate will be recorded at 20 second intervals until the gas syringe can no longer collected the gas produced from the reaction or at a respectable time if the reaction takes a long time to come to an end.
Equipment
*
* Calcium Carbonate chunks
* Calcium Carbonate chips
* Calcium Carbonate powder
* Dilute Hydrochloric acid
* Conical flask
* Rubber tubing
* Bung
* Gas Syringe
* Stand
* Clamp
* Measuring cylinder
* Electronic scales
Method
* Set up equipment to diagram ?
* Measure out 10cm³ of Hydrochloric Acid
* Weigh chips of Calcium Carbonate exact to 0.2g
* Put the chips into the conical flask
* Pour in the acid and seal with the bung attached to the gas syringe
* Every 20 seconds record the readings on the syringe
* Continue until experiment stops or until a set time
* Repeat the above process for the calcium carbonate powder and chunks.
Results
Type of Calcium Carbonate
Reaction with Hydrochloric Acid
Large surface area (powder)
Reaction occurred very quickly.
Fizzed very vigorously and powder was dissolved very quickly.
Reaction had stopped in a matter of seconds.
Medium surface area (chips)
Reaction fizzed and the chunks dissolved after a few minutes.
Took longer than the powder but much quicker than the chunks.
Small surface area (chunks)
Reaction occurred very slowly.
Not much of a reaction only a little fizzing.
Chunks took a long time to dissolve over 20 minutes.
Analysis/Conclusion
Looking at my results I can see that the powder took the least amount of time for the reaction to occur, the reaction for this surface area happened very quickly and the reaction ended in a short amount of time.
The chips took a few minutes to come to a complete end. The reaction took longer than the powder but no where near as long as it took the chunks to react.
The chunks took a very long time to react; the reaction did not come to a complete end in the time I used to carry out this test and may have even taken 1 - 2 hours to complete fully. This surface area was time consuming to test and would not be suitable to use in my investigation.
After carrying out the preliminary work I found that the chips of calcium carbonate will be best to use in my investigation. This is because it will allow the reaction to take place at a decent pace, not too quickly so that when recording the results it would be difficult and inaccurate. Nor does it occur too slowly so that the investigation becomes time consuming and tiresome.
Prediction
As I have learned previously in my research the greater the concentration the faster the rate of reaction will be. I believe this to be true to my investigation. From this I predict that the higher the concentration is the faster the rate of reaction will be. The more molecules there are in the hydrochloric acid solution the more molecules there are to react with the calcium carbonate. So logically the higher the concentration is the faster the rate of the reaction will be. Also I predict that the 2% concentration of the hydrochloric acid will produce the fastest rate of reaction and produce the most CO². This is because this is the strongest of the five concentrations, being the strongest concentration it will have the highest number hydrochloric acid molecules in the solution to react with the calcium carbonate. Because there are many molecules to react with the calcium carbonate, more reactions will take place, the more reactions that take place the faster the reaction will be. Also the more reactions that take place the more CO² should be produced. This is because more calcium carbonate is reacting with the acid thus producing more CO². The more reactants react the more product is produced.
Safety and Fair Testing
Safety is especially important when handling harmful substances such
as Acid. Some accidents involving harmful substances, such as acids,
can cause permanent injuries such as damaged eyesight this is why it is compulsory that you take major safety precautions; this includes wearing safety goggles, tying hair back out of the way and over safety wear that may be available.
For this investigation I will be changing the concentration of the Hydrochloric Acid because this is the factor that I am studying, this will be my independent variable.
My dependant variables (other factors that can affect the rate of reaction) are:
* The temperature in which the experiment takes place,
* The surface area of the Calcium Carbonate
* The volume of Hydrochloric Acid used.
As these are factors that can affect the rate of reaction, I will need to make sure that they are kept constant throughout the investigation. This is to ensure that when the experiment is carried out, it is completed as fairly as possible and the results gained will be as accurate as possible.
Conical flask
Measuring cylinder
Scrap paper
Calcium Carbonate (chips)
Boss
Hydrochloric Acid
Electronic scale
Bung
Rubber Tubing
Gas syringe
Clamp
Stand
Equipment
NA
Exact measurements
NA
NA
NA
NA
Exact amounts
Air tight
Air tight
Exact readings of
gas collected
NA
NA
Accuracy
To host the reaction between the acid and the calcium carbonate chips
To measure 10cm³ of acid
To transport chips from scales to conical flask
Solid reactant
NA
Liquid reactant
To weigh the chips so they come to 0.2g
To seal tubing to conical flask
To connect the gas syringe to the conical flask via bung, providing a channel for the gas to travel through
To keep a record of how much gas collected at each interval
To affix Gas syringe to stand
To hold Gas syringe at eye level
Why?
Method
* Set up equipment to diagram ?
* Measure out 10cm³ of Hydrochloric Acid
* Weigh chips of Calcium Carbonate exact to 0.2g
* Put the chips into the conical flask
* Pour in the acid and seal with the bung attached to the gas syringe
* Stir continuously
* Every 20 seconds record the readings on the syringe
* Continue until experiment stops or until a set time
* Repeat the above process for each concentration of Hydrochloric Acid
Analysis
After carrying out the investigation I have found that there is a relationship between the concentration of a solution (in this case hydrochloric acid) and the rate of which the reaction it occurs with another reactant (calcium carbonate).
If you look at the line for the 0.1% solution of hydrochloric acid, you can see that the amount of CO² produced rises slowly and steadily until 380 seconds. From here onwards you can see that the amount of CO² produced seems to level off at 26.67cm³ indicating that it has come to an end. On average the rate of reaction is roughly 0.0860cm³ per second or 0.8608cm³ per 10 seconds. I worked this out by using the first two minutes (120 seconds) of the reaction and divided it by the amount of CO² produced (10.33cm³) in this amount of time. The total amount of CO² produced was 26.67cm³.
The plotted line for the 0.50 % concentration shows that for this percentage, the reaction that occurred was faster than the reaction that occurred for the 0.10 % concentration. This is shown visually as the line for the 0.05 % rises above the line for the 0.10 % concentration and is steeper which indicates a faster rate of reaction. Also this concentration has a greater total amount of CO² produced at 44.33cm³. The rate of this reaction is 0.09725cm³ per second or 0.9725cm³ per 10 seconds. I calculated this using the same method as I did for the 0.1% concentration. At the 440 second point the amount of CO² produced jumped up by 4.33cm³ from 35.67cm³ to 40.00cm³. This is a considerable rise in CO², from the 440 second mark until the 500 second mark the amount of CO² produced rises slowly and steadily but at the 500 second mark the amount of CO² produced jumps up again by 2.33cm³ from 42.00cm³ to 44.33cm³. The reaction for this concentration ended at 520 seconds, from this point onwards there was no more change in the amount of CO² produced.
The rate of reaction for the 1% concentration is 0.1667cm³ per second or 1.6667cm³ per 10 seconds. This was worked out the same way as I have worked out the previous rates of reaction. This rate of reaction is faster than both the 0.1% and the 0.5% concentration, you can also see this visually as the line of best fit for this concentration is steeper and rises above the 0.1% and the 0.5% concentration. The amount of CO² produced rises steadily until 440 second mark, here the amount of CO² produced rise considerably by 5.34cm³ from 38.33cm³ to 43.67cm³. Then it continues to rise at a steady pace until the reaction ends which is at 560 seconds and a volume of 47cm³ of CO² produced. You can see that reaction has ended here as the amount of CO² produced no longer rises. The total amount of CO² produced for this concentration is 47cm³.
When looking at the graph you can clearly see that for the line of best fit for the 1.5% concentration in the first 120 seconds the rate of reaction is faster than the 0.1%, 0.5% and 1% concentrations. This is shown by the line of best fit as it is steeper and clearly rises above the three previous concentrations. The rate of this reaction is 0.14167cm³ per second or 1.4167 per 10 seconds. This was calculated the same way as the previous rates of reactions have been calculated. You can see that the amount of CO² produced rises at a good pace until the time of 560 seconds and a volume of 60.33cm³ of CO² collected. You can tell that at this point the reaction has ended as no more CO² is being produced thus being that 60.33cm³ is the total volume of Co² collected.
The line of best fit for the highest concentration investigated (2%) shows that this concentration has the fastest rate of reaction of the five concentrations tested. You can see this illustrated on the graph as the line of best fit is much steeper than the other concentrations. The rate of this reaction is 0.205583cm³ per second or 2.05583cm³ per 10 seconds. This is the fastest rate of reaction compared to the 0.1%, 0.5%, 1% and 1.5% concentrations. The amount of CO² produced rises steadily until a time of 480 seconds. At this point the line for this concentration overlaps and drops just below the line of best fit for the 1.5% concentration. Also the total amount of CO² collected (59.67cm³) is lees than the total for the 1.5% concentration (60.33cm³). This is something that I had not expected. Being the highest concentration I thought that it will produce the most CO² and have the fastest rate of reaction.
Evaluation
For this investigation I obtained the results when carrying out the testing, at 20 second intervals I recorded the amount of CO² produced. I did this for each concentration and also tested each concentration three times to collect a series of results and to enable me to work out averages for each interval.
As I predicted when increasing the concentration of the Hydrochloric Acid the rate of the reaction also increase and that the 2% concentration of the acid produced the fastest rate of reaction. Looking at the data I plotted I can see that four out of the five concentrations tested agree with what I predicted. I predicted that the higher the concentration is the faster the rate of reaction will be. This is because the more molecules there are in the hydrochloric acid solution the more molecules there are to react with the calcium carbonate. The more reactions there are then the more reactions will be successful. The more successful reactions there are the faster the reaction will be. This was true for the concentrations 0.1%, 0.5%, 1% and 1.5%. Though the highest concentration (2%) did have the fastest rate of reaction but didn't produce the most CO².
A possible reason for this finding may be that the gas syringe may not have been sufficiently lubricated. If not properly lubricated friction could arise between the outer and inner pieces of the gas syringe. The CO² produced may not be strong enough to push past it, therefore producing inaccurate results.
Another reason may be that at this time in the testing period the conical flask may have been stationary instead of being stirred. This may have had an effect on the results obtained as shaking the flask has the same effect as increasing the temperature. The movement makes the particles collide more often so if they are not colliding as often the reaction may slow down.
When carrying out the investigation I felt that the whole process went well and was successful. Though there was one minor setback, a difficulty when weighing chips of the Calcium Carbonate, as it was a time consuming and tedious job finding chips that weighed exactly 0.2 g.
To improve an aspect of the investigation I think I could have used one single piece of Calcium Carbonate weighing exactly 0.2 g, instead of two or three pieces weighing a collective 0.2 g. This most probably had affected the investigation when collecting the readings and tabulating the results, as they wouldn't have been as accurate as possible. Being many pieces it would increase the surface area of the chips, compared to one single chip, which is a factor that can affect the rate of a reaction thus causing the results to incorrect.
If I had carried out a second investigation it would have reinforced what I have already concluded. A second investigation should produce similar results to those that I have collected, and so a second conclusion would relate and back up what I had previously found out.
