3) Size of solid Particles (or SURFACE AREA) increases collisions
If one of the reactants is a solid then breaking it up into smaller pieces will increase its surface area. This means the particles around it in the solution will have more area to work on so there’ll be more useful collisions.
Surface area: large particles have a small surface area in relation to their volume so there are fewer particles that are exposed and available for collisions. This results in fewer collisions and therefore means the reaction is slower. When we use a smaller solid reactant (by breaking them down into pieces) you are increasing the surface area and that makes the reaction occur faster because there is more surface to collide on. If one of the reactants is a solid, the surface area of the solid will affect how fast the reaction goes. This is because the two types of molecule can only bump into each other at the surface of the solid. So the larger the surface area of the solid, the faster the reaction will be.
4) Catalyst increases the number of collisions
A catalyst works by giving the reacting particles a surface to stick to where they can bump into each other.
Catalysts: a catalyst is a substance which increases the rate of a chemical reaction, without being used up in the process. It can be used more than once to increase the rate of conversion of reactants into products. A catalyst lowers the amount of energy needed for a successful collision (activation energy) - so more collisions will be successful and the reaction will be faster.
It basically provides a surface for the molecules to attach to, thereby increasing their chances of bumping into each other.
So above are the four ways of increasing the rate of reaction. There are also two other simple ways of increasing the rate of reaction. These are:
- Stirring – The effect of stirring increases the rate of reaction because it causes the particles to move quicker and so each collision between the particles becomes more violent. As the particles move around faster they gain more energy also which in turn helps to make the collision much more vigorous. How much the stirring affects the rate of reaction depends upon the speed of which you stir at. The faster you stir the quicker the rate of reaction because the particles will gain more energy at a faster speed.
- Pressure – Increasing the pressure is similar to increasing the concentration. The particles will collide more frequently at a higher pressure and increase the rate of reaction. The pressure though only has a big effect on gases and not liquids, which is why it will not be a major factor to control.
Aim
The aim of the investigation is to find out what affects the rate of reaction between calcium carbonate and hydrochloric acid.
Variables
There are many variables that affect the rate of reaction. These variables are:
- Concentration of reactants
- Temperature
- Use of Catalyst
- Surface area
Concentration is the most important variable in this investigation. This is because increasing the concentration would therefore increase the rate of reaction. In this case there would be different molarity of Hydrochloric acid used. Basically the higher the molarity the more the concentration and so the faster the rate of reaction. Molarity is similar to concentration. If I use 1 mole of Hydrochloric acid a certain amount of carbon dioxide will form at a specific time. But for instance I use Hydrochloric acid of a higher concentration for example: 3 moles. The same amount of Carbon Dioxide will form overall but the rate of reaction will increase and therefore the Carbon Dioxide will form faster.
The temperature of the room the experiment will be held in also affects the rate of reaction. Also depends on the weather and whether the central heating is turned on or off. Usually room temperature is approximately 23 degrees Celsius but due to other factors such as central heating it can be increased. So if the room is made hotter then the rate of reaction will be faster than when the experiment is done under room temperature. So in a heated room the particles will travel faster because they will receive energy and so will collide more often at a higher speed as the particles now have more collisions. This increases the rate of reaction. Also if the room temperature is decreased then the rate of reaction will decrease because the particles will have less energy, so less kinetic energy and so means the rate of reaction will be slower. This means that the acid particles will have less energy and so will the Calcium and so both reactants will be affected because of temperature.
Using a catalyst will also increase the rate of reaction. This is because the catalyst produces an area for both reactants to stick on increasing the probability of collisions and so therefore there are more collisions increasing the rate of reaction. Also as mentioned before – the least amount of energy needed for the reactants to actually react is known as the activation energy. Catalysts decrease the activation energy so the reactants will react at a lower energy level and so also increases the rate of reaction. So less energy will be needed for the hydrochloric acid and the calcium carbonate to react. If a catalyst is not used then the rate of reaction stays the same – and so when a catalyst is used the rate of reaction is increased without reacting itself or being used up.
The surface area is another variable that affects the rate of reaction. In this case the Calcium Carbonate is the reactant that is affected by surface area. If the calcium carbonate has a small surface area then there would be less area exposed for collision attempts. So at any one time less calcium carbonate will be collided with decreasing the rate of reaction. On the other hand if the large solid is broken down the surface area would increase leaving more area exposed. So now there are more area exposed and so there will be more collisions because the Hydrochloric acid molecules have more calcium carbonate molecules to collide with.
PREDICTION:
I shall be measuring how the change in the rates of reaction changes when the concentration of acid is changed. This change in concentration will affect the rate of reaction because when acid is diluted there is more space for the particles to move so fewer collisions take place – also the more concentrated the solution the less space there is between particles and so the more frequent number of collisions.
I predict that the rate of reaction will be lowest when the lowest concentration of hydrochloric acid is used. This means the rate of reaction will be lowest when the molarity of the hydrochloric acid is 0.5. So I also predict that the rate of reaction will be highest when the concentration of the hydrochloric acid is highest and so for this investigation I predict that the rate of reaction will be highest when the molarity of the hydrochloric acid is 4. This is because 0.5 moles compared to 4 moles is eight times less. This means there are eight times less particles for the 0.5 moles than the 4 moles. So it will also be eight times more packed. This doesn’t mean that there will be eight times more collisions but the probability of there being a successful collision increases by eight times.
Although there are eight times more particles in hydrochloric acid that is of molarity 4 compared to the hydrochloric acid that is of molarity 0.5 it doesn’t mean that the rate of reaction will be eight times faster. It just means there are eight times more particles in the relative same amount of volume. This mans the hydrochloric acid have less space between particles and so there are more frequent collisions. The reason why the rate of reaction does not increase by eight times is because the particles move at a constant rapid random motion. This means they move continuously and randomly so moves at different directions and so the rate of reaction does not increase at a fixed rate in comparison to its molarity but the number of successful collisions just increase.
Just as four moles of hydrochloric acid will have will have eight times more particles than 0.5 moles of hydrochloric acid 2 moles of hydrochloric acid will have twice as much as particles as 1 mole of hydrochloric acid and so 3 moles of hydrochloric acid will have three times as much particle as 1 mole of hydrochloric acid.
Low concentration of particles (for example 0.5 moles of hydrochloric acid).
High concentration of particles (for example 4 moles of hydrochloric acid).
How I predict my graphs to be:
The graph for molarity 4 will be approximately as below compared to the graph on the right. The trend will be less steep for 0.5 moles.
PLAN
I plan to find out what affects the rate of reaction between calcium carbonate and hydrochloric acid. The variable I am going to change is concentration. These are the concentrations I am going to use:
0.5 mole dm3
1 mole dm3
2 mole dm3
3 mole dm3
4 mole dm3
In this experiment I am measuring the amount of gas given off. Because of this I am going to use he gas syringe to measure how much gas is produced. Once each test is started the amount of gas produced every 20 seconds will be recorded. Below is a diagram that shows how the gas is produced and measured using a gas syringe:
Three tests will be carried out for each molarity. This is to see whether the experiment is well carried out or not. Anomalous results may rise. If on of the tests are wrong then there will be results which highly differentiate – and this suggests that the tests are wrong. Three tests carried out mean for each use of molarity the tests will be repeated 2 more times so I will have three different sets of results for each molarity for e.g. 3 tests for 0.5moles; 3 test for 1 mole etc… Throughout the whole experiment the volume of hydrochloric acid will remain the same – 10cm³. Also the same mass of calcium carbonate will be used and its surface area will remain the same. Although it would be good to include a catalyst to increase the rate of reaction, it will not be used.
Preliminary tests were conducted before the experiment. In this case the preliminary test was to decide whether a digital or analogue scale should be used. What I found out was that there the digital one was better to use as it shows the mass as decimals. The problem with the analogue scale was that it cannot show the mass through decimals but only integers (whole numbers). Mass is harder to read off from an analogue scale than it is from a digital one. So the digital scale is easier to use in a continuous experiment and so is more precise to use.
Equipment:
- 3 Large boiling tubes
- Test Tube rack
- Digital Stop Clock
- Hydrochloric Acid (of different molarities, 0.5m; 1m; 2m; 3m and 4m)
- Calcium Carbonate (Medium surface area pieces)
- Gas Syringe (Maximum capacity of 100ml)
- Digital Scales
METHOD:
- Firstly, get 3 large boiling tubes and place them in a test tube rack.
- Measure 1 gram of calcium carbonate using the digital scales (in small pieces), and place it in a boiling tube. Do the same for the other boiling tubes.
- Using a measuring cylinder measure 10cm³ of hydrochloric acid then pour into the boiling tube.
- Attach gas syringe to boiling tube instantly.
- Record reading of gas syringe (amount of CO2 produced) every 20 seconds.
- Input measurement into a table.
- Repeat experiment two more times using the same concentration (molarity) or HCl.
- Repeat the experiment using different molarities and repeat each concentration twice.
- When measuring use the stop clock to know exactly every 20 seconds and that amount of CO2 produced is recorded every 20 seconds accurately.
- Calculate average times for reactions and record in table.
- Calculate rate of reaction for all the molarity experiments (rate of reaction for 0.5 moles and then 1 mole etc…)
Fair Test:
To keep the test fair the beakers would be cleaned with water after each test so there is no excess reactants in the next test. After each test the gas formed would be pushed out from the gas syringe. The mass of the calcium carbonate will be measured to exactly 1 gram – not 0.1g less or more.
Results Tables:
Results Table 1:
Molarity of HCl: 0.5 mole dm3
Volume of HCl: 10CM³
Mass of Calcium Carbonate: 1 Gram
Results Table 2:
Molarity of HCl: 1 mole dm3
Volume of HCl: 10CM³
Mass of Calcium Carbonate: 1 Gram
Results Table 3:
Molarity of HC: 2 mole dm3
Volume of HCl: 10CM³
Mass of Calcium Carbonate: 1 Gram
Results Table 4:
Molarity of HCl: 3 mole dm3
Volume of HCl: 10CM³
Mass of Calcium Carbonate: 1 Gram
Results Table 5:
Molarity of HCl: 4 mole dm3
Volume of HCl: 10CM³
Mass of Calcium Carbonate: 1 Gram
As the graphs show the higher the concentration, the faster the rate of reaction. The graph which includes all the four concentration shows this. As the concentration increases the gradient increases. All three of my graphs show a positive correlation where either as time increases the production of C02 increases or as concentration increases the production of C02 increases. Graph 1 shows the curves for every molarity. As you can see all the curves have a different gradient. The curve with the lowest gradient is of the curve with the lowest molarity. The higher the molarity, the bigger the gradient of the curve. Graph 3 shows the average volume of C02 produced in all the concentrations. The curve is positive. This means that the higher the concentration the faster the production of C02. Graph 3 shows a graph on the rate of reaction of all the different concentrations used. As you can see as the concentration of HCl increases the rate of reaction increases. So my graphs have proved most of my predictions and have shown strong positive correlations. All the lines of best fit show positive correlations.
Conclusion
My prediction was proven correct according to my results tables. As I predicted the higher the concentration (molarity) the higher the rate of reaction. My results prove my prediction well. As I predicted increasing concentration means increasing the number of particles while having the same amount of volume. These results in the solution consisting of particles that is more crowded. This increases the probability of the particles reacting as there is less space than before and so they collide more often. The more the particles the more the chance of collisions take place and so HCl of molarity 4 has the most particles and so the rate of reaction is fastest. Also I included in my prediction that if the molarity increases by a certain scale factor it doesn’t mean that the rate of reaction will also increase by that factor. As stated before the molarity of HCl of 0.5 and 4 for example. Both solutions are HCl and of the same volume – but the difference is that the one with molarity 4 consists of 8 times more particles than the solution with molarity 0.5. This just increases the number of particles but and also increases the probability of successful collisions. This doesn’t mean the rate of reaction will be 8 times faster. This is proven by my results. The rate of reaction for HCl of molarity 0.5 is 0.03 CM³/S. The rate of reaction for HCl of molarity 4 is 1.46 CM³/S which is 48.6 times faster than the HCl of molarity 0.5. This proves my prediction because I mentioned that they would not be 8 times faster if there are 8 times more particles – in this case 48.6 times faster. Also for 1 mole of HCl the rate of reaction was 0.36 CM³/S. The rate of reaction for HCl of 2 moles is 0.92 CM³/S. Although there is twice the number of particles at the same volume the reaction is 2.5 times faster. The rate of reaction is not directly proportional to the concentration – if concentration increases by a certain factor rate of reaction doesn’t increase at that factor. This is mainly due to the fact that the particles move at a constant rapid random motion – so they all move rapidly but randomly which is why rate of reaction is not directly proportional to the concentration. So the HCl of molarity 4 had the greatest number of particles compared to the other molarities and therefore had a reduced probability of steric hindrance – which is another cause for the increase in the rate of reaction.
Also my graphs show the gradient is increasing which proves my main hypothesis of rate of reaction increasing as concentration of the solution.
Evaluation
This experiment has vastly improved my research skills with using books from the library and using the Internet more efficiently. School experiments are not 100% fair due to the lack of advanced technology - the experiment is right to a degree of accuracy and is enough to obtain (draw out) the main ideas. My experiment went very well and again was very successful. The method was followed exactly as suggested and so all the results conducted were accurate. To keep the experiment fair each test was repeated 3 times. If an experiment is carried out there may be mistakes which the user cannot recover and may record the information drawing out false conclusions leading to a wrong investigation. For this particular reason tests were repeated to draw out anomalous results. These results would be much different compared to the others. For example: Test 1: 5cm; Test 2: 6cm and Test 3:14cm. Immediately it will draw attention showing the anomalous result which is completely different to the other two results. Although there were no anomalous results there was a problem that was spot in one of the results table. There was one results table that drew my attention – Table 5. For the 3rd test the difference between the 120 second reading and the 100 second reading was higher than both the 1st and 2nd reading. Although my results were accurate and did prove my prediction correct there are still many various ways that the investigation could have improved/extended. Again we are using school equipment – they are not highly efficient and are not the state of the art equipments and so have defects. One problem was that after placing the two reactants into the test tube we had to quickly attach the gas syringe to the test tube. The reaction started instantly and so during those 1 or 2 seconds of attachment there was a slight loss of Carbon Dioxide. Although this was the case id did not affect the experiment much as we still would’ve obtain the same ideas and proofs as modern scientists would. The investigation could be extended to give a broader and vaster set of results which can draw bigger conclusions. In this experiment the concentrations or molarities used were 0.5, 1, 2, 3 and 4 moles. The investigation can be extended by using bigger concentrations of Hydrochloric acid. Along with this more tests could have been conducted instead of 3. This would make the average more reliable to use.
There is another huge improvement that can be made and may slightly change my results. This is due to room temperature. The experiments were carried out through 2 weeks. During those days there was many weather changes that has affected room temperature and can slightly alter my results compared to if I did all of it in one day. An alternative method I could’ve used is the water bath. So temperature has caused the reaction to work at different rates but the room temperature has only differed by approximately 1 degree Celsius and so does not have a huge impact on my results – in order to make it more reliable and fair it would be best to use the water method or to do it all in one day. If the temperature is slower the rate of reaction becomes slower because the particles have less kinetic energy and so move at a slower speed. If the temperature is increased then the particles would move much faster because they’ll have more kinetic energy. The water method would resolve this problem as it can keep the temperature of the HCl constant without altering the temperature – this means the particles would have the same amount of kinetic energy throughout the whole experiment.
The experiment can be extended by using a bigger gas syringe which can hold more volumes of gas. This will be needed for use of larger concentrations. Also the experiment can be lengthened by experimenting for more than 120 seconds (2 minutes) the experiment could be extended to 180 seconds (3 minutes). This all would give a broader more useful and reliable set of results.
One improvement that could’ve been made is checking the actual molarities. Although the bottle stated that the HCl was of a certain concentration it doesn’t mean that there weren’t any mistakes. If this was the cause then the HCl used may be 0.7moles other than stated 1 mole. The actual molarity of the HCl may be higher or below the molarity stated. An increase in molarity means an increase of the rate of reaction; alternatively a decrease in molarity means a decrease in the rate of reaction. This would highly affect my results because my results are basically conducting the rate of reactions using certain concentrations – this would prove my predictions wrong. I am pretty much sure the actual molarity wasn’t different from the molarity stated because my results did not contain any anomalous results and so proved my prediction correct.
Ways in which my investigation could have been improved:
- Increase molarities to 5 moles and 6 moles etc…
- Use a larger gas syringe
- Use the water bath method
- Extend experiment to 3 minutes/180 seconds
- Conduct more tests instead of 3
- Check molarity before use
My results have been very accurate. My predictions have all been proved correct which shows all the relative understandings of theories such as the collision theory. So as said before the higher the concentration the faster the rate of reaction. This is shown – the highest concentration used was 4 moles and so the rate of reaction was fastest.
Bibliography:
- The Essentials of OCR SCIENCE: DOULE AWARD B STAGED ASSESSMENT Phase 1 Modules 2001 Lonsdale
- CGP GCSE Double Chemistry
-
GCSE Bitesize Revision Website
- www.chemguide.co.uk