An investigation into how surface area affects the rate of reaction.
An investigation into how surface area affects the rate of reaction
Aim: To investigate the factors which affect the rate of reaction between marble chips and hydrochloric acid, with one in specific detail.
Scientific knowledge:
Marble chips erode when they are exposed to acid rain or pollution. Erosion is evident when you look at older marble buildings as in certain cases the erosion take a long time. It is more likely to occur in areas, where there is more pollution. This is because there are a greater number of industries in city than in the countryside. Especially the higher amount of cars which release carbon dioxide, formed as a waste gas in reactions such as internal combustion. Carbonic acid (the product of carbon dioxide and water) mixes with acidic pollutants such as sulphur dioxide and oxides of nitrogen to form acid rain. When this rain contacts the rocks, a chemical reaction takes place, weathering the rock. Sulphur dioxide and oxides of nitrogen produced by industries in the cities also increase acid rain; hence, acid rain is more common in cities than anywhere else.
Marble is a metamorphic rock, which means that the rock consists of inter locking crystals and the rock itself is very hard. To have gained this state, the rock was compressed and heated over thousands of years by tectonic activity.
Metal Carbonate + Acid Salt + Water + Carbon dioxide
Calcium Carbonate + Hydrochloric acid = Calcium Chloride + Water +Carbon dioxide
2 HCL (aq) + CaCO3 = CaCl2 (s) + H2O (l) + CO2 (g)
To speed up the rate of a reaction, you can:
* Add a catalyst
* Increase the temperature
* Increase the surface area
* Increase the concentration
These four methods all link in with the "Collision Theory"
The basics of Collision Theory:
Collision Theory relates to the number of molecules in the reaction, the chance of colliding correctly and the correct amount of energy.
For a reaction to take place between two substances, their particles must collide, so if more collisions occur, the rate of the reaction increases. However only some collisions are successful. This is because not all particles have enough energy to break bonds in other particles. We can alter the conditions under which the reaction takes place so that more collisions occur in a given period of time and so that the rate will increase.
Catalysts:
The introduction of a catalyst means that less energy needs to be used for a successful collision. If each collision requires less energy, then more collisions can take place in a shorter period of time. They also provide a surface for the molecule to attach to, increasing the probability of particles bumping into each other. However, each different reaction needs a unique catalyst.
Surface of a catalyst
Temperatures:
Increasing the temperature gives the particles more energy, resulting in faster moving particles and, consequently, more collisions and an increased rate of reaction.
When the reactants are heated, the rate generally increases. When the reactants are cooled, the reaction generally goes slower. According to the collision theory, particles must collide in order to react. Heat gives the particles more energy to move around and so they increase their speed. This increases the chances of a collision, and more importantly a successful one, as they are hitting each other with greater force with increased energy. On the other hand, cooling has the opposite effects and the chances of successful collisions are reduced.
Cold Hot
Surface Area:
A smaller piece within a large surface area means more areas of contact, resulting in an increased number of collisions and, so, an increased reaction rate.
When the surface area of the solid reactant is increased, i.e. the reactant is powdered, the rate of the reaction will also increase. This is because there are more particles exposed for the particles of the other reactant, e.g. acid to collide with. The more particles exposed, the more collisions and so a faster rate. If there are less particles exposed, e.g. the reactant is in lumps, there will be less collisions and the rate will decrease.
Concentration of acid
If an acid is used in a reaction, its concentration can affect the rate. At ...
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When the surface area of the solid reactant is increased, i.e. the reactant is powdered, the rate of the reaction will also increase. This is because there are more particles exposed for the particles of the other reactant, e.g. acid to collide with. The more particles exposed, the more collisions and so a faster rate. If there are less particles exposed, e.g. the reactant is in lumps, there will be less collisions and the rate will decrease.
Concentration of acid
If an acid is used in a reaction, its concentration can affect the rate. At a high concentration, there are more acid particles in a certain volume. This means there is a higher chance of a collision because there are more acid particles. As there are more collisions, the rate of the reaction will increase. At a low concentration, there are less acid particles in a certain volume. Therefore there is a lower chance of a collision because there are less acid particles. Because there are fewer collisions, the rate will decrease.
An increased concentration means more particles. This increases the chance of a collision and, hence, an increased rate of reaction.
Low pressure or concentration High pressure or concentration
Prediction: (activation energy and collision theory)
In Brief:
Using the scientific knowledge, stated above, I predict the rate of reaction increases when the surface area of a solid reactant is increased. This happens because by increasing the surface area we are also increasing the rate of collisions between the particles. When there is more of the reactant to react with the reaction speeds up. Therefore, my hypothesis is: the reaction will be faster when using small chips, so the gas will be produced faster (the same amount of gas will be produced in all experiments).
I predict that as the size of particles decreases, surface area will increase causing the average collision of particles to increase. An increase in rate of collision causes an equal increase in the rate of reaction. This is based on the collision theory that states that for a reaction to occur between two particles, an effective collision must take place to form product molecules. The reaction rate is the measure of how frequently effective collisions occur.
For every chemical reaction, there is a certain minimum energy needed in the collisions before a reaction can occur, because the bonds between the atoms must be broken before new molecules can be made. This minimum energy is called the activation energy (EA) of the reaction. If the colliding molecules have enough energy, the collision is successful and a reaction occurs
As a result, of increase in surface area, I predict that there is greater area for contact between the chips and the acid for reactions to take place therefore increasing rate of reaction. The rate simply depends on how fast and often particles collide with each other.
The energy (gas) given off becomes more as surface area increases, therefore I predict the reaction using the powdered chips will produce the highest amount of gas in the time allowed
Based on my own knowledge, if I were to predict the shape of the graph for a certain size of chips at this early stage in the investigation, given the amount of gas produced and the time taken, I would expect the graph to be like this:
I could investigate any of these factors, but I am going to investigate the effect of surface area of marble chips.
I have chosen this variable because:-
The temperature will be very hard to control, as it never remains constant and difficult to get the exactly right temperture.
I do not have the use of a catalyst, as there isn't one for this particular reaction.
Equipment:
A stopwatch, a conical flask, a delivery tube, an electronic scale, rubber tube, water, basin, 3 different sizes of Marble chips (preferably - large, small and powdered.), Hydrochloric Acid.
Diagram
Method
. Set the apparatus as shown above.
2. I will measure out 25cm3 of 1 Mole of Hydrochloric Acid. I did this by using a measuring cylinder.
3. I will pour the acid into the conical flask. For safety I will wear goggles.
4. I will measure out 4g of marble chips on a scale and put them in the flask, as soon as all the marble chips are in the flask, I will put the rubber tube in the flask and start the stopwatch.
5. For every 15 seconds, I will take the measurement of the of gas produced, in the measuring cylinder by looking at the stopwatch continuously to see the time the reaction has had.
6. I will repeat steps 1-4 while changing the size of the marble chips, as I am using 3 sizes - Small, Medium, and Large, I will start sequentially with the smallest one. Making sure taking the same amount of chips and hydrochloric acid at each time.
7. If time allows, repeat the experiments in order to improve the reliability of the results.
Variables:
Independent variable: This will be the size of the chips as this is the factor that I intend to change.
In our experiment involving surface area the independent variable is the surface area. The independent variable is the part of the experiment that can be changed, i.e. in this case we are changing the surface area so it is the independent variable'.
Dependant variable: The volume of gas produced and the rate of the reaction as this will change because of this.
The dependent variable in our experiment is the CO2. The dependent variable is the part of the experiment that changes as a result of changing the independent variable.
Control Variable: Keeping this the same throughout the experiment will result in a fair test. They are the total mass of marble chips, concentration of the hydrochloric acid, and the temperature of the room and volume of HCL
The fixed variable in our experiment is the temperature and the concentration of hydrochloric acid. The concentration of HCL is always the same and in order for it to be a fair test it cannot be changed. The temperature is always room temperature.
Fair Test
My experiment will be a fair test as I have use the same equipment and I will use a measuring cylinder to ensure that I measure out the same quantity of acid each time. I will use the same mass of chips so that there are not varying amounts of marble chip particles, as more chips would mean more reacting and vice versa, yet I changed their surface area.
I will try my best to ensure that the temperature is the same throughout the experiment as the temperature can affect the rate of reaction, as stated in my scientific knowledge.
I started the stopwatch when all the chips were been poured into the conical flask and the rubber tube has been attached to the flask. This is so that if any gas escapes, it is approximately the same quantity each time.
I repeated the results 3 time so that I can spot any anomalies due to inaccuracies.
In order to keep a fair test, only the surface area (i.e. size) of the marbled chips is variable. Other variables are to be kept constant to avoid obtaining wrong results. These other variables include:
*Temperature: -temperature of the reactants are kept at room temperature.
*Volume of acid: - the volume of acid is kept constant at 25cm3
*Concentration of acid: - the concentration of acid is kept constant at 1Mol/dm3.
*Mass of chips: - the mass of chips use is fixed at 4g.
*Surface area of the conical flask: - the size of the conical flask is kept constant.
The HCl cannot be used again after the reaction because the acid becomes less strong to react with the acid.
In taking the readings of gas from the cylinder, I need to be accurate in taking my readings as an inaccurate reading may cause errors and alter my results. The surface area of the chips needs to be appropriate and vary in different experiments to get the correct rate of the reacting size.
Safety
In order to make the experiment safe goggles and lab coats must be worn at all times as a protection in case of a spillage. Tie up hair so that I can see what I am doing and so that there is minimum risk of it being burnt if someone else in the lab is using a Bunsen burner, or knocking over equipment that happens to be lying around. we have to be careful because the acid is highly corrosive to our bodies and should be kept away from skin and from our clothes.
Preliminary Experiment
Apparatus: Listed above
Preliminary Experiment:
This is designed to see how much I need of marble chips in relation to the Hydrochloric Acid.
I need to do some preliminary work before I start my main experiment. This is so I can check that my measurements of marble chips and hydrochloric acid are correct, and that the range of surface area I have chosen are suitable.
To start I will use:
4 g Marble Chips
25 ml HCL
and 1m
Powdered chips
Table of results
Size of chips
Mass (g) of marble chips
Volume of
HCL
Amount of CO2 (cm3) produced every 15 sec
Medium
(9-12mm)
4g
25 ml
0,3,7,10,13,18,21,24,27,34,36,40,42,
45,46,50,52,54,56,57,60,61,63,63,66,67,
69,70,72,74,75,79,79,79,80,81,81,82,82,
84,85,87,87,89,90,90,92,92,92,
93,92,95,97,99,100 Altogether 14min and 50 sec
Small
(2-4mm)
4g
25ml
2,15,27,37,47,57,64,70,75,80,84,88,91,
95,99,99,100
Altogether 4min and 15sec
Powdered
4g
25ml
0,18,23,54,55,57,57,64,54,65,65,65,65
Altogether 3min and 15 sec
Average results
Size of chips
Total volume of CO2 (g) (cm3)
Total time for reaction
Average Rate of reaction
Medium
(9-12mm)
00 cm3
5 sec
00-15=6.6 cm3
Small
(2-4mm)
00 cm3
5 sec
00-15=6.6 cm3
Powdered
00 cm3
5 sec
65-15=4.3 cm3
Conclusion:
From this preliminary experiment I have found that:
* 4g of small size marble chips and 25cm3 of 1 mole hydrochloric acid produced 59ml of gas on average.
* 4g of powdered marble chips and 25cm3 of 1 mole hydrochloric acid produced 66ml of gas on average.
* 4g of large size marble chips and 25cm3 of 1 mole hydrochloric acid produced 49ml of gas on average.
Seeing as the large marble chips took so long to react, I will change the amount of marble chips from 4g to 4.5g in the final experiment.
I have changed the length of the interval of the powdered marble from being 15sec to 5secs because the rate of reaction is too fast and also because this will help me to gain more results and hence a more reliable set of results, which will finally leave me with a more, sound conclusion.
Final Experiment
st experiment
Size of chips
Mass (g) of marble chips
Volume of
HCL
Amount of CO2 (cm3) produced every 15 sec
5 sec
Medium
(9-12mm)
4g
25 ml
0,25,42,59,75,87,98
2min and 15 sec
5 sec
Small
(2-4mm)
4g
25ml
20,49,75,98
min
5 sec
Powdered
4g
25ml
32,35,37,39,41,41,43,43,44,46,52
55secs
Average results
Size of chips
Total volume of CO2 (g) (cm3)
Total time for reaction
Average Rate of reaction
Medium
(9-12mm)
98 cm3
5 sec
98-15=6.3 cm3
Small
(2-4mm)
98 cm3
5 sec
98-15=6.3 cm3
Powdered
52 cm3
5 sec
52-5=10.4 cm3
2nd experiment
Size of chips
Mass (g) of marble chips
Volume of
HCL
Amount of CO2 (cm3) produced every 15 sec
5 sec
Medium
(9-12mm)
4g
25 ml
0,5,9,20,28,35,45,52,58,64,73,78,84,88,92,
94,98,100
4min and 50 sec
5 sec
Small
(2-4mm)
4g
25ml
5,32,65,85,100
min and 15 sec
5 sec
Powdered
4g
25ml
90,93,95,96,96,97,97,97,98,98,98
55 sec
Average Results
Size of chips
Total volume of CO2 (g) (cm3)
Total time for reaction
Average Rate of reaction
Medium
(9-12mm)
00 cm3
5 sec
00-15=6.6 cm3
Small
(2-4mm)
00 cm3
5 sec
00-15=6.6 cm3
Powdered
98 cm3
55 sec
98-5=19.6 cm3
3rd Experiment
Size of chips
Mass (g) of marble chips
Volume of
HCL
Amount of CO2 (cm3) produced every 15 sec
5 sec
Medium
(9-12mm)
4g
25 ml
9,20,33,46,55,65,75,85,92,107
2min and 50sec
5 sec
Small
(2-4mm)
4g
25ml
20,42,64,81,101
min and 15 sec
5 sec
Powdered
4g
25ml
95,102,105,107,109
25sec
Average Results
Size of chips
Total volume of CO2 (g) (cm3)
Total time for reaction
Average Rate of reaction
Medium
(9-12mm)
07 cm3
5 sec
07-15=7.13 cm3
Small
(2-4mm)
01 cm3
5 sec
01-15=6.73 cm3
Powdered
09 cm3
5 sec
09-5=21.8 cm3
4th Experiment
Size of chips
Mass (g) of marble chips
Volume of
HCL
Amount of CO2 (cm3) produced every 15 sec
5 sec
Medium
(9-12mm)
4g
25 ml
5,18,33,45,59,69,80,92
2min
5 sec
Small
(2-4mm)
4g
25ml
20,42,64,81,101
min and 15 sec
5 sec
Powdered
4g
25ml
42,44,45,46,47,47,47,48,49,49,
49,49
min
Average results
Size of chips
Total volume of CO2 (g) (cm3)
Total time for reaction
Average Rate of reaction
Medium
(9-12mm)
92 cm3
5 sec
92-15=6.13 cm3
Small
(2-4mm)
01 cm3
5 sec
01-15=6.73 cm3
Powdered
49 cm3
5 sec
49-5=9.8 cm3
Analysing Evidence and Drawing a Conclusion
The results should have concluded my theory that as the size of the CaCO3 decreased the rate of the reaction should have increased. I can prove this because the smaller the pieces of CaCO3 the more area there is for the HCl to collide with and the reaction should get faster. This is shown in the diagrams below:
These diagrams are showing that because the CaCO3 particles are more dispersed in the right diagram than the left and so there is more chance of a HCl particle hitting a CaCO3 particle.
Anomalous results - The circled results in my graph, appear to be anomalies, I can see that they are anomalous because they do not fit the predicted graph or the line of best fit.
Furthermore, if we calculate the average amount of gas produced every 15 seconds for each reaction, it is quite evident that not only is more gas produced with a larger surface area, but also that it is produced much faster. In the large pieces, there was an average of 6.54 cm3 of gas produced every 15 seconds. In the medium-sized pieces, there was an average of 6.59 cm3 of gas produced every 15 seconds. Lastly, in the powder, there was an average of 15.4 cm3 of gas produced every 5 seconds.
My prediction was correct because the surface area of the smaller pieces was bigger than that of the larger pieces. This is because when a solid is broken down into many smaller pieces it has a larger surface area and therefore it can react with more of the hydrochloric acid. In this experiment as the surface area was increased the reaction took place a lot quicker proving my earlier theory correct. Therefore as the surface area increased so did the rate at which the CO2 was produced.
From my graphs it can be spotted that there is not much of a difference between the medium marble chips and the small marble chips. The main difference was between the powdered marble chips and the medium marble chips. Graph 2 and 3 shows this clearly. This again shows that my prediction was correct.
