INTRODUCTION
Why should this coursework be entitled "The Crumbling Taj"? The Taj Mahal is a famous beautiful building found near Delhi in India. It is made of marble, which is a polymorphic form of calcium carbonate. Unfortunately it is slowly being damaged by acidic rain. This occurs in two forms:
* Natural carbonic acid formed when carbon dioxide dissolves in water.
* Acid rain made of a mixture of sulphurous acid, sulphuric acid and nitric acid. These acids are formed from pollution from the burning of fossil fuels and from the discharged exhaust from road transport.
Although hydrochloric acid is not one of these mentioned, it is convenient to use in this experiment, as it is available in our laboratory. The active ion, H3O+ in all acids is present in hydrochloric acid just as much as it is present in all the other acids mentioned.
AIM
The aim of my investigation is to design and carry out a series of experiments to discover how the speed of chemical reaction between calcium carbonate (marble) and acid can be altered. I will be looking at the following equation:
CaCO3 + 2HCl --> CaCl2 + H2O + CO2
Calcium Carbonate (marble) + Hydrochloric Acid --> CalciumChloride + Water + Carbon Dioxide
The aim for my investigation is to also find out the best conditions at which the reaction rate will be at its fastest. These conditions are factors that can normally affect reaction rate. They are the variables.
Everyday we are concerned about how fast things happen. We want to know how fast we can get to school, how fast a car is travelling or how fast we can run a hundred metres. Chemists are particularly interested in how fast chemical reactions happen. They want to know how quickly steel rusts, how quickly food cooks, and how quickly stone buildings are weathered by acid rain.
Different chemical reactions happen at different rates. Some reactions, like explosions are so fast they are almost instantaneous. For example, when a burning splint is put into a mixture of hydrogen and chlorine, there is a loud bang and hydrogen chloride is produced.
H2 (g) + Cl2 (g) --> 2HCl (g)
Other reactions, like rusting of steel and weathering of limestone on buildings, happen slowly that it may be years or even centuries before we notice their effects. Most reactants take place at speeds somewhere between those described above.
VARIABLE FACTORS
There are at least ten factors that affect reaction rate in some way:
. Temperature change: temperature is related to the velocity of particles. As temperature rises so the velocity of the particles increases and so collisions become more frequent and successful reaction becomes more likely.
2. Shape of molecule. E.g. an enzyme only operates a chemical reaction, as a catalyst, if its shape is precise and specific for a given substrate.
3. Catalyst: A substance that helps on or speeds up a chemical reaction without itself being changed by the end of the reaction.
4. Pressure in a gas reaction. If particles are forced together, then they are more likely to collide and therefore more likely to react.
5. Turbulence: if particles are stirred together they are more likely to collide and therefore react.
6. Strength of an Acid or Alkali: e.g. pH. When more H+ ions or OH- ions are present then reactions involving them are likely to be faster.
7. Surface area: Where surface area is increased e.g. by powdering lumps of a solid reactant then particles are more likely to collide and react at a faster rate.
8. Electric current: in an electrolysis reaction. If current is increased then more electrons per second will discharge positive ions and more electrons will be released by negative ions as they discharge.
9. Concentration: in a concentrated solution more particles of one reactant will be available in a given volume, to react with the other reactant
0. Light: some reactions depend on the intensity and frequency of light shining on them. Photography and photosynthesis are two reactions dependent on light.
This statement explains why reactions between gases and liquids usually happen faster than reactions involving solids. Particles in gases and liquids can mix and collide much more easily than particles in solids. In a solid only the particles on the surface can react. During a reaction, reactants are being used up and products are forming. So, the amount and the concentration of the reactants fall as the amount and the concentration of the product rise. The reaction rate tells us how fast or slow the reaction is taking place. We can measure reaction rates by measuring how much of a reactant is used up or how much of a product forms in a given time.
Reaction rate = Change in amount (or concentration) of substance
Time taken
Variable Factors that will affect my experiment
The variable factors that can affect my investigation are:
* Temperature change
* Concentration
* Catalysts
* Surface Area
INDEPENDENT VARIABLE
The independent variable or otherwise the variable I have chosen to investigate out of these four is Concentration.
DEPENDENT VARIABLE
The dependent variable means what I have decided to measure or observe. While carrying out the experiment I would need to observe something that would tell me how much marble is being corroded. One way of telling how much marble has been corroded is by reacting the marble with hydrochloric acid and measuring how much gas (carbon dioxide) is being given off. This is a scientific way of observing the amount of marble that has been corroded. So my dependent variable will be measuring the amount of gas (carbon dioxide) produced when marble is reacted with acid.
CONTROL VARIABLES
There are many factors in experiments that need to be kept constant or the same in order to make the experiment fair. These factors are known as control variables. For this experiment the control variables will be:
* The amount of acid should be kept the same for each experiment.
* The amount of marble should be kept the same for each of the experiments.
* The type of acid should be kept the same.
* The concentration of acid should be kept the same for each experiment.
* The Surface area of the marble should be kept the same for each of the experiments.
HYDROCHLORIC ACID - THE FACTS
* This is a solution of hydrogen chloride in water; it contains chloride (Cl-) and hydronium (H3O+) ions.
* The maximum concentration of the solution is 31%
* HCl is strong monobasic acid (another good reason for it to be used with marble in the reaction).
* HCl produces salts called chlorides.
* HCl is a very strong acid and is 85% ionised.
* HCl dissociates in Cl- (aq) and H+ ions combine with covalent H2O molecules to form H3O+ (aq) ions in solution.
* HCl releases carbon dioxide from carbonates and hydrogen carbonates. It can be oxidised to chlorine as seen by the following equation:
CaCO3 + 2HCl (aq) --> CaCl2 + H2O + CO2
METHODS OF MEASURING REACTION RATES
There are several ways that a reactions rate can be measured. Ten of them are mentioned below.
. Precipitation: This is when the product of the reaction is a precipitate that clouds the solution. E.g. using the black cross experiment with HCl + Na 2 S2O3 (aq).
2. Disappearance of a solid reactant by dissolving: The time taken for marble (calcium carbonate) to completely react with excess HCl acid, measured using different concentrations of acid for each datum value.
3. Change in mass (usually given off): Any reaction that produces a gas can be carried out on a mass balance, and as the gas is released the mass disappearing is easily measured. E.g. HCL + CaCO3 (marble) or magnesium, etc.
4. The volume of gas given off: This involves the use of a gas syringe or a graduated gas jar or an eudiometer to measure the volume of gas given off. E.g. HCl + CaCO3
5. Titration of samples: Samples are withdrawn and quenched or frozen. The concentrations of reactants or products are measured using standard solutions.
6. Colorimetry: If one of the reacting substances or products has a colour, the intensity of this colour will change during the reaction. A photoelectric device in a colorimeter could follow the intensity.
7. Dilatometry: In some reactions, the volume of a liquid mixture may change during a reaction. That change could be followed using an enclosed apparatus fitted with a capillary tube. It is called a dilatometer.
8. Measurements of electrical conductivity: If the total number of ions present in a solution varies during a reaction then there will be changes in the electrical conductivity of the solution. A conductance bridge is applied to the solution using AC. This avoids electrolysis of the solution.
9. Polarimetry: Optical isomers or chiral compounds containing asymmetric carbon atoms will rotate the plane of polarisation of polarised light by a specific angle clockwise or anticlockwise. Some chemical reactions such as the hydrolysis of sucrose (not optically active) produce optically active isomers. A polarimeter can follow the rate of chemical reaction by measuring angles of rotation per minute.
0. By measurements of changes in other physical properties: e.g. refractive index, magnetic effect, viscosity, pH, etc.
Techniques use to measure concentration vary with the reaction and the available apparatus. Titration can be done on reactions in solutions. Changes in colour can be indications of concentration change and can be measured in a spectrometer. Density and electrical conductivity may vary with concentration. For gases a pressure change may tend to indicate concentration change. The rate of reaction of a reaction is usually measured as a function of the concentration of a reactant or product over time.
Industrial chemists want to produce materials as cheaply as possible. In order to do so, they choose conductions which;
* Increase the reaction rate.
* Use the most economic method.
* Methods that either reduce reversible or at least increases the net yield in the shortest possible time.
One way to speed up reaction is to increase the concentration of reactants. At the same time, the products must be removed as fast as they form to prevent the reverse reaction happening. This is so in the Haber process for making ammonia.
Catalysts are also important in industrial processes. By using a suitable catalyst it is possible to carry out some processes, which would otherwise be impossible. Catalysts do not increase yield but they decrease the time taken to reach the products required. Other processes can be carried out at lower temperatures when a catalyst is used, which makes them more economical. Temperature and pressure are also selected cautiously in the manufacture of most chemicals. The importance of these factors in the industrial processes is well illustrated by the Haber process.
Rates of Reaction
How does a chemical reaction occur?
Particles in a substance are moving all the time. In liquids or gasses the particles are free to move their positions and particles are colliding all the time. A chemical reaction occurs when the particles of the reactants collide with enough energy to break the bonds between them. The amount of energy needed to make this happen is called activation energy. The activation energy differs for different reactions. If the activation energy is low there are lots of collisions with enough energy to "react" and the reaction ...
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Rates of Reaction
How does a chemical reaction occur?
Particles in a substance are moving all the time. In liquids or gasses the particles are free to move their positions and particles are colliding all the time. A chemical reaction occurs when the particles of the reactants collide with enough energy to break the bonds between them. The amount of energy needed to make this happen is called activation energy. The activation energy differs for different reactions. If the activation energy is low there are lots of collisions with enough energy to "react" and the reaction takes place quickly. If the activation is high there are fewer successful collisions and the reaction is slower.
SCIENTIFIC KNOWLEDGE
THEORIES ABOUT RATES OF REACTION
KINETIC THEORY FOR RATES OF REACTION
The kinetic theory of matter is based on the idea that all matter is made up of particles, which are indivisible. The particles in all substances are continually moving. Small particles move faster than heavier particles. As the temperature rises, the particles get hotter and have more energy to move around faster. In a solid, the particles are very close with strong forces between them. Solid have a fixed shape and a fixed volume. In a liquid, the particles are a little further apart and the forces between the other. So liquids can change their shape, but they keep fixed volume. In a gas, the particles are much further apart. There are no forces to hold the particles together. The particles rush around in all directions in all the space they can find. So, gases change their shape and their volume depending no their container.
TRANSTION STATE THEORY FOR RATES OF REACTION
The theory suggests that as molecules collide and takes place, they are momentarily in a less stable state than either the reactants or the products, i.e. the atoms rearranging themselves. As the atom are separated, the potential energy of the system increases and this results in an energy barrier between the reactants and the products. An activated complex or transition state is formed. The products are formed only if the colliding molecules have sufficient energy to overcome the energy barrier; the energy required being the activation energy. The higher the activation energy the lower the number of effective collision. A diagram of the energy barrier between the reactants and products is given on the next page:
ACTIVATION THEORY
Activation energy is the minimum energy that the particles of reactants must have for them to react when they collide. The rate of reaction that depends on how many reacting particles have the minimum energy is called the exothermic reaction. In many reactions the particles already have this energy and react straight away. This is called the endothermic reaction. In others, energy has to be supplied for the particles to reach the activation energy.
COLLISION THEORY FOR RATES OF REACTION
Reaction rates are explained perfectly by the Collision Theory. It's really simple. It just says that the rate of reaction simply depends on how often and how hard the reacting particles collide with each other. Collision theory is the extension of kinetic Theory. Molecules move randomly in a gas. They collide and then bounce into other directions. Sometimes there is enough impact to allow bonds to be broken. The basic idea is that particles have to collide in order to react. For the reaction to take place a fixed amount of energy must be reached and they also have to collide hard enough as well. The amount of energy to be reached is called the activation energy (Ea). If a collision can produce the right amount of energy (if the collisions are fast enough and are in the right direction) then only a reaction will take place. A reaction can be speeded up if the numbers of the suitable collisions are increased.
FOUR FACTORS THAT AFFECT THE COLLISION THEORY
. Temperature - increases the number of collisions
When the temperature is increased the particles all move quicker. If they are
moving quicker, they are going to have more collisions.
2. Concentration (or pressure) - increases the number of collisions
If the solution is made more concentrated it means there are more particles of reactant knocking about between the water molecules, which make collisions between the important particles more likely. In a gas, increasing the pressure means the molecules are more squashed up together so there are going to be more collisions.
3. Size of solid particles (or surface area) - increases collision
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.
4. Catalyst - increases the number of collisions
A catalyst works by giving the reacting particles a surface to where they can bump into each other. This obviously increases the number of collisions too.
THE EFFECT OF TEMPERATURE ON THE RATE OF REACTION
Temperature affects the speed of reacting particles. If there is a rise in temperature, the particles are given more energy to move about more. This means they will move about more, will travel a greater distance in a given time and will collide more with the substrates meaning the collisions will exceed the activation energy and so the rate of reaction will increase.
THE EFFECT OF CONCENTRATION ON THE RATE OF REACTION
If the reacting substances are more concentrated then there will be a grater rate of reaction. This is because increasing the concentration of the reactants would mean more collisions between the particles therefore producing greater rate of reaction. This is also why the greatest rate of reaction occurs when the two substances want to react or the reactants are mixed because at this time they are at their highest concentration. If we take a simple experiment, for example: magnesium ribbon and hydrochloric acid. When we increase the concentration of the acid from 1 mole per dm3 to 2 moles per dm3 while keeping all the other variables the same, it can be seen that more bubbles of hydrogen are formed. Basically by increasing the concentration the rate of reaction also increases.
THE EFFECT OF SURFACE AREA ON THE RATE OF REATCION
When one of the reactants is a solid, the reaction must take place on the surface of the solid. By breaking up the solid into smaller pieces, the surface area is increased giving more room for collisions to take place and a greater rate for reaction.
In the diagram the Grey substance is marble and it is being reacted with the hydrochloric acid, you can see where there is a large clump of marble the hydrochloric acid cannot get to all of the marble. On the right of the large lump of marble there is the same mass of marble but in smaller pieces. Here the hydrochloric acid can come into contact with all the marble particles much more easily. This is because by decreasing the particle size there is a larger surface area for the hydrochloric acid to act upon. So this tells us that increasing the surface area also increases the rate of reaction.
THE EFFECT OF CATALYSTS ON THE RATE OF REACTION
Catalysts are substances that help change the speed of reactions (mostly faster) and remain chemically the same at the end of a reaction and their mass also remains the same at the end of a reaction. They do not produce more of the product but only the same amount and at a faster rate. There are a few catalysts that slow down the rate of reaction and they are called negative catalysts or inhibitors. Catalysts speed up reactions by providing an alternative pathway for the reaction. The catalyst to speed up the reaction has much lower activation energy than the reactants alone. This will mean that it will be quicker for this activation energy to be reached. More collisions will now lead to a reaction and so the rate of reaction will be faster.
Catalysts work best when they have a big surface area. Catalysts are normally usually used as a powder or pellets or fine gauze. This gives them maximum surface area to enable the reacting particles to meet up and do the business.
Catalysts help reduce costs in industrial reactions, which saves a lot of money simply because the plant doesn't need to operate for as long to produce the same amount of Product. Alternatively, a catalyst will allow the reaction to work at a much lower temperature and that can save a lot of money too. Catalysts are therefore very important for commercial reasons. Catalysts are used over and over again. They may need cleaning but they don't get used up. Different reactions use different catalysts.
PREDICTION The variable I have chosen to investigate in all three experiments is concentration. I predict that as the concentration of hydrochloric acid is increased the faster the amount of carbon dioxide gas will be produced therefore the faster the rate of reaction with calcium carbonate. The low concentrated acid will produce carbon dioxide slowly displacing the water very slowly, whereas the high concentrated acid will produce carbon dioxide very quickly displacing the water much quicker than the gas produced by the low concentrated acid. Basically by increasing the concentration, the rate of reaction also increases. Collision theory says that for a reaction between two particles to occur, an effective collision must take place, which is a collision that results in the formation of product molecules. Having taken into account the Collision Theory I predict that the more concentrated the acid is, then it will be able to supply more hydrogen ions and therefore more hydronium ions causing more collisions and so the quicker and more violent the reaction will be if those collisions are successful in causing a chemical reaction. The reaction rate is a measure of how frequently effective collisions occur. Any factor that increases the rate of effective collisions will also increase the rate of reaction. Also, the smaller the marble chips are, the surface area will be increased and so I would expect the reaction rate to be increased. Concentration is one factor that increases the effective number of collisions in a reaction. The more molecules present the greater the likelihood of effective collisions, which means that it also increases the rate of reaction. This theory explains why an increase in the concentration of reactants will tend to lead to an increase in the rate of reaction - there are more particles present in the same volume, and so are more likely to collide. By using powdered particles of CaCO3 rather than large particles, I will increase the surface area of the marble chips and so I predict that the rate of reaction would increase.
The reaction rate, however, should decrease as the experiment progresses because as the reaction time increases the number of hydrochloric acid molecules present will decrease as they have been reacted to form water calcium chloride and carbon dioxide. The additional water and calcium chloride present as the experiment progresses should decrease the rate of reaction because of decrease in concentration. This should make a graph of the reaction curved as the reaction rate slows down.
Kinetic theory is based on the assumption that chemical reactions take place as a result of reacting particles colliding successfully. Successful collisions need a sufficient amount of energy. Particles that posses more kinetic energy than the activation energy are able to react more successfully. The reacting particles all have different kinetic energies due to collisions hanging their speeds. Maxwell and Boltzmann presented the distribution in kinetic energies for two temperatures (high and low) in graphs called distribution curves on which the areas under the curves past the points called energy barriers represent the number of kinetic energies. The bigger the area under the curve, the greater the number of particles with a certain energy that will promote a chemical reaction. Hotter particles have extra kinetic energy after surmounting the number of collisions in unit time. These collisions are more likely to be successful as there would be more than enough energy for them.
Although I will not be looking at the factor of TEMPERATURE, I can extend my investigation and experiment the effects of temperature on the rate of reaction.
HYPOTHESIS FOR EXPERIMENT 1 - COUNTING BUBBLES Counting bubbles is an experiment which I personally think is not very fair. There may be many mistakes in counting the number of bubbles produced for five continuous minutes and so the experiment would not be accurate. Although this experiment isn't so accurate, I think that the results will still show a trend in the pattern of results. I predict that if the concentration of the HCl is doubled then the experiment will happen twice as fast.
HYPOTHESIS FOR EXPERIMENT 2 - COLLECTING GAS OVER WATER
By putting more particles into the reaction, the chance of them colliding increases and so the rate increases. Concentration is a variable that is continuous and independent. I shall test this variable by observing the rate at which hydrogen gas collects over water against the concentration of hydrochloric acid used with CaCO3.
I predict that by doubling the concentration of the acid, the rate of reaction will also double. The higher the concentration, the higher the rate of reaction.
HYPOTHESIS FOR EXPERIMENT 3 - COLLECTING GAS IN A SYRINGE
This experiment is very similar to experiment 2 (collecting gas over water) but this experiment is the most accurate out of the three that I will be carrying out.
I predict that I will have a very similar type of results and graphs as in experiment 2. I predict that the graph will have more better and accurate trend lines in the graphs showing a curved line of best fit. The higher you raise the concentration the more the particles will collide therefore corrosion of the marble will occur.
Plan for the investigation
APPARATUS
* Distilled Water
* 0.1, 0.5, 1.0, 1.5 and 2.0 molar concentration of hydrochloric acid
* Marble chips
* Scale - Top Pan Balance
* Conical Flask
* Stop watch
* Measuring cylinder (100 cm3)
* Tray
* Test Tubes
* Test Tube Rack
* Pipettes
* Delivery Tube
* Syringe
* Stand and Clamp
SAFETY RULES
I will ensure that the goggles are worn throughout the experiments. Care will be taken not to spill any of the acid. Glass will be handled with care to prevent breakages and cuts. If any sort of accident occurs amends will be made with the help of trained technicians. Large volumes of acid will not be carried around to reduce the risk of a spillage. Containers will be kept well away from edges of the benches. Low molar concentration of hydrochloric acid will be used for safety.
FAIR TEST
To perform a fair test I will do as follows:
In the experiment I will measure each substance accurately. I will carry out the experiment at the same room temperature of 20oc each time. I will wash the conical flask with distilled water after each experiment to make sure that there isn't any solution left over from the previous experiment. I will have to stay alert when counting bubbles and will have to concentrate hard. I will also repeat the test again and take the average of the two results to get an average set of results which will be more reliable. By following my fair testing the results will hopefully come out accurate. I will be alert and take the timings accurately for each of the experiments.
METHOD FOR EXPERIMENT 1 - COUNTING BUBBLES
This is how I will be carrying out my 1st experiment to find out the rate of reaction between marble and hydrochloric acid:
When doing my experiments I will use the same procedure throughout.
I will first get the necessary equipment that will be needed and will set it up as show below. I will then get 30ml of 0.1M hydrochloric acid and will put it into the conical flask. To make sure the volumes of acid and water were right we will measure the volumes of each in a measuring cylinder to be accurate. To make sure the mass of marble chips are right we would measure them on the electronic balance to one decimal place. I will then get 2grams of marble chips (roughly the same size) and I will gently put the marble chips into the solution of hydrochloric acid and will spontaneously close the conical flask with the delivery tube that is attached to a bung at the end. As soon as I close the top of the flask, I will start the stopwatch and I will start counting the bubbles, which will be coming out from the test tube. I will record the number of bubbles produced each minute up to five minutes. The bubbles that will be produced will indicate how much CO2 is being given off by the reaction between CaCO3 and 2HCl. I will carry out this experiment again for Distilled water, 0.5, 1.0, 1.5 and 2 molar to see how the concentration affect the rate of reaction. I will keep the amount of marble chips and hydrochloric acid the same for every test I carry out so it would be fair. At the end I will also carry out this experiment on distilled water so I can compare the two substances. In this experiment I will have to concentrate all the time as I will have to count the bubble for five minutes and will have to make sure that I don't miss out on counting a single bubble. After the experiment is over, I will carry out the experiment again to confirm my results and to make sure that I was counting the bubbles correctly.
This picture shows how I am going to set-up my experiment and I am going to count the bubbles that come out of the test tube.
METHOD FOR EXPERIMENT 2 - COLLECTING & MEASURING GAS
This is how I will be carrying out my 2nd experiment to find out the rate of reaction between marble and hydrochloric acid:
When doing my experiments I will use the same procedure throughout.
I will first fill the tub with tap water about half way up and fill the measuring cylinder with water and then turn the measuring cylinder upside down into the tub of water so the cylinder would still be filled with water. By doing this, we will create a slight margin of error because some of the water will be displaced when doing this although it will be very little. Then we will clamp the measuring cylinder in place. We will change the size of the cylinders; however, this will not make the test unfair. We then will put the delivery tube under the cylinder so the air from the experiment could displace the water. To make sure the volumes of acid and water were right we will measure the volumes of each in a measuring cylinder to be accurate. I will then get 30ml of 0.1M Hydrochloric acid and put it into the conical flask. To make sure the mass of marble chips are right we would measure them on the electronic balance to one decimal place. As soon as we put the Marble chips and the acid in the conical flask and close it with the bung which will be attached to a delivery tube; we will immediately start the stopwatch. We will see how long it takes (In seconds) for the measuring cylinder to fill up with 100cm3 of Carbon Dioxide gas. We will carry this experiment out on a range of different concentrations of Hydrochloric acid. I will be carrying out this experiment on 0.5M, 1.0M, 1.5M and 2.0M to see how the concentrations affect the rate of reaction. I will also use distilled water to compare it against the hydrochloric acid. After the experiment is over I shall carry out a retest to confirm my results and I will take the average out of the two results. Below it show exactly how the experiment was set up.
METHOD FOR EXPERIMENT 3 - SYRINGE TEST
This is how I will be carrying out my 3rd experiment to find out the rate of reaction between marble and hydrochloric acid:
When doing my experiments I will use the same procedure throughout.
I will first get the necessary equipment that will be needed and will set it up as show below.
In this experiment I will again experiment the time it will take for the syringe to fill up with 100cm3 of Carbon Dioxide gas. Although this experiment will be very similar to Experiment 2, this will be more accurate as the equipment used will be more appropriate. I would assume the results in this test to be very similar to Experiment 2 so I will change the amount of Marble chips and the volume of the Hydrochloric acid to experiment what different it makes. I will used 5 grams of marble chips and 50 cm3 of Hydrochloric acid in this test but will used the same range of concentrations which are, 0.1M, 0.5M, 1.0M, 1.5M, 2M and will also use distilled water. I will do the same, starting of with 0.1M Hydrochloric acid and put it into the conical flask. As soon as we put the Marble chips and the acid in the conical flask and close it with the bung which will be attached to a delivery tube; we will immediately start the stopwatch. We will see how long it takes (In seconds) for the measuring cylinder to fill up with 100cm3 of Carbon Dioxide gas. After the experiment is over I shall carry out a retest to confirm my results and I will take the average out of the two results.
Table of Results for the method of counting the bubbles.
Mass of marble
/g
Concentration of HCl in 30cm3 / M
Time
In
Mins
Bubbles collected
Expt. 1
Bubbles collected
Expt. 2
Bubbles collected
Average
Initial temperature
/ oC
2g
Distilled water
2
3
4
5
No Bubbles
No Bubbles
No Bubbles
No Bubbles
No Bubbles
No Bubbles
No Bubbles
No Bubbles
No Bubbles
No Bubbles
No Bubbles
No Bubbles
No Bubbles
No Bubbles
No Bubbles
20oC
2g
0.1 M
2
3
4
5
No Bubbles
No Bubbles
No Bubbles
No Bubbles
No Bubbles
No Bubbles
No Bubbles
No Bubbles
No Bubbles
No Bubbles
No Bubbles
No Bubbles
No Bubbles
No Bubbles
No Bubbles
20oC
2g
0.5 M
2
3
4
5
9
51
83
22
60
6
35
59
97
42
7.5
43
71
09.5
51
20oC
2g
.0 M
2
3
4
5
79
203
333
457
570
58
63
289
403
528
68.5
83
311
430
549
20oC
2g
.5 M
2
3
4
5
28
289
423
681
686
04
256
396
533
557
16
272.5
409.5
607
621.5
20oC
2g
2.0 M
2
3
4
5
56
327
478
634
786
58
338
466
589
708
57
332.5
472
611.5
747
20oC
Graph showing the results for the method of counting the bubbles.
This graph shows the results for my experiment of "Counting Bubbles" using 30ml of Hydrochloric acid and 2 grams of Marble chip. The experiment was carried out at different concentrations of the acid. The graph shows how many bubbles I counted every minute until 5 minutes. The more bubbles counted, indicated that the reaction was faster. The graph shows a clear pattern in these sets of results, climbing up steadily.
Table showing the results for the method of collecting gas.
Concentration of Hydrochloric acid (M)
Volume of HCl
/ cm3
Mass of Marble chips (g)
Room temperature
(oC)
Time taken for 100 cm3 of CO2 gas to be collected / Seconds.
Average Time / Seconds
Distilled water
30
2g
20
No reaction
-
Repeat
30
2g
20
No reaction
-
0.1 M
30
2g
20
911
907.5
Repeat
30
2g
20
904
-
0.5 M
30
2g
20
638
636
Repeat
30
2g
20
634
-
.0 M
30
2g
20
332
348.5
Repeat
30
2g
20
365
-
.5 M
30
2g
20
202
203
Repeat
30
2g
20
204
-
2.0 M
30
2g
20
24
36
Repeat
30
2g
20
48
-
Graph 1 - First attempt
Graph 2 - Retest
Graph 3 - Average
The first two graphs and the average, all indicate the same trend. That is to say as the Molarity decreases so the reaction takes longer to produce a 100cm3 of Carbon Dioxide gas over water.
The first two graphs and the average, all indicate the same trend. That is to say as the Molarity decreases so the reaction takes longer to produce a 100cm3 of Carbon Dioxide gas over water.
Below I have similar set of results but this time it is for collecting 100cm3 of Carbon Dioxide in a syringe rather than over the water.
Table showing the results for the method of collecting 100cm3 of gas in a syringe.
Concentration of Hydrochloric acid (M)
Volume of HCl
/ cm3
Mass of Marble chips (g)
Room temperature
(oC)
Time taken for 100 cm3 of CO2 gas to be collected / Seconds.
Average Time / Seconds
Distilled water
50
5g
20
No reaction
-
Repeat
50
5g
20
No reaction
-
0.1 M
50
5g
20
879
885.5
Repeat
50
5g
20
892
-
0.5 M
50
5g
20
339
347.5
Repeat
50
5g
20
356
-
.0 M
50
5g
20
44
50.5
Repeat
50
5g
20
57
-
.5 M
50
5g
20
62
65.5
Repeat
50
5g
20
69
-
2.0 M
50
5g
20
40
43
Repeat
50
5g
20
46
-
Graph 1 - First attempt
Graph 2 - Retest
Graph 3 - Average
ANALYSING MY RESULTS
Experiment 1: Counting Bubbles
These results clearly show that reaction rate increases if the molarity of the acid has been increased. The bubbles, which I was counting was an indication of how much Carbon Dioxide gas was released in the experiment. The time taken for counting the bubbles does not affect the results. Whether the molarity is 2M or 1 M, the results show the same trend for 1 minute or 2 minutes and so on up to five minutes. The coloured bar chart illustrates what I am saying. This is shown on page 19. Although this experiment was not so accurate, I still managed to get a good set of results and my graph showed a very clear pattern. The collision theory having many particles or few particles of acid available to collide with the marble holds. In other words, the greater the number of HCl particles in a given space, the greater the rate of reactivity to provide more product of Carbon Dioxide in a given time.
Experiment 2: Collecting Carbon Dioxide gas over water
These results also clearly show that the reaction rate increases if the molarity of the acid has been increased. The time taken to collect 100cm3 of Carbon Dioxide gas in standard conditions, over water increases as the concentration of the hydrochloric acid is decreased. This is an inverse proportion. The results which I obtained in this experiment were sufficient showing a good curved line of best fit. The two attempts show the same trend as illustrated by the graphs. The processed results in the form of an average give a very similar graph given by graph three on page 21. With fewer HCl particles in a given space, there are less successful collisions giving rise to Carbon Dioxide production in a given time.
Experiment 3: Collecting Carbon Dioxide gas in syringe
Collecting Carbon Dioxide gas in a syringe was a very similar experiment to Experiment 2 - (Collecting Carbon Dioxide gas over water), but was much more accurate providing better results and excellent graphs. The results in this experiment again clearly show as the others, the reaction rate increases if the molarity of the acid is increased. The points made on the scatter graph has given a very accurate line of best fit, where the gradient was much steeper in the first two concentrations which where 2M and 1.5M. I again carried out the experiment twice and used the average out of the two, to get a more reliable set of results. The processed results in the form of an average give a very similar graph to the first two attempts. This shows that there was a very little error between the two experiments and shows that the experiment was very accurate. The increase in the concentration clearly shows the increase in the number of particles colliding into each other.
CONCLUSION
In conclusion I can clearly state that in all three of my experiments, the results given where very sufficient showing trends in clear and precise graphs. I started of the investigation by carrying out the "counting bubbles" experiment which very well unlike what I predicted. This experiment successful as it showed a good trend in the graph, although I cannot conclude this experiment by saying that it was "accurate" as there may have been many errors in counting the number of bubbles. When counting the bubbles I had to continuously count for up to 5 minutes and I had to concentrate very hard. This experiment was not very good although I managed to get good successful results. My second experiment was of "Collecting Carbon Dioxide gas over water". This experiment was better and more accurate than the previous one. In this experiment I was measuring the time taken for a measuring cylinder to fill up with 100cm3 of Carbon Dioxide gas. This again gave sufficient results and graphs as well as being a successful experiment. In this experiment there may have been errors actually due to the apparatus used and the way that they were set up. The way it needed to be set up to be able to displace water was difficult to set up as it was fiddly to turn the measuring cylinder full of water up side down and then to get a delivery tube underneath it. As it was difficult we probably made some mistakes in starting timer on time and stopping it so made the results a bit wrong. Experiment 3 - "Collecting Carbon Dioxide gas in a syringe" was my final and the most accurate experiment out of the three giving tremendous results and graphs. I was measuring the time taken for the syringe to fill up with 100cm3 of Carbon Dioxide gas. This was very similar to experiment 2 but the equipment used in this experiment were less fiddly and gave much more accurate results with an excellent graph. The pattern in this experiment shows that when the reaction first starts, the reaction is fastest, from then on, the reaction slows. We can see this because the gradient of the curve is steepest at the beginning.
I repeated all 5 concentrations twice to be sure that they were reliable results and in all cases the higher the concentration the higher the rate of reaction. During the whole experiment, it has always been a fair test, which helped in getting good results. You can clearly tell that experiment 1 is not so accurate as for 0.1M there in no bubbles produced which indicates that no reaction has taken place, where as in experiment 3 you can clearly see that there is some kind of reaction going on for 0.1M. I also used distilled water in all my experiment to show that marble chip doesn't react with distilled water at all but 0.1M does react even though it reacts very slowly.
I noticed that during the experiment the amount of gas it was producing would slow down, this is because the activation energy which it had been given at the start gave it a 'boost' and at this point it would have been the fastest, until it had worn off which would be in the middle. The particles of acid and Calcium Carbonate react and give the acid energy to move about and collide with the CaCo3. In the graphs, I saw definite patterns; they all have the same trend and the graphs shown on experiment 2 & 3 have curved line of best fit. In experiment 3 the gradient is much steeper for 2M and 1.5M than it is in experiment 2. This shows that there is a faster rate of reaction in a given amount of time.
By predicting that all three experiments will show a trend in the graphs if carried out successfully, I was absolutely correct. I also had predicted that experiment three will give the best and most accurate set of results and graphs with steep gradients. I was again right and my prediction matched my results and graphs. "Higher the concentration the higher the rate of reaction." I had stated this in all my prediction. This prediction was one that occurred in all three experiments and again was proved correct. However I also stated in my prediction that if I doubled the concentration from 1M to 2M hydrochloric acid then the rate of reaction will also double. I have discovered that this is not the case. My original prediction was that the initial rate of reaction would double as the concentration doubles. This was incorrect because it was not based on experimental evidence.
I have written in my scientific knowledge that when you increase the concentration of the acid there are more particles available and so there would be a more likely chance of a collision taking place, and so the reaction rate would be faster with more collisions taking place. This shows that the results that we have achieved are correct because it is a fact that as you increase the concentration of the acid the more violently it will react with the marble. The collision theory explains why an increase in the concentration of reactants will tend to an increase in the rate of reaction. The theory also explains that the grater the number of collisions, the higher the chance that some of them will be effective. Also the higher the concentration the greater the number of atoms in the solution, therefore a faster rate of reaction. As two molecules collide, they slow down and their kinetic energy is converted into potential energy and so they begin to climb the activation energy hill. In higher concentrated solution of hydrochloric acid there are more particles present and therefore there are more particles that are likely to overcome the activation energy barrier and so the reaction would be much faster.
Looking at the results obtained in my tables and graphs I have noticed that my predictions are mostly correct; increasing the concentration of Hydrochloric acid does increase the rate of reaction with Calcium Carbonate. Taking all that has been mentioned I can finally conclude that as the concentration of Hydrochloric acid increases the faster the amount of Carbon Dioxide will be produced and therefore the faster the reaction.
EVALUATION
My investigation on the rate of reaction was very successful. I investigated the factor concentration out of the four factors. I investigated how the concentration of hydrochloric acid affects the rate of reaction with marble chips. To investigate the different concentrations I did 3 experiments the first was "Counting Bubbles", the second was "Collecting Carbon Dioxide gas over water" and my third and the final experiment was "Collecting Carbon Dioxide gas in a syringe". My first experiment was to count the number of bubbles given off in a reaction for every 1 minute for up to five minutes with different concentrations of acid. In experiment 2, I was measuring the time taken to displace 100cm3 of water by Carbon Dioxide with different concentrations. My third experiment was to collect and time how long it takes for 100cm3 of Carbon Dioxide to collect in syringe with different concentrations of acid.
All three experiments that I carried out gave sufficient results and graphs to prove my prediction which was that as the concentration is increased, so will the rate of reaction. All three experiments that I carried out went satisfactorily although two of them weren't very accurate. Experiment three, which was "Collecting Carbon Dioxide gas in a syringe", was the most accurate and gave the best graphs and results out of the three experiments that I carried out. Counting bubbles was an experiment that was unfair and inaccurate as we had to count bubbles at different speed for up to five minutes. When counting bubbles, I may have made mistakes by miscounting some of the bubbles. This was very unfair and so did not give me accurate results, although they were sufficient to prove my prediction and give a good table of result and graphs. "Collecting Carbon Dioxide gas over water" was a good and fair experiment for this kind of investigation although it was not totally accurate as the equipments used were fiddly. What I mean is that the way it needed to be setup up to be able to displace the water was difficult to set up as it was fiddly to turn the measuring cylinder full of water upside down. The setup of this experiment was a bit difficult although I did manage to get sufficient results but not very accurate. I had predicted that as the concentration will double, so will the rates of reaction. The experiment proved that I was wrong although I was correct that as the concentration is increased, the rate of reaction will also increase. The third experiment that I carried out was "Collecting Carbon Dioxide gas in a syringe". This experiment was very easily setup with the appropriate equipment. This experiment was much more accurate than the other two experiments and also gave very good results. The graphs produced from the results were excellent giving a steep gradient at the start but gradually the gradient changed for the curve to become towards a vertical line. The experiment gave excellent results that were very accurate results and they also confirmed my prediction which was: as the concentration is increased the rate of reaction will also increase. All the experiments weren't absolutely accurate, although they all gave very good results and graphs to make a firm conclusion for this investigation.
I would say from this investigation that the most reliable experiment to test the rate of reaction, with hydrochloric acid and marble would be "Collecting Carbon Dioxide gas in a syringe". This is because it gave the most accurate results out of the three experiments that I tried. The equipment used was also very easily setup and sufficient to use. This made the experiment straight forward and accurate to carry out. If I was to carry out this investigation again, I would definitely not carry out experiment 1 (Counting Bubbles) again because no matter how many times you do the experiment the results are never going to be fair. I think to improve the procedure used in experiment 2 (Collecting Carbon Dioxide gas over water), I could have when turning the cylinder full of water up side down, put a plastic piece on the bottom of it to stop the water from escaping the cylinder. By doing this I think I would get much more accurate results and graphs that would confirm my prediction. I did make one inaccurate prediction which was that, as the concentration is doubled so will the rates of reaction. This was incorrect because it was not based on experimental evidence. .I evaluate that the experiment was successful and got reliable results. Although there was space for improvement, the resources available for the experiment was limited, therefore I was not able to use sophisticated devices. I think for the third experiment there was no way of improving it as it was very straight forward and the method gave good sufficient results and graphs. It was clearly the best experiment to be carried out for this investigation out of the three. During the whole experiment, it has always been a fair test, which helped in getting good results.
I generally enjoyed the experiment very much as it was carried out very successfully. The results from the experiment illustrated in the graph seem rather accurate. I am glad to say that the errors of the experiment were caused by limitations beyond my control and so I did not perform poorly. I ensured the test was as fair as I could possibly make it and conducted safely by demonstrating the statements in my plan.
From this investigation I have learnt all about chemical reactions that include the way in which they can be altered to change their rate, the theory of kinetics and its connection to the rate of reactions.
In this whole investigation I have used hydrochloric acid as an example of acid rain. The investigation it self began by speaking of the Taj Mahal being made of marble and the fact that it was wearing away due to the effect of acid rain. On analysis of rain it is unlikely that there would be a high concentration of Hydrochloric acid. Instead I would expect to find a mixture of carbonic acid from Carbon Dioxide, Sulphurous acid from Sulphur Dioxide, Nitric acid from Nitrogen Dioxide and possibly Sulphuric acid that may have been oxidised from Sulphurous acid. It would be interesting to extend this investigation by studying the effects of these individual acids on marble. I have read in a book entitled "A new chemistry" that Sulphuric cid would convert the surface of marble into calcium sulphate. This substance is used to make plaster of Paris and that has the effect of sealing up marble as it is almost insoluble in water. In other words it might be able to protect the marble of the Taj Mahal instead of eroding it. That might be a good thing!
BIBLIOGRAPHY
A new chemistry - Clynes, Williams and Clarke - Hodder & Stoughton.
DK multimedia - eyewitness encyclopaedia of science 2.0
Microsoft's Encarta 98
World book encyclopaedia
GCSE Science class book, by David Baylis, Graham Booth and Bob Mcduell. - LETTS
GCSE Science (double award) - A Revision Guide by Dr. Ron Joyner
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