Analysing results
The average results for each temperature were considered in turn, plotted on a graph, and a line of best fit for each temperature was drawn.
Table of average results (in minutes and seconds) for each temperature
The results showed that the reaction between dilute hydrochloric acid and calcium carbonate occurred fastest at the highest temperature (70ºC). This was shown by the fact that 100ml of one of the products of the reaction (CO2 gas) was collected in the shortest time when the temperature was 70ºC. The longest time for this amount of gas to be collected occurred at the lowest temperature (20ºC). As the temperature of the reaction was increased, so the speed at which the reaction occurred also increased, through 30ºC, 40ºC, 50ºC and 60ºC (see first graph)
However, in order to fully compare my results with my predicted graph, I need to convert my results so that the time increases as a constant from 30 seconds to 6 minutes and then, from my original results, adjust my volumes of carbon dioxide accordingly. This gave me the following table of results.
Average table of results 2 showing amount of CO2 collected in mls:
From the table above, graph 2 was drawn.
Using graph 2 it is possible to calculate the rate of reaction for each temperature as follows: (The amount of carbon dioxide given off between 30 seconds and 1 minute 30 seconds was used to give a fair comparison. This was not possible at 70ºC because of the speed of the reaction.)
20ºC rate of reaction = gradient = 18 – 6mls =12ml/min
1.5 – 0.5min
30ºC rate of reaction = gradient = 32 – 10mls =22ml/min
1.5 – 0.5min
40ºC rate of reaction = gradient = 53 – 12mls =41ml/min
1.5 – 0.5min
50ºC rate of reaction = gradient = 68 – 20mls =48ml/min
1.5 – 0.5min
60ºC rate of reaction = gradient = 108 – 35mls =73ml/min
1.5 – 0.5min
70ºC rate of reaction = gradient = 100 – 50mls =100ml/min
1.0 – 0.5min
From the rate of reaction results it is possible to see that the reaction rate increases as temperature increases. The rate of reaction increased most between 60ºC and 70ºC and least between 40ºC and 50ºC.
Conclusion
My prediction stated that there will be a positive correlation between the rate of the reaction and the temperature so that as the temperature is increased, the rate of reaction will increase. My results proved this prediction correct as, for example, after 1 minute the amount of gas given off was:
At each 10ºC increase, the rate of reaction increased as more gas was given off at each increase of temperature.
This is because the reaction needs energy so that original bonds are broken and new bonds can be formed. If the collision has enough energy then the reaction takes place. The more successful collisions there are, the faster the reaction. The more the particles are heated, the faster they move, the more chance there is of particles colliding and the reaction taking place. Therefore, at 70ºC the particles are moving faster and there is more chance of them colliding and when they do collide they are moving faster so the more chance there is of the reaction taking place. It is not only necessary for particles to collide, but also that the collisions have enough energy. Heat provides extra energy, causing particles to both move faster and collide more successfully.
I expected my second graph to show a levelling off at each temperature over a period of time as more atoms and particles were used up during successful collisions. However, this change in rate of reaction as the reaction proceeded was not apparent and my graphs showed straight lines for each temperature when I plotted my lines of best fit. This is likely to be because of the relatively small amount (100mls) of CO2 collected (see evaluation) which did not allow each reactant to be used up and all possible collisions completed.
Evaluating evidence
I think the results I collected are sufficient to support a firm conclusion but the reliability of a small amount of the data was in doubt. At 30ºC, trial 3 had to be ignored in the final average as an anomalous result. This could be due to experimental error. It may have been that the temperature was slightly higher than 30ºC giving a faster result. It may have been that because the results were cumulative, the stopwatch was started too soon leading to each results being inaccurate.
To improve the accuracy of the experiment, instead of leaving the acid for 5 minutes to warm up, I would measure the temperature of the acid and start the experiment when it gets to the correct temperature. This will make the experiment more accurate as I will know the acid has changed to the correct temperature.
I would also take a wider range of readings, both of temperature e.g. 10ºC and 80ºC and increase my trials from 3 to 5 to give me a more accurate average. I could also have used a more accurate measure of marble chip by weighing each one.
If more time had been available, I would have allowed each reaction to be completed i.e. waited until all of the carbon dioxide had been given off, so that I could see if the reaction rate for each temperature got slower over time. In order to do this, I would need to change the apparatus i.e. use a larger syringe to collect the gas as the size of the original syringe (100ml) was a limiting factor.
Bibliography
Cox, Michael C. (1990) Chemistry A level and AS level, Longman Group Ltd.
Gallagher, RM Ingram, P (1997) GCSE Chemistry, OUP
Lowrie, RS Ferguson, HJC, (1975) Chemistry, An Integrated Approach, Pergamon Press
An investigation into how concentration affects the rate of a chemical reaction
An investigation into how concentration affects the rate of a chemical reaction
Background information
To investigate how concentration affects the rate of reaction we will be reacting calcium carbonate and hydrochloric acid. To make this a fair test we will have to keep all variables the same except the one we area investigating. The products of the reaction between calcium carbonate and hydrochloric acid are calcium chloride and carbon dioxide. To measure the rate of reaction we will be measuring the volume of carbon dioxide produced. The size of the marble chips available will be small, large and medium. The highest concentration available in the experiment is 2 molars.
The equation for this reaction is:
CaCo3 + 2HCL CaCL2 + H2O + CO2
Variables
The variables that may have an affect on this experiment are:
Size of marble chip- the size of the marble chip will affect our experiment because this dictates the surface area. The larger the surface area the more acid that will be in contact with the hydrochloric acid and able to react.
Concentration of hydrochloric acid- this is the proportion of hydrochloric acid in the solution.
Volume of acid- this will be the amount of hydrochloric acid that will be reacted with the marble chips.
Catalysts- by weakening bonds these increase the rate of reaction by lowering activation energy a catalyst will not be used in this reaction, however.
Mass of marble chips- The mass of the marble chips is a way of measuring the quantity of chips being used.
Temperature- the temperature adds energy to the reaction an affects how quickly the particles move. By doing this temperature affects the number of affective collisions
Light intensity- the light intensity has a very small affect on the experiment so will not be measured in this experiment.
Outline Plan
· We have chosen to investigate how concentration affects the rate of reaction
· We will make sure our method is safe by wearing safety goggles and following safety procedures carefully
· I have explained what I think will happen in this experiment by using scientific knowledge in my prediction
· To make this a fair test I will control the variables I am not investigating and to find these values I have carried out preliminary experiments.
Safety
To make sure we are safe in the lab here are some of the things we will do in more detail.
· Wear safety goggles because we are dealing with a bleach
· Tuck stools in to make sure mo-one falls in the lab
· Put all bags under the table to make sure no-one falls
· Never run in the lab
· Always stand up when carrying out experiments so we can move away if we are in any danger
Prediction
I predict that the higher the concentration the faster the reaction will take place this is because in a higher concentration there will more hydrochloric acid molecules per set volume. This means that there will be a higher chance of the calcium carbonate molecules colliding with the hydrochloric acid and reacting. This should in theory increase the rate of reaction as the concentration is increased.
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.
The increase in the concentration should be directly proportional to the increase of the reaction rate at a given time. This is because by doubling the number of hydrochloric acid molecules present the chance of a collision should be doubled, as there is now twice the possibility of a collision-taking place initially. This can be thought of as like people in a refined space, if there are twice the number of people there will be twice the chance of people colliding. This situation may change over time, however, depending on the situation.
This shows how a higher concentration produces more collisions.
Activation energy should not be changes in this experiment though as the same amount energy will be required to break the bonds. This is because each particle has the same amount of energy the only reason the reaction is faster is because there are more particles. This means activation energy will not have an effect on this experiment.
Measurements
To make this experiment a fair test we will keep all values we are not investigating the same. To decide on the values of variables we will keep the same we have carried out preliminary experiments.
The first preliminary experiment we carried out was to find the mass of chips to use and this experiment was also used to test the range of concentration to use in the experiment. These experiments were important to carry out because we could make sure the reaction did not fill up the cylinder too quickly leaving many times blank as the cylinder cannot contain all of the gas. This could also make sure the reaction did not take place too slowly to give us a small range of results.
To carry out the experiment we used a gas syringe and timed how long it took for the syringe to be filled. The volume of the syringe was one hundred cm³. We reacted both of the reagents in a conical flask and measured the mass of the chips on a electronic balance to get a fairly accurate reading.
Our results are shown underneath.
From this we decided the best mass to use was 7.5 grams this was because this reaction took place at a reasonable rate because it was fast enough to get a wide range of results but anything faster would make the experiment hard to record as the cylinder would be filled too quickly.
We also found from this these were the best range of concentrations to use because the times were the extremes were high enough and low enough to get a wide range of results.
The values of all the other variables are:
Equipment
100cm³ Conical flask- this will be used for the reaction to take place because it is large enough to hold the reaction
Measuring cylinders- because these are different sizes so it will enable us to measure higher volumes
Clamp- this will help to help the hold the cylinders so we can concentrate on recording the results
Container- we will use this to put the cylinder of water upside down in so water does not spill
Delivery tube- this will be used for the gas to travel down and will be useful because we will not have to hold the conical flask.
Stopwatch- this is needed to measure when the volume of gas needs to be recorded.
Range of numbers and readings
In this investigation we will be recording the volume of gas every twenty seconds because this was a suitable time interval for finding a measurable change to take place. The time we will be measuring this experiment for is two minutes because this gave us enough data for us to draw an accurate graph and we would not have to wait too long to complete one experiment. This gave us time to repeat the experiment three times so we would have more accurate averages. We will be measuring the cylinder to the nearest cm³ because this is how often the cylinder is marked so this is the most accurate we can get. The time will be measured o the nearest millisecond we will not be able to record the volume at exactly this time though so we will probably measure the time to a two second accuracy.
Method
To make the test a fair test we had to carry out the same method each time this is what we did.
First we filled the tub with tap water about half way up and filled the measuring cylinder with water and then turned the measuring cylinder upside down into the tub of water so the cylinder was still filled with water. By doing this we did create a slight margin of error because some of the water was displaced when doing this although it was very little. Then we clamped the measuring cylinder in place. We changed the size of the cylinders, however, this did not make the test unfair. We then 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 now measured the volumes of each in a measuring cylinder to be accurate. To make sure the mass of marble chips were right we measured on the electronic balance to one decimal place. Then we put the chips and the acid in the conical flask and started the stopwatch.
As the experiment has started we now recorded the volume of gas every twenty seconds. We did this until two minutes had elapsed. We then changed the mass of the chips and the concentration of acid until we had all the data that was required. While doing this experiment we had to work carefully to avoid accidents and follow safety procedures.
Underneath is a diagram of how the experiment was set-up
To find out information for my investigation I used the resources listed below.
Internet- www.about.com
www.excite.co.uk
Books- Nelson Science
Collins science
Obtaining evidence
While working all safety procedures were followed very carefully like the use of safety goggles and putting the bags under the table. The measurements I feel were fairly accurate as the results were what was expected. There was one anomalous result, however, which was repeated to get a more accurate result. We repeated the experiment three times so we could find averages and get more accurate results. The results were measured to the nearest centimetre cubed because this was the maximum accuracy of the cylinders. The results show the results we got for each experiment.
* Anomalous result repeated above (experiment four)
Analysis and Conclusions
By doing a calculation similar to underneath all the results from the same concentration were added together and divided by three (the number of experiments). The anomalous result was not included in this, however, but the repeated result was.
To find the mean this calculation was used
first result + second result +third result
3
The mean results are
From these results we can conclude that by increasing the concentration of hydrochloric acid the reaction rate is increased. This can be seen as the highest concentration had the highest reaction rate and reached 260 cm3,where as the lowest concentration only reached a maximum of 29 cm3 at the end of the two minutes. The increase does seem to be proportional, as the gradient of the line seems to decrease by roughly the same amount each time. This is shown underneath.
To calculate the gradient the method below was used.
Point on Y-axis
Point on X axis
From this the following Gradients were found
Concentration molars Gradient
2.0= 2.3
1.6= 1.9
1.2= 1.5
0.8= 0.9
0.4= 0.2
The results that were found were what was expected to a certain degree. The reaction rate did not seem to show any signs of slowing down though which is what was expected. This was probably due to the fact that the experiment was not times for long enough though.
The fact that the reaction rate was highest at the highest concentrations shows that the higher the concentration the more particles that are present per set volume which shows increases the rate of reaction. This was not exactly followed in the experiment, which was probably due to a margin of error in the results, but the pattern was still showed. This also proves tat activation energy does not play a part because if this did the gradients of the lines would not increase by the amounts they did. This is due to the fact more/less energy would be needed to start the reaction and there would be a higher or lower gradient of the line so the gradients would not go up /down by the same amounts.
Evaluation
The results that were derived from the experiments showed a pattern but the prediction that was made was not completely supported because the reaction rate did not shown any signs of slowing down. There was one anomaly, however, but this experiment was repeated to give results that matched the pattern. It is not certain why this result was found but it was probably due to the mass of the marble chips being measured slightly inaccurately because we measured the mass of the chips to the nearest whole number this would account for a slight margin of error. Another possibility is because the surface was different for each chip the total surface area was different this would be very unlikely, however.
The measurements were accurate to about cm³ because this how often the cylinders were marked.
The method did show the relationship between the concentration and the rate of reaction but there was a slight margin of error because when turning the cylinder upside down a small volume of water was lost. To solve this problem we could use a gas syringe but the problem with this is we could not test the higher volumes of gas, which would mean the range of results would be lower which would mean the pattern we got would be less obvious.
The experiments were fair tests to a certain extent but there was a certain margin of error because the results recorded were only to the nearest cm³ and the values of the controlled variables were not exact amounts so the may have been slightly differently each time which would have affected slightly the reliability of the results. This would have made little difference to the results though as the volume of gas was only measured to the nearest cm³.
To find if the prediction was supported or to find if the reaction rate did slow down after the time progressed the experiment could be timed for longer than two minutes. This would also enable us to find weather the pattern changed after a certain time or the reaction rate just generally slowed down and we found a curve when comparing the concentration of the acid and the calcium carbonate.
It was also not certain if the concentration keeps increasing the rate of reaction or this only happens to a certain extent. This could be found out by extending the range of concentrations reacted. These reactions would have to conducted very carefully though as hydrochloric acid of this concentration can be very dangerous.
Marble Chips and HCL
Aim
The aim of this experiment is to find out how different variables affect the rate at which the reaction between Marble chips (CaCO ) and Hydrochloric acid (HCl) takes place. There are many variables that effect the rate of this reaction such as the following:
1. Temperature
2. Concentration (Pressure for gases)
3. Catalyst
4. Surface area
In my investigation I will be testing how changing the concentration of the Hydrochloric acid, the surface area of the marble chips and the temperature have an effect on the speed of the reaction. I will do various experiments and then evaluate the results and come to a conclusion.
The reaction that will take place is
Hydrochloric acid + Calcium Carbonate
Calcium Chloride + Water + Carbon dioxide
Introduction
Collision theory - Collisions between reactant particles are needed for the reaction to take place in order to form a product. Some collisions are successful and give a product while others don't because particles don't have enough energy.
Activation energy - The amount of energy needed for the reaction to be started. If there is enough energy then the reaction takes place and a product is formed, but if there isn't enough then no reaction takes place.
There are two possibilities for increasing the rate of reaction:
1. The activation energy is reduced so that there is a better chance of particles having enough energy to react. Reactants will need less energy to react.
2. The number and strength of collisions is increased so that the reaction can
happen faster. If the particles have more energy then more particles will be able to react.
Solid reactants like marble chips are effected by surface area, the larger the surface area the more collisions that will take place. This will increase the rate of reaction and decrease the time taken.
Liquid/ Aqueous reactants rely on collisions for more collisions to take place. In a concentrated acid solution there are more acid particles so more collisions will take place. There will be an increase in the product formed in a certain time.
When the temperature is increased, the particles will have more energy, so they will move faster. This will result in the particles colliding more frequently and increasing the speed of the reaction. Also when they have more energy there will be more chance of the collisions being successful because the activation energy will be attainable.
The addition of a catalyst will reduce the activation energy and makes more successful collisions. The reaction will be faster but the catalyst will not be used up during the reaction. When the activation rate is lower not much energy is needed to make the reaction successful.
Concentration
Aim
The aim is to find out if changing the concentration of the hydrochloric acid solution has an effect on the time taken for the reaction
Prediction
The more concentrated the acid then the quicker the reaction will take place, because there will be more HCl particles than water particles for the marble chips to collide with and therefore react. More collisions between the two reactants (HCl and CaCO ) will take place resulting in a quicker time for the reaction.
I predict that if the concentration of the HCl is doubled then the experiment will happen twice as fast. This is because twice as many HCl particles will be present than previously and there will be twice as much chance of the calcium carbonate chips colliding with the concentrated hydrochloric acid. Therefor when the concentration is double the time take for the reaction should be halved.
Variables
Independent - Concentration of the Hydrochloric acid solution
Dependent - The amount of CO produced
Control - Temperature, Surface area, Amount of HCl , Mass of marble chips
Apparatus
The solutions with different concentrations of acid have to be prepared before the reactions can start. The solution has to have a total volume of 10cm . The following solutions should be prepared by mixing water and the acid in a set ratio.
HCl H O
10 0
9 1
8 2
7 3
6 4
5 5
4 6
3 7
2 8
1 9
When the solutions have been prepared the apparatus has to be set up. The following equipment will be needed for the experiment.
Hydrochloric acid
Water
Calcium Carbonate chips
Conical flask
Glass capillary
Syringe
Rubber bung
Spatula
Clamp
Stand
Measuring cylinder
Stopwatch
Top pan balance
Method
When the apparatus has been set up as shown above, 10 cm of the acid solution will be measured using a measuring cylinder. This will be poured into a conical flask. 3g of powdered CaCO chips will be weighed out using a top pan balance. This will be put into the conical flask and the rubber bung attached to the syringe will be put over it immediately afterwards. At the same time the stopwatch will be started.
After every ten seconds the amount of CO released will be recorded by looking at the measurement on the syringe. This will be done for 100 seconds so by the end of the experiment 10 readings should be obtained.
The experiment will be repeated and carried out in the same way, only the concentration will be changed. A less or mare concentrated solution will be used but the total volume of the solution will stay the same.
Surface area
Aim
The aim of this investigation is to find out if the surface area of a calcium carbonate chip has an effect on the time taken for the experiment.
Prediction
The increase in surface area will result in a faster reaction. If the marble chips are powdered then the reaction will happen faster because more of the chip will be exposed to the acid and they will react quickly
When the surface area of the calcium carbonate chips is doubled there will be twice as much chance of it colliding with the Hydrochloric acid. Therefore I predict that when the surface area is doubled, the time taken for the experiment is halved.
Variables
Independent - Surface area of the marble chip
Dependent - the mass loss of the solution
Control - Temperature, Concentration, Amount of HCl , Mass of marble chips
Apparatus
Two experiments will be carried out, the first one will have marble chips from essaybank.co.uk with a large surface area and the second one will have marble chips will a small surface area. These will have to be prepared, the marble chip with the large surface area has to be crushed and the other one will be large blocks of the marble chip.
When the marble chips have been prepared the following apparatus has to be set up. The following equipment will be needed for the experiment.
Calcium Carbonate chips
Hydrochloric acid
Water
Top pan balance
Conical flask
Spatula
Measuring cylinder
Stopwatch
Method
When the apparatus has been set up as shown above, 25 cm of 2 M acid solution will be measured using a measuring cylinder. This will be poured into a conical flask. The Calcium Carbonate chips that have a large surface area will be taken and weighed out, 5 g will be taken. The all the contents will be weighed on the top pan balance and the solution will be left on the top pan balance even after the reaction has started. This is because the weight loss due to carbon dioxide being released has to be measured so that a conclusion can be made on the most affective surface area.
When the experiment has started the mass of the solution will be recorded every 30 seconds. This will be done for minutes so by the end of the experiment 20 readings should be obtained.
The experiment will be repeated and carried out in the same way, only this time the other marble chip will be used, the one that has a small surface area. All other variable will be controlled to make sure the experiment is fair.
Results
Time Weight (g) Weight loss (g)
(mins)
0.0 100.0 100.0 0.0 0.0
0.5 99.3 100.0 0.7 0.0
1.0 99.0 99.8 1.0 0.2
1.5 98.7 99.7 1.3 0.3
2.0 98.6 99.6 1.4 0.4
2.5 97.7 99.4 2.3 0.6
3.0 97.5 99.4 2.5 0.6
3.5 97.4 99.3 2.6 0.7
4.0 97.4 99.2 2.6 0.8
4.5 97.2 99.1 2.8 0.9
5.0 97.2 99.1 2.8 0.9
5.5 97.2 99.0 2.8 1.0
6.0 97.1 99.0 2.9 1.0
6.5 97.1 99.0 2.9 1.0
7.0 97.0 99.0 3.0 1.0
7.5 96.9 98.9 3.1 1.1
8.0 96.9 98.8 3.1 1.2
8.5 96.9 98.8 3.1 1.2
9.0 96.8 98.7 3.2 1.3
9.5 96.8 98.7 3.2 1.3
10.0 96.8 98.7 3.2 1.3
I found that the marble chips of large surface area reacted straight away, but as time went on the reaction slowed down. But with marble chips of small surface area the reaction process stayed constant throughout the experiment.
After the powder marble chips were poured into the conical flask the reaction started straight away but slowed down after just 1second. The fastest rate of the reaction was in the first second.
The experiment was a success. When I done this experiment I found that surface area is a factor that affects the rate of reaction. As I increased the surface area of the calcium carbonate (i.e. made the pieces smaller), the rate of the reaction was increased (the reaction was faster).
Temperature
Aim
The aim of this experiment is to observe whether the temperature of the solution has an effect on the time taken for the experiment.
Prediction
If the temperature at which the reaction takes place is increased then the reaction will be faster because the particles will have more energy and therefore collide more often.
A temperature increase of 10 C will see the time taken for the experiment halved because energy of collisions in the particles increases, this means that there are going to be more successful collisions.
Variables
Independent - temperature of the solution
Dependent - amount of carbon dioxide gas collected
Control - Surface area, Concentration, Amount of HCl , Mass of marble chips
Apparatus
Sodium thiosulphate
Hydrochloric acid
Top pan balance
Conical flask
Spatula
Measuring cylinder
Stopwatch
Bunsen burner
Thermometer
Tripod
Paper
Marker (dark coloured)
Light (match, spark)„«
Method
For this experiment I will be using I will set up the apparatus as shown above. I will then get the sheet of paper and using the marker, I will draw a large cross on it. Measure out 50cm3 of sodium thiosulphate using the measuring cylinder. Once this is done pour it into the conical flask. Place the conical flask on the tripod and using the Bunsen burner heat the conical flask containing the sodium thiosulphate, put a thermometer inside and wait until the reading on the thermometer is at the required level.
I will then place the conical flask on the piece of paper with the cross. Now measure 5cm3 of the hydrochloric acid and pour it into the test tube. Pour the acid into the conical flask and start timing straight away. Wait until the cross cannot be seen any more and stop the timer. Repeat this for all the measurements 10, 20, 30, 40, 50 and 60 degrees Celsius. The experiment will be done three times and the average will be taken from all the results.
Results
Temp CO gas
( C) set 1 set 2 set 3 average
10 12 10 14 12.0
20 23 25 18 22.0
30 40 38 41 39.7
40 70 72 69 70.3
50 120 115 128 121.0
60 200 204 203 202.3
As the temperature got higher the rate of the reaction speeded up. The cross disappeared faster. Those of higher temperature had more carbon dioxide produced thus causing the cross to disappear.
This experiment was successful. It proved my prediction correct. As the temperature was increased so did the rate of reaction. It proved that the temperature is a factor that affects the rate of reaction.
Results
These were the results obtained after doing the experiment with different concentrations of the Hydrochloric acid.
10 20 30 40 50 60 70 80 90 100
10:00 65 82 84 100 108 110 110 110 110 110
09:01 53 72 80 84 92 103 109 110 110 110
08:02 46 61 64 71 77 81 85 92 101 110
07:03 37 48 59 65 68 70 72 73 75 78
06:04 20 30 35 41 45 50 52 56 60 61
05:05 17 25 32 36 42 45 49 52 55 57
04:06 11 15 21 26 31 35 40 45 48 51
03:07 9 13 19 22 25 27 31 34 35 36
02:08 5 11 15 19 23 25 27 29 31 31
01:09 3 7 13 15 16 17 19 22 23 25
I found that as I increased the concentration of the acid, there was more reaction and a faster reaction. Hence more hydrogen gas produced. By looking at graph, line for the least concentrated solution was the least steep and this meant it was also the slowest.
The experiment was a success. When I done this experiment I found that concentration is a factor that affects the rate of reaction. As I increased the surface area of the calcium carbonate (i.e. made the pieces smaller), the rate of the reaction was increased (the reaction was faster
GCSE Chemistry - Limeston Chips Coursework
Carbonates react with strong acids to give off carbon dioxide and water. Marble is calcium carbonate and thus behaves in the same way:
CaCO3 (s) + 2HCL (aq)  CaCL2 (aq) + H2O (l) +CO2 (g)
In this experiment, I am going to see if temperature affects the reaction rate between marble chips and hydrochloric acid by timing the release of carbon dioxide in the reaction.
I predict the higher the temperature, the faster the reaction rate. This is due to the kinetic theory. The more heat that is given to matter, the faster the particles move. This happens in the acid, so the faster the particles move, the faster the reaction rate due to more collisions between the marble chips and the acid.
To help me plan out an adequate experiment and to find a suitable reading range, I will do a small preliminary experiment. Here is what apparatus I will use:
(Draw Apparatus)
I will wear goggles due to the fact that I am handling acid. I am going to take 3 readings in this preliminary experiment to see if the experiment works and takes place inside a suitable time range. I used 5g marble chips and 50ml hydrochloric acid. I am going to take readings from the top of my approximate range and from the bottom. I will also take one in the middle. This will help me to see if my range is appropriate.
I heated up the acid in the conical flask first until it reached the desired temperature. Next I placed the marble chips in and the delivery tube. I then timed how long it took to collect 50cm cubed of air in the burette. Here are the results of the preliminary.
(write or make up results)
I was careful to make this a fair teat by keeping all variables (apart from temperature) constant. To keep the marble chip surface area the same, I used only large chips. I used the same acid every time to keep the acid concentration the same and always used the same amount of materials.
The preliminary showed that the experiment worked. The timeframe is not too long or short either and can be easily measured. The range is OK, but I must be careful to not go over 70ºC as I spotted some hydrochloric acid vapours, anything over 70ºC would be dangerous. I will make one adjustment to the preliminary by heating the acid separately, and then, when it has reached the desired temperature to pour it in through the thistle funnel into the marble chips. This allows me to start timing the experiment straight away and there should be more accuracy involved. The results from the preliminary fit in with my prediction although more readings are needed.
Obtaining Evidence
(draw diagram)
I set up the apparatus as shown in the diagram above. I took precautions to wear goggles because I was handling acid. I followed the steps I had laid out in the plan with the changes that I made after the preliminary. I was careful not to start timing as I poured in the acid. This is because the gas released wouldn´t be produced by reaction but the displacement of air by the acid.
To keep this experiment a fair one, I had to keep all variables apart from temperature the same. The variables were:
Amounts of materials used
Surface area of marble chips
Concentration of acid
I made sure I used the same mass of marble chips each time and the same volume of hydrochloric acid too. I used the same concentration of acid every time so the concentration is the same. To keep the surface area of the marble chips the same, I made sure all the marble chips I used were large and therefore had similar surface area.
I repeated the experiment readings twice and took the average to gain a more accurate reading and recorded my results in a table.
Temperature Time taken to fill 50cm cubed with Carbon Dioxide (secs) Average time
(°C) READING 1 READING 2 (secs)
20 35 36 35.5
30 15 17 16
40 12 10 11
50 8 8 8
60 7 8 7.5
70 7 7 7
Analysing Evidence
I used the results obtained to plot a graph of the time it took to fill 50 cm cubed with air against the temperature. The graph shows that as temperature rises so does the speed of the reaction. This is due to the kinetic theory. As temperature increases, particles speed up, this happens in the acid and so acid particles collide more with the marble particles and so the reaction happens faster. This fits in with my hypothesis too.
The graph shows a smooth curve which becomes more horizontal as it reaches the higher temperatures. This is because at what ever temperature, the reaction will never be instantaneous.
I conclude that as temperature increases, so does rate of reaction, but the reaction is never instantaneous.
(draw graph using the data given)
Evaluating Evidence
The experiment went quite well. There were no anomalous results and nothing went wrong. Although I have some ideas which may gain an even more accurate reading. Firstly, the surface area of the marble chips were not perfect. It could have been made better if I had used powdered marble chips because the surface area would have been a lot closer. (although if I did use marble chips, the concentration of the acid would have to be weaker because the reaction would be too fast.) Secondly, and inaccuracy may have been caused by the fact that the temperature may have dropped during the reactio