Investigation Into the Effect of Concentration On Rate of Reaction Between Marble Chips and Acid
Investigation into the Effect of Concentration on Rate of Reaction between Marble Chips and Acid
Preliminary Work
Before carrying out a set of experiments, I decided to do preliminary work to look at quantities and measurements, in order for my experiments to work smoothly and accurately. To do this, I tested both amounts of marble chips and amounts and concentration ranges of acid. I also experimented with different measuring cylinder sizes. I carried out a few simple experiments varying the above, and came up with the most sensible.
We began by what seemed the most practical quantities. Firstly we looked at marble chips. We took 5g as a starting example. To accompany this we looked at what would be a sensible amount of liquid to accompany it and chose 50ml. To find the right measuring cylinder to use, we set up a mock experiment and began with a 25ml measuring cylinder. We timed experiments for both the strongest and weakest concentrations of acid and recorded the following results.
50ml acid-->0ml water = 26.80 seconds
0ml acid-->40ml water = 2 minutes, 53.77 seconds
These were both practical results and so we were happy with the size of the measuring cylinder. Along with this, we also took note at how our quantities of acid and marble chips worked together and saw that they were both satisfactory. All other equipment and the set up of the apparatus were also fine and so we decided to move on to the proper experiments.
Planning My Work
For this experiment I will need to investigate how the rate of reaction of marble chips is effected by acid as well as considering other factors that my have an effect.
Aim: To find a relationship between the concentration of acid and the rate of which a reaction takes place with marble chips.
To begin the experiment, I need to look at the chemistry of marble chips (calcium carbonate) and acid and so I will begin with their equations.
Word equation:
calcium carbonate + hydrochloric acid --> calcium chloride + water + carbon dioxide
Chemical equation:
CaCo3(s) + 2HCl(aq) --> CaCl2(aq) + H2O(l) + CO2(g)
When the reaction takes place, carbon dioxide, water and salt will be produced. Out of these three, I have chosen carbon dioxide as the one to measure for my rate of reaction. This is because it will be the easiest and most noticeable to collect. By the measurement of the carbon dioxide, we will be able to accurately follow how fast the reaction occurs. Pg 190 of the 'Chemistry for you' book, shows a sensible, simple and accurate way of measuring a gas like carbon dioxide, in an upturned measuring cylinder filled with water. If we place marble chips and acid in a conical flask, the gas will bubble through a delivery tube lowering the level of water, which we will then be able to time until all water has left the cylinder.
The amount of time it takes for the gas to fill the measuring cylinder will show us how much carbon dioxide has been given off and so will show us the rate of reaction. Rate of reaction is altered by three main things. One is SURFACE AREA. This will relate to the surface area of our marble chips. The finer the chips, the larger the surface area, and so the larger the rate of reaction. However, we are intending to keep the surface area the same. Another factor is TEMPERATURE. Again, we are not going to alter the temperature. If we were to, the hotter the temperature, the faster the rate of reaction as the molecules would have more energy. The other is CONCENTRATION. This relates to the concentration of the acid and is what we will use as our variable.
The acid particles can only react with the marble chips when they collide, as seen in the diagrams.
The acid particles move randomly through the water. As you increase the concentration of the acid, there are more acid particles in the same volume. Therefore there is a greater chance of acid particles colliding, and reacting, with particles on the surface of the marble and you increase the rate of reaction.
This is what I will use in my experiment. The concentration of acid is written in Molars. For example, 1M (molar) is half the concentration of 2M. I will alter the concentration to see what effect it has on the rate of reaction.
Predictions:
I predict that when investigation the effect of concentration on rate of reaction between marble chips and acid, that an alteration in concentration will effect the rate of reaction in a pattern. As has already been explained, as you increase the concentration of the acid, there are more acid particles in the same volume and so therefore there is a greater chance of acid particles colliding, and reacting, with particles on the surface of the marble. Because of this, I will make the prediction that the higher the concentration of acid, the faster the rate of reaction with the marble chips and the faster my measuring cylinder will fill with carbon dioxide.
I also predict a more detailed pattern. I predict that the level of concentration may also have a direct effect on the rate of reaction. E.g. that if a 2M was compared with a 1M acid which is half the concentration, the rate of reaction will also be half. I will now need to carry out my experiment to test these predictions.
My Experiment
Diagram:
Apparatus:
Conical flask - to hold the marble chips and acid for the experiment
50ml measuring cylinder - to measure the volume of acid being used ...
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I also predict a more detailed pattern. I predict that the level of concentration may also have a direct effect on the rate of reaction. E.g. that if a 2M was compared with a 1M acid which is half the concentration, the rate of reaction will also be half. I will now need to carry out my experiment to test these predictions.
My Experiment
Diagram:
Apparatus:
Conical flask - to hold the marble chips and acid for the experiment
50ml measuring cylinder - to measure the volume of acid being used in the experiment. I chose 50ml volume because that is the maximum acid we will need.
Delivery tube and bung - will transport C02 given off
Weighing pot - to hold the marble chips for weighing
25ml measuring cylinder - to collect the C02 given off by the experiment. I chose 25ml because it was the most sensible size
Balance - reading to 0.01g, must be accurate, to weigh the marble chips
Water trough - to hold the water for the collection of C02
Stop clock - reading to 0.01 of a second, to accurately time the collection of C02 and the rate of the reaction
Method:
Each time the variable is altered, I shall carry out exactly the same experiment, merely with a different concentration.
* I will begin by collecting and setting up all my equipment. I need to make sure that the chonical flask is clean and doesn't have any substances already in it. The 25ml measuring cylinder needs to be filled with water. We found that if we filled a 25ml measuring cylinder, due to excess volume above the measurements, it actually held a total of 40ml. We found this by completely filling the cylinder as we would in the experiment, and then pouring this into a larger measuring cylinder and taking the reading. The cylinder then needs to be stood upside down in the trough that also needs to have an ample amount of water in. The delivery tube needs to be under the cylinder but does not yet need to have the bung in the flask.
* The marble chips then need to be weighed accurately, remembering to take into account the surface area. These can then be put into the flask.
* I will then prepare my acid to the right concentration. The amount of acid needs to be measured accurately in the separate, 50ml measuring cylinder and then water needs to be added, if required, to dilute the acid to the right concentration.
* The acid can then be added to the flask and marble chips. The bung needs to be put in the flask immediately, and as soon as this is done I will begin the stop clock.
* I will then watch the flask carefully and as soon as the first bubble comes out of the measuring cylinder, will stop the stop clock and take my reading.
This will be carried out for each experiment. In-between, it is important to rinse and dry the chonical flask and to refill the 25ml measuring cylinder.
After obtaining a complete set of results, I will then go through the process again to repeat my experiments. This will give me added information and will help explain anything out of place if necessary.
Concentrations and Readings:
I am going to carryout five experiments, and then repeat these to give me a total of 10 results, two for each experiment. The experiments I will carry out will be of five different concentrations of acid. Along with the concentrations in ml of both acid and water, I have written along with it the concentrations in molar (M). (Our original strength of acid is 2M) The concentrations will be:
Acid (ml)
Water (ml)
Calculation
Molar (M)
50
0
2 x 5/5 = M
2
40
0
2 x 4/5 = M
.6
30
20
2 x 3/5 = M
.2
20
0
2 x 2/5 = M
0.8
0
40
2 x 1/5 = M
0.4
We see that in this experiment, 2M will be the strongest acid, 0.4 will be the weakest. The way that the amount of ml is always equal to 50ml means though the concentrations change, the volume of liquid will be kept the same.
Fair Test:
It is very important to make my experiment fair. If it is not kept exact, then my results may easily be altered by slight differences that shouldn't occur.
In order to keep my experiment fair, I will ensure that there is only one variable at any time. My variable will be the concentration of acid to water. Other possible variables such as the amount of liquid, temperature, amount of marble chips or surface area of marble chips should never change and should always stay the same. To do this, we will keep the volume of liquid the same by measuring accurately in an accurate measuring cylinder. The amount of marble chips will be kept same by weighing them on accurate weighing scales. The surface area of the chips will be harder to keep accurate. We can do this generally by attempting to keep the marble chips of similar sizes as accurately as possible. I have decided to use small marble chips rather than large so that the surface areas are more similar. However, this may not always be completely accurate, and so we will have to take this into account and remember this when looking at results. We will monitor temperature with a thermometer, but will work to room temperature. We will not be able to alter the temperature as we please, and so will take a note of the temperatures for each experiment so that we can explain any changes of patterns in our results.
It is also important not to change apparatus or equipment and to keep the experiment exactly the same.
If this is kept to then my experiment will be fair, hopefully giving me the most accurate results as possible.
Safe Test:
Keeping a safe test is also very important for the safety of me and other people around me. To ensure that my experiment is safe, I will carry out the following precautions.
* Goggles should be warn to protect my eyes from acid or in case another accident occurred
* I should act in a sensible and safe manner, carefully working with the equipment and being aware of any dangers.
* The low concentration of acid I will use is a safety precaution to ensure that the acid is not dangerous.
Obtaining My Evidence
To obtain my evidence, I began by setting up my equipment and following the plan previously written. I measured hydrochloric acid (HCl) with water to produce the 50ml volume of the desired concentration, and added to this, 5g of small marble chips. I timed, in seconds, how long this took to produce a 45ml3 of gas by bubbling it through a delivery tube into an upturned mea-suring cylinder of water. The volume of which was 45ml. (All this is explained in more detailed in my plan). I included certain apparatus for accuracy. The reaction was timed accurately by using a stop clock measuring to 100th of a second. The scales measured the marble accurately by measuring exact to 0.01g. This accuracy of this was also improved by using small marble chips with more similar surface areas. The measuring cylinders used all measured to 0.1ml.
From carrying out this process, I produced a set of results for 5 concentrations of acid, 2M, 1.6M, 1.2M, 0.8M and 0.4M. I then repeated these results for even more accuracy so that I will be able to produce an average.
Results:
The results for both the first set of experiments and the repeated, second set of experiments have been combined into one table. The column of Concentration, is measured in Molars (M). This is the volume of hydrochloric acid (HCl) and water (both measured in cm3) shown together. Time 1 and Time 2 are the times (in seconds) for experiment 1, and the repeats, experiment 2.
Other information that I also took, was a note of the room temperature at the time of taking the results. The results of experiment 1 and experiment two were taken on different days and so this was important information. I already know that temperature is an altering factor in rate of reaction and so if the temperature if not the same then it is important to know so that a change in results can be explained.
Experiment 1 temperature 200C
Experiment 2 temperature 190C
The first lots of experiments were taken at a temperature 10C higher than the second lot of experiments. This needs to be known to explain any patterns that may be related.
Table of My Results:
HCl (cm3)
Water (cm3)
Concentration (Molar)
Time 1 (seconds)
Time 2 (seconds)
50
0
2
3.01
3.07
40
0
.6
7.27
3.30
30
20
.2
27.30
22.51
20
30
0.8
44.37
32.49
0
40
0.4
215.12
86.22
Analysing My Evidence and Drawing Conclusions
From my table of results, I can calculate additional information. I can work out an average time by adding the two existing times and dividing them by two. I can then find a rate of each reaction by dividing 1 by the average time. This will give me another pattern to follow by showing me how fast the reaction went at the different concentrations. The formulas for these are:
Average = time + time / 2
Reaction = 1 / time
I am going to add the answers of these as additional columns onto my table.
HCl (cm3)
Water (cm3)
Concentration (Molar)
Time 1 (seconds)
Time 2 (seconds)
Average Time (seconds)
Rate
50
0
2
3.01
3.07
3.04
0.767
40
0
.6
7.27
3.30
5.29
0.065
30
20
.2
27.30
22.51
25.31
0.04
20
30
0.8
44.37
32.49
38.43
0.026
0
40
0.4
215.12
86.22
200.67
0.005
From the table, without the average time, we can see a common difference between the time in experiment one and the time in experiment two. All results for experiment 1 are slightly quicker than the times for experiment two (with exception of the 2M experiment). We can relate this back to the temperature difference. Temperature affects the rate of reaction. When particles are heated up, they have more energy. They move around more quickly. As they travel faster, there are more collisions in a certain time. As well as this, with more energy, more collisions are likely to result in a reaction. Therefore, as temperatures are raised, reactions get faster and more likely, increasing the rate of reaction.
I noted when obtaining my results how the room temperature at the time experiment 1 was being carried out was 200C, where as experiment 2 was at 190C. This means that experiment 1, having the higher temperature, would have shown a faster rate of reaction, which is exactly what is shown in the table.
This is apart from the reading for the highest concentration, the 2M experiment. Here we see that the time in experiment 2 is faster than that in experiemnt1. However, this is by 0.06 of a second. Here human reaction time may be a factor. Although the stop clocks are very accurate, they will never be exact, as it is very hard to stop the clock exactly at the time you want it to. This error may have led to this small difference. By noticing this here, we can also take it into account for the other experiments, remembering that they are not exact but only by a very small error.
The average helps to even out the differing results which means that one, middle number is produced to work with. Because, also, I have no obvious anomalous results, readings that don't fit the pattern of the higher the concentration, the faster the reaction and so the shorter the time, the averages will follow the same trend.
To look more closely at my data, I am going to enter my average times onto a line graph. I think this is the best type of graph to use as it fits my results of continuous date and will show any trends clearly. This is on the next page (graph 1). The concentration in molars is along the x-axis, the time of the reaction in seconds is along the y-axis. I have plotted my recorded points and drawn a curved line of best fit.
From this data I can now say that the concentration does effect the rate of reaction. The line of best fit shows very clearly, a definite trend that as you increase the concentration, you decrease the time taken, showing an increase in speed. Rate and time are inversely related. As one increases the other decreases, as seen on the graph, meaning that as time increases, rate of reaction decreases.
What we see on the graph is a sharp decrease from about 200 seconds to about 50 seconds over a concentration range of only 0.3M showing fast reactions. Over another 11M there is a much more gradual decrease as it slows down, only covering approximately a range of 49 seconds. The remaining range of 2M covers 1 second and appears to be reaching a level line.
The second graph (graph 2 over the page), again a line graph, is using the rate I worked out in the table, against the concentration. This gives us I more direct trend towards the effect of concentration on rate of reaction. It shows very definitely and clearly that the higher the concentration, the higher the rate. As rate and time are inverse, I would expect an almost mirror of the concentration against time graph. This is what has happened. Instead of a sharp decrease followed by a gradual decrease as seen in the concentration against time graph, the concentration against rate graph shows a gradual increase followed by a sharp increase. My line of best fit covers 1.4M at a 0.05 rate very gradually, then a slight increase, and then over 1M, the rate increases by 0.567.
My prediction before carrying out this experiment was that the higher the concentration of acid, the faster the rate of reaction. Both these graphs prove this to be correct. This is due to the activity of the molecules in the experiment. The rate of reaction is the amount of a substance that takes part in a chemical reaction in a given time. In order to react, the particles must collide with each other. If the rate of reaction is increasing, it is the amount of particles colliding and therefore reacting that is increasing. As we increase the concentration of acid, the substance taking part in the chemical reaction (along with marble chips), the rate of reaction increases. This is because an increase in concentration increases the amount of collisions taking place. With more particles in the same volume, there is a greater and more common likely hood of collisions taking place. This is why concentration effects rate of reaction.
The second part of my prediction was more detailed. I predicted that the level of concentration may also have a direct effect on the rate of reaction, meaning that if the reaction of a 2M acid was compared with that of a 1M acid, which is half the concentration, the rate of reaction will also be half.
I looked at my graph of concentration against rate to investigate this. I used the examples of 1M and 2M and took the following readings of my graph and line of best fit.
M = rate of 0.03
2M = rate of 0.72
This shows my prediction to be very incorrect. If it would be true, then my graph would show a straight line of equal increase. However, my line of best fit gradually increases, going against my prediction.
From my results I can conclude that the rate of reaction between marble chips and acid is increased by an increase in concentration.
Evaluation
Looking back on the experiment, I think that I have carried out successful, dependable procedure that has given me precise and reliable evidence and results. First I will look at the practical work that I did. When doing the practical work, I followed my plan accurately. I kept it a safe and fair test and this is important. I experiment I planned was easy to carry out. Problems arose in temperature. The only variable was meant to be concentration, but due to uncontrollable circumstances, room temperature did alter. Luckily this occurred between sets of experiments which gave me additional information to look into. However, if that had happen part way through a set of results my results may have been slightly more irregular. To overcome this problem, results could have been taken all in one go. However, this was not practical in the spaces of time we were able to have. The other variable of surface area appeared to de successful. We already took precautions over this by using small marble chips instead of large, and so no problems arose.
The accuracy of my results is as accurate as I think I would need. From my results I have produced graphs that show very definite and visible trends and patterns and no anomalous results and so the readings must have been correct. It may be possible to improve accuracy. I learnt from the strongest concentration, the 2M acid and the fastest reaction, that for short spaces of time the accuracy is not as exact. This could be solved by an alteration in equipment. If I were to do the experiment again, I would use a larger upturned measuring cylinder. The one I used held 45ml3 of solution. I found this took roughly 13 seconds to fill with gas, making it slightly inaccurate because it was a small space of time. However, if we increase the volume of the cylinder, it would take a longer time period. This may have improved accuracy. Other equipment all proved fine. I had no troubles with any other pieces of apparatus and would not alter them.
To look into this investigation further of how concentration alters rate of reaction, I would like to look into concentration of solids in a reaction and concentrations of gases, similar to how we look at concentration of liquid and acid. It will be interesting to see if gases for instance have the same reaction patterns as liquids. I can see that my results mean that an increase of concentration of acid increases the rate. Would an increase of concentration of gas make any difference in the rate of reaction? This would help to add to an overall conclusion to the investigation.
