From there, we recorded 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 for this experiment is two hundred and forty seconds 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 also gave us time to repeat the experiment two 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 to 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 one second accuracy.
I must record the results in a table and then write it up neatly later. The factors, which may affect how well the experiment works, are how quickly the acid is put in and then the bung placed on and the stopwatch pressed. Although this is a factor, it is not really a major factor that will affect the end results, and as long as the time is kept constant throughout then it should not matter too much. Other factors that might affect the final result are what kind of water to use for dilution, I could either use water from the tap, which is not very pure (it may be too hot or too cold) or I could use distilled water.
The temperature also could affect the experiment because if heat were applied then the particles would move around more and affect the results, and then more gas would be made. I think I will need one result for each concentration and later if I need to repeat any experiments I can take an average. Some ways of having an effective experiment would be to twist the gas syringe back and forth so as to not get the syringe stuck, which could affect our results. Another thing would be to sieve the chips so to get the best marbles we can.
An important point is that I must get the right amount of acid and the same possible size and amount of marbles, because if I used about four chips, the result would end up with having too much gas being produced and the syringe will go over the 100 cm³ volume in the syringe in a very quick time, and so we will not be able to take correct readings. So to over come this problem we will test to see how many chips and at what size will be the best to use by weighing them. I must remember that if I use one chip then I must use one chip roughly the same size all the way through on all the different concentrations.
I am going to change the concentration of the hydrochloric acid to five different concentrations 100%, 75%, 50%, 25% and 0%.
I am going to do this by taking 10cm³ of hydrochloric acid away and replacing it with water.
100% = 50cm³ hydrochloric acid and 0cm³ water.
75% = 40cm³ hydrochloric acid and 10cm³ water.
50% = 30cm³ hydrochloric acid and 20cm³ water.
25% = 20cm³ hydrochloric acid and 30cm³ water.
0% = 10cm³ hydrochloric acid and 40cm³ water.
I have used one book to help me with my project; I have only used my “Chemistry For You” textbook where I got a good amount of information.
Safety:
- We must always wear safety glasses.
- I should be very careful not to drop any acid.
- Always stand up when carrying out experiments so we can move away if we are in any danger.
- Tuck stools in to make sure no-one falls in the lab.
- Put all bags under the table to make sure no-one falls.
- Never run in the lab.
7. Care in using glassware since it is sharp when broken and can cut skin.
8. Safe disposal of reagents and laboratory chemicals.
9. Care when returning all used glassware and equipment at the end of the experiment.
Fair test-
My partner and I must make sure that we use the same size, number and roughly the same mass of chips, this is because we want to keep the chips roughly the same all the way through the experiment so that it will be a fair test and the results we be in relation to each other, otherwise the results will be completely different to what we will expect and it will ruin the experiment.
We must also take our readings at the same intervals throughout the experiment i.e. I will take a reading every twenty seconds for all of my experiments.
Prediction:
I predict that the higher the concentration the faster the reaction will take place this is because in a higher concentration there will be 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.
I am saying this because of the collision theory. The higher the concentration of acid, the higher the number of acid particles there will be present per 100cm³ of acid. This means that there will be more collisions per second, which means there will be more successful collisions per second, so the rate of reaction will increase.
At high temperatures, there are more collisions per second and this results in an increase in the rate of reaction. A reaction will only occur if the colliding particles possesses more than a certain minimum amount of energy. This minimum energy for a reaction to occur is known as the activation energy (EA). The activation energy enables chemical bonds to stretch and break the rearrangements of the atom, ions and electrons to occur as the reaction proceeds. As a result of the temperature rising I predict that the particles in the marble chips receive more energy and start colliding with each other to increase the reaction, the rate of it simply depends on how hard and often the reacting particles collide with each other. The energy (gas) given off becomes more as the temperature rises, therefore I predict that the reaction using the highest temperature (100°) will produce the highest amount of gas in the slowest time. I will measure the gas by changing and controlling the rate of carbon dioxide given off during each tests.
Keeping in mind that the acid does not dissolve the marble chips it reacts with them as two separate reactants, the shape of the chips stays the same but after the experiment they cannot be used again because the acid would have used up all the reactant energy to make the gas substance. This is an exothermic reaction. I can prove that this is an exothermic reaction by measuring the finish temperatures of each of the four temperatures I have used, to see if they change or get affected by the start temperature because of how high they are; therefore the end temperature will be less than the beginning temperature.
I predict that the end temperature will become gradually more as the temperature rises because the reaction between the acid and the calcium carbonate releases heat, which gives the particles in the marble chips energy to collide. If it is releasing heat (made by the reaction) it means that a higher temperature needs to be present to make the end substance, which is the gas being made quicker, therefore the finish temperature is going to be higher than the start.
I am only going to time each reaction for 240 seconds, I went up to this point because if I go up any further I predict that it will be producing a faster rate of gas per second for me to count. After the 240 seconds it will have shown me the initial rate. I will take readings every 20 seconds, to measure the amount of gas produced, and it will also enable me to see if the reaction is slowing down or speeding up at all.
If I double the concentration of the acid from 1Molar hydrochloric acid to 2Molar hydrochloric acid then I will expect to see the rate of the reaction double. This is because there are twice as many acid particles in 2Molar hydrochloric acid than in 1 Molar hydrochloric acid, so there will be twice the amount of collisions per second and because there are twice the amount of collisions per second then there will be twice as many successful collisions per second, increasing the rate of reaction.
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 the 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 is 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.
The Collision Theory
From the kinetic theory of gases, the collision theory of bimolecular reactions in a gas phase was developed. In a reaction between two gaseous substances A&B a molecule of A must collide with B for the reaction to proceed but in a concentrated solution there will be a higher percent of reactants which will have no more energy. Not all collisions cause a reaction, only the ones which reach the activation energy of the reaction. This is why I predict that the rate of reaction will increase as the concentration of a solution increases.
In this reaction carbonate ions and hydrogen ions are colliding with each other.
Skill Area O
Obtaining Evidence.
Trial Experiment: 3.24g
50 HCl + 0 H2O
Time (seconds) Volume of gas (cm³)
20 0
40 21
60 55
80 74
100 80
120 100+
Trial Experiment: 3.31g
40 HCl + 10 H2O
Time (seconds) Volume of gas (cm³)
20 0
40 26
60 54
80 73
100 100+
Results: 3.16g
50 HCl + 0 H2O
Time (seconds) Volume of gas (cm³)
20 24
40 50
60 78
80 100
100 100+
40 HCl + 10 H2O 3.16g
Time (seconds) Volume of gas (cm³)
20 15
40 33
60 54
80 75
100 95
120 100+
30 HCl + 20 H2O 3.22g
Time (seconds) Volume of gas (cm³)
20 9
40 19
60 33
80 50
100 67
120 82
140 98
160 100+
20 HCl + 30 H2O 3.19g
Time (seconds) Volume of gas (cm³)
20 8
40 16
60 26
80 34
100 54
120 68
140 82
160 94
180 100
10 HCl + 40 H2O 3.17g
Time (seconds) Volume of gas (cm³)
20 4
40 7
60 8
80 9
100 10
120 11
140 12
160 13
180 14
200 16
220 18
240 20
260 22
280 24
300 26
320 28
Repeats:
50 HCl + 0 H2O 3.16g
Time (seconds) Volume of gas (cm³)
20 20
40 48
60 74
80 100
40 HCl + 10 H2O 3.18g
Time (seconds) Volume of gas (cm³)
20 12
40 27
60 45
80 63
100 82
120 99
140 100
30 HCl + 20 H2O 3.19g
Time (seconds) Volume of gas (cm³)
20 10
40 20
60 36
80 55
100 68
120 76
140 84
160 96
180 100
20 HCl + 30 H2O 3.15g
Time (seconds) Volume of gas (cm³)
20 8
40 16
60 28
80 32
100 58
120 66
140 83
160 94
180 100
10 HCl + 40 H2O 3.18g
Time (seconds) Volume of gas (cm³)
20 4
40 6
60 8
80 11
100 13
120 14
140 16
160 18
180 20
200 22
220 25
240 27
260 30
280 33
300 37
To ensure accuracy in my method I have an effective experiment would be to twist the gas syringe back and forth so as to not get the syringe stuck, which could affect our results. Another thing would be to sieve the chips so to get the best marbles we can.
Averages were taken down for all my results and these were:
50cm³ hydrochloric acid and 0cm³ water =
25 50 78 100 20 48 74 100
40cm³ hydrochloric acid and 10cm³ water =
15 33 54 75 95 100 12 27 45 63 82 99 100
30cm³ hydrochloric acid and 20cm³ water =
9 19 33 50 67 82 98 100 10 20 36 55 68 76 84 96 100
20cm³ hydrochloric acid and 30cm³ water =
8 16 26 34 54 68 82 94 100 8 16 28 32 58 66 83 94 100
10cm³ hydrochloric acid and 40cm³ water =
4 7 8 9 10 11 12 13 14 16 18 20 22 24 26 28 4 6 8 11 13 14 16 20 22 25 27 30 33 37
Skill Area A
Analysing Evidence and drawing Conclusions.
Trial Experiment 1, 50cm³ hydrochloric acid and 0cm³ water.
Trial Experiment 2, 40cm³ hydrochloric acid and 10cm³ water.
Experiment 3, 50cm³ hydrochloric acid and 0cm³ water.
Experiment 4, 40cm³ hydrochloric acid and 10cm³ water.
Etc.
As you increase the concentration of the hydrochloric acid the rate of the reaction increases. We can say this by looking on all of the graphs above- the steeper the line is on the graph; the faster the reaction is taking place. The 50cm³ hydrochloric acid and 0cm³ water graph has the steepest line because it is the most concentrated acid.
Therefore, the other graphs with different concentrations are not as quick to react to reacting with the calcium carbonate chips as the experiment is when adding 50cm³ hydrochloric acid and 0cm³ water to the marble chips.
Skill Area E
Evaluating Evidence
In all fair honesty I do believe that my experiment went very efficiently with a few set backs which I will go into detail later. From looking at my results I can see that there were no anomalous results, which was a good thing, and it proves that everything went very well. Even though the experiments went very well I decided to repeat the experiments and I got roughly the same results, which is what I did do, and these to went very well.
The sources of errors which ended up altering the final results were as a possibility the temperature of the acid, and whether or not it had changed from when we did the first reading to the finish i.e. from when we did the first experiment.
From looking at my results and graph I am able to conclude that the more concentrated the acid the quicker the reaction happened and the more gas was produced. As we look at the graphs we can clearly see that in all five results at the beginning the reaction happened more quickly than at the end where we can see that it started to tail off.
Before I did the experiments I made some predictions - I predicted that the higher the concentration, the faster the reaction will take place and therefore more carbon dioxide will be produced- this was completely correct as you can see from the graphs. Also I came to the conclusion from looking at my predictions that the smaller the stones are, the even quicker the reaction will happen; this is because the acid has a larger surface area to act upon, and I believe that all my predictions were right.
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 that 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.
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 0.01g this would account for a slight margin of error. The liquid measurements were accurate to 1cm³ because this was how the cylinders were marked.
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.
My results seem to indicate a clear pattern from which I was able to confidently draw a conclusion. This conclusion confirmed my hypothesises
The reaction released thermal energy. I can say that no other energy was deliberately put in or taken out of the contents of the conical flask during the experiment. I used roughly the same weight and three chips of roughly the same size throughout the whole experiment, this kept the surface area constant, but something unexpected happened. The truth of my conclusion is not undermined by this however, as the same effect happened to each test. I could overcome this problem in three ways to obtain more accurate results by using a water bath in the experiment to keep the temperature the same throughout the whole experiment, for the first. Secondly, to keep the surface area the same of the marble chips I could grind the chips to a powder to know that the surface area was the same. And third and finally, I could set up my apparatus so that I don’t have to drop the calcium carbonate chips into the conical flask but instead put the amount of hydrochloric acid and water into the flask and then attach a small test tube on a piece of string between the inside of the flask and the bung and shake the flask successfully allowing the chips to drop into the bottom of the flask without any carbon dioxide lost.
I could have repeated the experiment a lot more times to get a more accurate average or I could have used a larger gas syringe to obtain more readings in a longer space of time. Using different acids would have been interesting if I wanted to make any improvements/ further investigations and looking at more concentrated acids and how they react to calcium carbonate and whether all the acids had the same results. Also, I could measure the mass loss of the reaction by having the conical flask on a top pan balance. I could take away the mass at regular intervals from the original and find out how quickly the reaction takes place.