Surface Area – The surface area would normally affect the rate of reaction but because we are using two solutions this factor will have no affect on the rate. In a solid though the bigger the surface area the faster the rate of reaction. This is because when the surface area is larger there are more surfaces for the particles to react with. Breaking it up into smaller pieces increases the surface area of a solid.
Pressure – Increasing the pressure is similar to increasing the concentration. The particles will collide more frequently at a higher pressure and increase the rate of reaction. The pressure though only has a big effect on gases and not liquids, which is why it will not be a major factor to control.
Fair Test:
Many things will be done to ensure that our experiment is a fair test because there are a lot of factors that can affect the rate of reaction as talked about above. For example, surface area and temperature affects the rate. The way in which we will control these factors is to keep them constant.
There are also many variables that will be measured and kept the same or changed. By breaking them down it is easier for us to follow:
Independent Variable: Concentration of the acid (2HCl)(mol)(controlled for preliminary exp.)
Dependent Variable: The volume of CO2 emitted (ml/cm³)
Controlled Variables (What I need to do/control to make it a fair test):
• The temperature of the room where the reaction is to take place
• The volume of hydrochloric acid
• The mass of calcium carbonate (not for preliminary exp.)
• The equipment that was used:
-I need to make sure the movement of the gas syringe is smooth to get optimum
Results
-The conical flask has to be thoroughly cleaned after each test so no remains of
the past substance is left behind with the chance of affecting the following
results obtained
-Make sure to keep the angle of which the gas syringe was positioned at the
beginning the same throughout all the experiments. So as to keep the force that
the syringe has to exert as CO2 enters to get to a certain distance the same.
Materials:
• 25 ml Hydrochloric acid (2 mol, varies in main results)
• Calcium carbonate: -small/powdered marble chippings (1g, 3g, 5g)/
-medium marble chippings (1g, 3g, 5g) /(Just 2g in main results/controlled)
-large marble chippings (1g, 3g, 5g) /
• 1 x gas syringe and conical flask
• 1 x 100ml measuring cylinder
• 1 x rubber tube and bung
• Electric balance
• Stopwatch
• Metal stand and claw to hold the gas syringe
Safety:
Whilst doing our experiment we have to take into account the various safety measures to abide by. For example a bench mat is needed to ensure that the desk doesn’t get burnt and also safety goggles need to be worn at all times for protection over the eyes. This is because the chemicals that are going to be used are irritants and also the reaction produces other irritant chemicals and one of the gases given off is toxic, though it is given off in small quantities and is therefore relatively harmless. If any acid spills on you, you must wash your skin immediately. We also need to ensure there is safe working space for us to work in.
Things I will do to keep safe are: Wearing goggles; standing up in case I spill the hydrochloric acid; tucking my chair in so I don’t trip over; being careful with the hydrochloric aid; check my equipment has no blockages, as the conical flask will blow up if the pressure of carbon dioxide gets too high; clear up the hydrochloric acid straight away if I spill it, as it is corrosive and someone may put their hand in.
(Created using ‘Paint’)
Method: Preliminary (Note: All measurements of volumes were taken at eye level)
1. 25ml of hydrochloric acid (2mol) was poured and measured into a measuring cylinder and then poured into a conical flask.
2. 1g of calcium carbonate large marble chippings was placed on a clean sheet of paper and weighed out with an electric balance.
3. The calcium carbonate was carefully and quickly placed into the conical flask and the timing began straight after the lid was placed on with the assistance of a stopwatch.
4. With the gas syringe and the timer being constantly monitored; the volume of CO2 emitted was recorded at intervals of every 10 seconds.
5. After 100 seconds, the mixture from the flask was emptied, and the gas syringe and conical flask were rinsed with distilled water and dried.
6. The experiment was repeated from Step 1-5, instead of using 1g of marble chippings it was replaced with 3g.
7. The experiment was again repeated from Step 1-5, with 5g of marble large chippings.
8. We then repeated steps 1-7 using medium sized chippings and small/powdered chippings.
Results of preliminary experiment:
Large pieces of marble chippings, 2 mol HCl
Medium pieces of marble chippings, 2 mol HCl
Small/Powdered pieces of marble chippings, 2 mol HCl
The observation that I have witnessed is that when the calcium carbonate was added to the solution of hydrochloric acid there was a high intensity of fizzing which released carbon dioxide gas. With time, the fizzing became less intense and which meant that one or more of the reactants has been used up in the reaction. At higher surface areas of marble chippings the intensity of the fizzing increased and CO2 was emitted faster, which meant that an increase in surface area caused a faster rate of reaction.
(Graph)
Discussion
My charts show that the higher the concentration of hydrochloric acid, the higher the volume of carbon dioxide in a certain time. This is because as the concentration increases, the number of acid particles in the same volume increases, therefore there are more reactant particles and there is more of a chance of a reaction taking place since there are more collisions.
The preliminary results have given me decisive evidence as to what I should use for my main experiment. We feel that taking the results every ten seconds is the most appropriate, any shorter and chances of missing one and then going over the other will be too high. Any longer and results won’t be accurate enough, one wrong record could mean a significant disparity the results that should have been obtained.
Secondly, by looking at how long each mass and surface area took to surpass 100ml/cm³, it has allowed me to settle on using 2g of large sized marble chippings. I’ve been able to accurately choose because 2mol is one of the more concentrated of the acid I will be using, and therefore any that increase too quickly here I know for sure will be even faster and harder to obtain results from with 3mol. The small/powdered chippings exceeded 100ml/cm³ even at just 1g and so were crossed out straight away. Also because they were so small a pieces, it wasn’t a simple task getting it all into the conical flask. If a small amount got misplaced, it would be impossible to regain it and we cannot afford to waste time going through all the weighing again. Even if a tiny fraction of it fell it is likely to show on our results, causing them to lose their validation and value.
Although medium sized chipping were certainly a lot easier to handle and gain valid results from than small ones, large were by far the most reliable and accurate of all the sizes. By choosing large, we are using a dependable control for the surface area. By keeping the surface area to a minimum it has allowed us to focus on choosing an ideal mass. Looking at the table it is palpable that 2g is the most convenient. The CO2 emitted by 5g is too rapid for us to gain any serviceable records, passing 100ml/cm³ after just 30 seconds. There was the same problem with 3g, if maybe not as unusable as 5g. With 1g there was notable distance from the 100ml/cm³ after 100 seconds that it was straightforward to go with 2g which is in between both values that were of the two extremes.
I have also decided to take down results until either it the volume passes the 100ml/cm³ mark or once 5 minutes has passed (300 seconds).
For the purposes of rate equations and orders of reaction, the rate of a reaction is measured in terms of how fast the concentration of one of the reactants is falling. Its units are mol dm-3 s-1. However, for object of this experiment, it will has little or no relevance as we are not measuring the difference in concentration before and after the reaction but instead basing it on the measurements of one of the products produced, in this case its CO2.
Method: (Note: all measurements of volumes were taken at eye level)
1. Firstly I will collect all of my equipment and set it up, like in the diagram.
2. I will measure the mass of my marble chips to 2g, and measure the volume of Hydrochloric Acid to 25cm of the correct concentration.
3.I will then add my marble chips to the Hydrochloric Acid in the conical flask; then quickly start the stop clock and put the bung in the conical flask, without letting any Carbon Dioxide escape.
4. I will take down the volume of Carbon Dioxide every 10 seconds and record it in my table.
5. I will find the rate of reaction by choosing two points on my line or tangent then applying this formula: Change in x axis
Change in y axis
6. I will repeat steps 1-5 three times for each concentration: 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0 mol ( the results of the 0.5, 2.5 and 3.0 were achieved by teaming up with other group from a different class), and if there are any results that don’t follow the pattern I will repeat them. Also if there are any anomalies I will repeat the experiments, that is of course if there is time.
Note: temperature affects the frequency of collisions. An increase in temperature will increase the average kinetic energy of the reactant particles and therefore increases the frequency of collisions which results in an increasing in reaction rate. A decrease in temperature will have an oppose effect. This is why I will bring a thermometer to measure the temperature before and after each reaction, so as to be as accurate as possible with the judgement as to how reliable the results are.
Also, I have chosen to record all my results to one decimal place. This is because it will make my overall result a lot more accurate and detailed. However, due to the fact that the gas syringe does not mark the decimals, I will record them to the nearest half. It will make it more precise, and at the same time I will not be simply guessing as to what value they may be.
Results:
Concentration of HCl: 0.5 mol
Temperature before = 21°C Temperature after = 21°C
Concentration of Hydrochloric Acid: 1.0 moles
Temperature before = 21°C Temperature after = 24°C
Concentration of Hydrochloric Acid: 1.5 moles
Temperature before = 22°C Temperature after = 22°C
Concentration of Hydrochloric Acid: 2.0 moles
Temperature before = 22°C Temperature after = 22°C
These are the original results for 2.5m and 3.0m concentrations taken by our other team in the first practical, however when I came to plot the averages on my graph, the pattern didn’t fit and there was a lot of error. Luckily for our group, we had plenty of time after our share of recording so we repeated the experiments and got better results.
Concentration of Hydrochloric Acid: 2.5 moles
Temperature before = 21°C Temperature after = 21°C
Concentration of Hydrochloric Acid: 3.0 moles
Temperature before = 21°C Temperature after = 21°C
The results below are those that I repeated for the 2.5m and 3.0m concentrations:
Concentration of Hydrochloric Acid: 2.5 moles
Temperature before = 21°C Temperature after = 21°C
Concentration of Hydrochloric Acid: 3.0 moles
Temperature before = 21°C Temperature after = 21°C
* Measurements exceeded 100ml/cm3 (noted down as one or two of the other records had still yet to pass it)
Rate of Reaction:
I will find the rate of reaction by taking the fastest reaction time, which is 40 seconds at a 3.0 molar solution. Then I divided the average volume of Carbon Dioxide at 40 seconds by 40. I did this for each of the concentrations. This gives me the average volume (cm³) of Carbon Dioxide produced per second.
When I look at my graph I can see that the rate of reaction for the 1.0m solution is not what I would have expected it to be. However I only found this out once I had done my graph, if I had known sooner I would have repeated the experiments. I think that the rates of reaction are abnormal because whilst I was doing those experiments, the temperature rose from 21°C to 24°C, a rise of 3°C with both the. Therefore I should have repeated the experiments.
Also, looking at the rates of reaction below, I can see that the rate of reaction were slightly high for concentrations 1.5 and 2.0m this may have resulted from the fact that the temperature was 1°C higher than the rest. My theory as how this may have occurred is that it was the conical flask that had heated up when doing tests for 1.0m, and was still cooling whilst recording the other two. As for the cause of the rise in temperature in the first place, we are still searching for an answer.
0.5m solution: 1 ÷ 40 = 0.0250 cm³/ second
1.0m solution: 6.8 ÷ 40 = 0.1700 cm³/ second
1.5m solution: 26.8 ÷ 40 = 0.6700 cm³/ second
2.0m solution: 33.8 ÷ 40 = 0.8450 cm³/ second
2.5m solution: 35.7 ÷ 40 = 0.8925 cm³/ second
3.0m solution: 82.5 ÷ 40 = 2.0625 cm³/ second
Gradient:
I will find the gradients of the straight lines on my graphs by picking two points along the line and dividing the difference in the x axis by the difference in the y axis. For the curved lines I will draw a tangent and pick two points on that line and then divide the difference in the x axis by the difference in the y axis. This also gives me the volume (cm³) of Carbon Dioxide produced per second, but with this I can work out the time or volume of carbon dioxide for experiments that I didn’t do. This gives me a specific volume of Carbon Dioxide produced between the two points that I used to work out the gradient, whereas the rate of reaction gives me an average rate of reaction.
0.5m solution: 9.5 ÷ 50 = 0.19 cm³/ second
1.0m solution: 16.5 ÷ 50 = 0.33 cm³/ second
1.5m solution: 39.0 ÷ 50 = 0.78 cm³/ second
2.0m solution: 48 ÷ 50 = 0.96 cm³/ second
2.5m solution: 52 ÷ 50 = 1.04 cm³/ second
3.0m solution: 40 ÷ 20 = 2.00 cm³/ second
The graphs do show a general trend. With an increase in concentration in each solution (calcium carbonate and hydrochloric acid), there was an increase in speed of CO2 emitted (increases the rate of reaction). The results that were obtained did support when comparing to the hypothesis. An increase in the concentration of the solution increases the reaction rate also.
This is explained using the collision theory. Changing the concentration in which the reaction takes place effects how rapidly the amount of product is produced i.e. the reaction rate. A decrease in concentration will reduce the amount of hydrochloric particles in a certain volume which leads to less number of reactant particles in a particular time that would have collided with at least activation energy. There is a similar occurrence when changing the surface area of marble chippings that is exposed to the acid, the less calcium chloride exposed, the less chance of a hydrochloric particle colliding into one, therefore decreasing rate of reaction. With no activation energy, not many particles will react to form products i.e. lowers the reaction rate because it took longer for the particles to collide with one another, let alone one with enough energy. A higher concentration increases the number of the reactant particles in a certain volume which is equal or greater than activation energy at a particular time which leads to more product being formed more quickly i.e. increases the reaction rate.
I have found the rate of reaction using my results; this also shows that my prediction was correct as the rates increase as the concentrations increase. I cannot see any other relationships between the variables, other than as one increases the other increases, such as direct proportion.
My results and my graph both show that my prediction was correct; that as the concentration of Hydrochloric Acid increases, the volume of Carbon Dioxide increases.
Evaluation:
The method that we used to collect the results was effective and appropriate for the investigation. However we could have improved our method by using the same size calcium carbonate/marble chips, as it was difficult to find those that were of the same size, even though they were already categorized to three different ones. It was never a straight forward task being able to accurately control the surface area and therefore may have affected the experiment. Also, it was quite hard to put the marble chips into the hydrochloric acid, then start the stop clock and put the bung into the top of the conical flask all at the same time, this may have affected the experiment as we may have let some carbon dioxide escape or we could have started the stop clock too late and then the timing would be wrong.
Another shortcoming was the fact that we only had equipment that measured to 100 cm³. It would have made our results more accurate if we had used equipment that measured to 200 cm³. Also, to make the investigation more accurate we could have tested more concentrations of hydrochloric acid to see if they followed the pattern and to help us work out the relationship between the two variables. If we had tested the concentrations in between our concentrations it would have made the investigation more accurate and would have shown a much clearer relationship.
I think the results are reliable because the maximum variation is 4.5 cm³ at 120 seconds for the 1.5m solution and 4cm³ at 30 seconds for the 2.0m solution. Most of my variation is below 10% but there are quite a few that have a higher variation, I think that I have variation because I couldn’t use exactly the same sized marble chips for every experiment. There is some error in my results but I only have a few anomalies, which I think may have been down to the size of the marble chips or the temperature may have changed but I didn’t monitor the temperature all through the experiment, only at the start and the end. There are only a few inaccuracies. I think that the inaccuracies are because the temperature rose by 3°C at 1.0m and the1.5m and 2.0m were 1°C higher than what the other ones were. Using a water bath would ensure a constant temperature. Therefore we will not have to worry about keeping it controlled and this would make collecting the results easier. However, it could also be because that all of the marble chips differ in size during those experiments, there was a lot of change in them.
The improvements to help reduce errors and to improve accuracy, the experiment could have been repeated multiple times at same temperatures and/or repeated at different temperatures. Also, the experiment could have been conducted using a different concentration to determine if a change in temperature has the same effect on reaction rate. The volumes and temperatures of the solution could have been measured using more accurate equipment, with a smaller scale which will be easier to record.
In terms of expanding on what we’ve already done, we could have taken the investigation further by changing the volume of hydrochloric acid to see what affect that has on the rate of reaction. We could have also changed the mass of calcium carbonate used to see whether changing the amount of reactant changes the rate of reaction.
The systematic errors in this experiment were:
• Incorrect calibrated electronic balance, thermometer, gas syringe and stopwatch which can cause the recordings that are different to the right value.
• The impure or contaminated HCl and CaCO3 could have been present which are different to the supposed value.
The random errors in the experiment were:
• The inconsistency or recording certain temperatures and weights at certain time intervals with the stopwatch
• Inability to predict if all the CaCO3 is added to the conical flask
• Inability to predict when to start the timing of the reaction
• Parallax error of reading the thermometer and gas syringe at eye level
• Escaping gases while placing the CaCO3 in the reaction starts before adding the bung
• The inability to maintain the reacting solutions at constant temperature. Even the smallest change in the temperature will have a major effect to the reaction rate.
Bibliography:
• Chemistry for You – Lawrie Ryan (1996),Stanley Thornes publishers ltd., Cheltenham
• Chemistry – Hunt and Sykes
• Nuffield A level Chemistry
• AS Chemistry – A. Hunt
• GCSE Science Revision – K. Hirst
