How temperature affects the rate of reaction between Marble and Hydrochloric acid
Introduction
This experiment will show how temperature affects the rate of reaction between marble and hydrochloric acid. CaCO3 + 2HCL =
The results could be measured in several ways, one would be to time until the limestone has dissolved or the other method would be the measure the amount of air lost every x seconds, I will choose the latter because it is a more accurate way of measuring the rate of reaction.
In our preliminary we tested out various sizes of marble chips and various amounts of hydrochloric acid to make our actual experiment come up with very accurate results.
Prediction
The variable we have chosen to investigate is temperature. Collision theory states that when a particle is given energy it vibrates and the more energy it is given the more it moves and so the more collisions there are the higher the chance of a successful collision is which raises the rate of reaction. I predict that as the temperature goes up so the rate of reaction will increase with it. It is also safe to predict that if I double the temperature the rate of reaction will roughly double. The energy given to the particles of hydrochloric acid and limestone will also make it reach the activation energy needed quicker increasing the rate of reaction as well. The illustration shows the activation energy marked with a pale yellow arrow. It is the difference between the energy of the activated complex at the top of the hill and the energy of reactants.
Collision theory
However, not all collisions in a reacting mixture result in a reaction. The particles (molecules or ions) in the mixture will have a whole range of different energies. Some have lots of energy and move about quickly; others have a low energy and move more slowly.
In order for the collision to produce a reaction, the particles must have enough energy to allow the reaction to take place. This minimum amount of energy is called the activation energy of the reaction.
(particles must have sufficient energy to react together)
The particles with insufficient energy just collide with each other without reacting.
Preliminary Practical Work
I conducted some preliminary practical work to test whether my background research is correct. I will look at the reaction between Calcium Carbonate and Hydrochloric acid, and see whether the factors that I have researched do actually affect ...
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In order for the collision to produce a reaction, the particles must have enough energy to allow the reaction to take place. This minimum amount of energy is called the activation energy of the reaction.
(particles must have sufficient energy to react together)
The particles with insufficient energy just collide with each other without reacting.
Preliminary Practical Work
I conducted some preliminary practical work to test whether my background research is correct. I will look at the reaction between Calcium Carbonate and Hydrochloric acid, and see whether the factors that I have researched do actually affect reaction rate. I will test temperature, particle size and concentration. I am looking at the amount of fizzing produced when calcium carbonate and hydrochloric acid react to become calcium chloride, carbon dioxide and water.
Calcium carbonate + hydrochloric acid Calcium chloride + carbon dioxide + water
CaCO3 + 2HCl CaCl2 + CO2 + H2O
The amount of fizzing does not need to be measured very accurately because these preliminary experiments are qualitative experiments, not quantitative, just to show that the factors which I have researched do actually have some affect on reaction rate in the way in which I expect them to. I will just record which sample from each experiment is the fastest and which is the slowest from observation, times or other detailed results are not necessary.
Temperature
I will put pieces of similarly sized calcium carbonate into beakers of hydrochloric acid of the same concentration, but different temperatures, and record the rate of reaction in comparison to the other samples.
10ml acid and 10ml hot water 10ml acid and 10ml cold water
10ml acid, 5ml hot water and 5ml cold water
Results:
Concentration
I will put pieces of similarly sized calcium carbonate into beakers of hydrochloric acid of different concentration, but with the same temperature. I will record the reaction rate in comparison to the other samples.
10ml acid 5ml acid, 5ml water 2ml acid, 8ml water
Results:
Particle Size
I will put pieces of calcium carbonate of various sizes into beakers containing 10ml of hydrochloric acid, which are the same concentration and the same temperature. I will record the reaction rate in comparison to the other samples.
Large calcium carbonate crystal Small calcium carbonate crystals calcium carbonate powder
Results:
Conclusion
My background research is correct. Surface area, temperature and concentration do affect reaction rate, in the way in which I expected. This means I can now use one of these variables in the main investigation.
Sodium Thiosulphate and Hydrochloric Acid
I will now look at the reaction between sodium thiosulphate and hydrochloric acid. I will be using this reaction for the main investigation, looking at how concentration affects this reaction rate. I am going to test this reaction to check that something does happen, what if anything does happen, and to find out how I can measure the main investigation.
I will put sodium thiosulphate and hydrochloric acid into a conical flask with a cross underneath. I expect the cross to disappear as the reaction takes place.
It took 17.2 seconds for the cross underneath the flask to disappear. It disappeared because the solution went a cloudy yellow colour. It also gave off a smelly gas. This proves that a reaction does occur between sodium thiosulphate and hydrochloric, and I can measure the rate of it by timing how long it takes to go cloudy. I can use this reaction to test the affect concentration has on reaction rates.
Effect of Concentration on Sodium thiosulphate and Hydrochloric acid
The equation for the reaction between sodium thiosulphate and hydrochloric acid is:
Sodium thiosulphate + hydrochloric acid sodium chloride + sulphur dioxide + sulphur + water
Na2S2O3(aq) + 2HCl(aq) 2NaCl(aq) + SO2(g) + S(s) + H2O(l)
From this I can see that the cloudiness of the water is due to the formation of sulphur. Unlike the other products of this reaction sulphur is a solid, and it is the particles of this solid which are present in the water making it turn cloudy. So in actual fact when measuring this reaction I am measuring the rate of formation of sulphur.
Prediction
In the main part of my experiment I am going to test how concentration will alter the rate of the reaction between sodium thiosulphate and hydrochloric acid.
I think that if either or both of the solutions is less concentrated the reaction rate will be slower. This is because there are fewer particles in the same volume of the solution, so they will collide less. This means it will take longer for the particles to gain enough energy for a reaction to occur, it will take longer for the particles to overcome the activation energy barrier so there will be fewer reactions.
I think that reducing the concentration of sodium thiosulphate will have more effect on the reaction rate than reducing the concentration of hydrochloric acid. This is because the sodium thiosulphate is the compound that contains sulphur. Since we are measuring the rate of formation of sulphur, if there is less sulphur it will take longer for the solution to turn cloudy, making the reaction rate slower.
Although changing the concentration of hydrochloric acid will affect the rate of reaction, it will not have as much affect as the sodium thiosulphate because there will still be the same amount of sulphur present.
Plan
Fair Test
During the whole of this investigation I will make tests fair by keeping everything apart from one variable exactly the same. This includes:
- Using the same size and shape of flask each time, so the timing for when the cross disappears can be measured more accurately and fairly.
- Trying to keep the room temperature the same so temperature doesn’t affect my results.
- The same person doing all of the timing, because their reactions for when the cross disappears should be constant.
- Using the same overall volume of liquid in each test.
- Using separate measuring cylinders for each solution, sodium thiosulphate, hydrochloric acid and water, so they do not contaminate each other.
Analysis of Results
From my results, I notice that there is a considerable difference in the time for the cross to disappear from the lower temperatures to the higher temperatures. All of the times are pretty much the same for the two recordings indicating that the experiment was a pretty successful one. There were no anomaly. The average time taken for the reaction descends, as the temperature gets higher- There is a decrease of almost 163 seconds from the starting temperature to the finishing one.
The results clearly show that the time for the cross to disappear decreases as the temperature increases.
In my experiment I found that during the reaction between Hydrochloric acid and Sodium Thiosulphate, when the Hydrochloric acid is added to sodium Thiosulphate solution, a fine deposit of sulphur is formed. The sulphur makes the solution cloudy. As more and more sulphur is formed, the solution becomes more and more cloudy. Soon it becomes impossible to see through the solution.
From my results, I have come to the conclusion that if the temperature of a solution is raised, so is the time for the reaction to occur. The cross disappeared more rapidly as the temperature rose and I think this was due to the increase of energy between the particles and an increase in energy between collisions that successfully passed the energy barrier. This produced the sulphur at an increased rate, which turned the solution cloudy thus making the cross invisible.
At the lower temperatures, the time for the cross to disappear was greater because the particles did not have as much energy as they did at the higher temperatures. At high temperatures the particles are colliding with much more energy and thus the reaction that releases sulphur works and now releases more sulphur at a much quicker rate thus increasing the rate at which the cross disappears.
From the graph it can be seen that at the highest temperatures there is a greater increase in rate. So from;
20-30oC rate increase 0.008s-1
30-20oC rate increase 0.007 s-1
40-50oC rate increase 0.006 s-1
50-60oC rate increase 0.030 s-1
60-70oC rate increase 0.032 s-1
The first three have an average difference of 0.007 s-1 yet the last two have an average difference of 0.030 s-1.
My original prediction was that if you increase the temperature of a reaction, you decrease the time it takes to occur. And, from looking back on my results, I can see that this hypothesis was correct as the time for the cross to disappear decreased as the temperature rose. My conclusion matches my prediction very well overall, and my results clearly show this where at room temperature, the time for the cross to disappear was 274 seconds and at 70oC the time for the cross to disappear was 11 seconds - a difference of about 263 seconds. Thus when Hydrochloric acid was reacted with Sodium Thiosulphate the particles in the solution were moving around with more energy; enough to break the energy barrier and for a reaction to occur as the temperature rose.
Evaluation
I think that this experiment has gone very well. My results were of a particularly accurate standard as I did each temperature the reaction was taking place twice and calculated an average from these times. There were no strange results (anomalies) within my results table although I didn’t get the exact results I expected. I found that during the last two temperatures the rate was much increased.
Reliability of results can only be shown by repeating the experiment a number of times. I could have therefore improved upon the reliability of my experiment by repeating the experiment 10 times. The reason this was not done initially was due to time considerations that are imposed in a classroom situation.
Accuracy of my results was dependant upon my observations so I may have introduced an error into the results. This is because my judgement of the cross disappearing may differ to another students, so were they to repeat my practical they may not obtain results which tally with mine. This however does not effect the overall analysis of my practical as I alone judged when the cross had disappeared therefore negating the error. In order to obtain results which are of a more accurate nature I could have used a light meter to judge the intentsity of the precipitate formed.
I believe that I did get a suitable range of results for this experiment. I recorded results from temperatures that ranged from Room Temperature to 70oC and I think that this is a very good range to see how temperature affects the rate of reaction. However, I feel that this also reduces the chance of knowing if anything changes if the temperature reaches a certain point. Perhaps raising the temperature even higher would have produced a different set of results which may mean that a limit may exist for the rate of the reaction.
Some other areas in the experiment that I feel I could have improved on were factors like controlling the stopwatch and measuring the amount of Sodium Thiosulphate and hydrochloric acid. There is lots of room for human error here. For example I could have used a burette for measuring the HCL or Thiosulphate rather than using a measuring cylinder. However the inaccuracies due to them were negligible because I paid close attention to these during the experiment. I did outline in my plan that I was going to heat the Sodium Thiosulphate using a water bath, however, this option was not available to me due to the lack of time and resources, I ended up heating the Thiosulphate in a flask sitting on a gauze mat.