To know how fast a reaction is going to be you need to know the rate of each reaction. Rate is a measure of how fast or slow something is.
On graphs – the concentrations with the steepest gradient will have the fastest rate of reaction.
Apparatus
- A boiling tube.
- Rubber bung – to put on boiling tube to stop CO gas produced, from escaping.
- A gas syringe.
- A measuring cylinder.
- A delivery tube (for connection to the gas syringe.)
- A clamp stand.
- A stopwatch.
- Calcium carbonate marble chips. (CaCO )
- Hydrochloric acid of different Molars. (HCl )
Safety
I will wear safety goggles due to the fact that I am handling acid. I will also wear a lab coat to prevent spillage of acid on my clothes. By chance, if any acid comes into contact with my skin, I am aware that I must wash it off with
Factors to be kept constant
- I will try to make sure that the marble chips will be about the same size, this is because I want to keep the chips as similar as possible throughout the experiment due to surface area, and hopefully be a fair test with the results in direct relationship to each other. If these varied then I would expect the result to be inaccurate.
- I will use the same mass of marble chips throughout the whole of my experiment (3 grams.) I need to keep the Calcium Carbonate at a constant mass, as increasing or decreasing this may alter the rate at which the reaction takes place, this may happen because if there is more or less Calcium Carbonate the powder there is a greater or lesser chance of particle collisions and therefore the ate of reaction would increase or decrease.
- I will make sure I use the same method in the experiments where I intend to produce concentrations between those I have i.e to get 1.5 Mol. I will add 15 cm³ of 1 Mol. and 15 cm³ of 2 Mol. to achieve the concentration in between them both – 1.5 Mol.
- I will use the same volume of acid throughout the whole of my experiment. (30 cm³.)
- I will do all of my experiments at room temperature.
- I will take readings at the same time intervals throughout the whole of the experiment (every ten seconds.)
So that I can say that my results were reasonably accurate and reliable, I must conduct a fair test. I am changing the concentration of Hydrochloric Acid in my experiment so all other variables must be kept the same, if they are not then they may interfere with my experiment. Certain factors will be difficult to keep the same such as the temperature but as long as the experiment is carried out quickly and during one session I do not think it will effect my results to the point of them being anomalous.
Making the investigation reliable
In order to obtain reliable data, I am going to do repeat the experiments for each individual concentration 3 times. I am doing this, as it will allow me to calculate an average of the three readings, giving me a more accurate result, and later if I need to repeat any experiments I can. An important point is that I must use the right amount of acid and the best-sized amount of marbles. I also need to be accurate when measuring out concentrations especially when measuring out 1.5 and 2.5 as to achieve them concentrations I need to add two concentrations together, making sure I add the exact same amount of each.
Plan
When doing my experiments I will use the same procedure throughout. I will set out my equipment as shown in the Apparatus section. Throughout the experiment I will be ready with the stopwatch, so that I start and stop it immediately as it is necessary to get accurate readings. Once I have set up the apparatus I will measure out 30 cm³ of acid in a measuring cylinder and then pour it into the conical flask. I will then accurately weigh out 3 grams of Calcium Carbonate chips using a top pan balance. I will then quickly place the chips into the acid, insert the bung in the top of the boiling tube and start the stopwatch. This must be done in as short a space of time as possible. From then on, I must take the reading of the volume in the gas syringe every ten seconds, to give me enough results to produce a reasonable sized graph. Overall, I will use five different Molars of hydrochloric acid:
- 1.0 Molar
- 1.5 Molar
- 2.0 Molar
- 2.5 Molar
- 3.0 Molar
The only concentrations available to use are:
- 1.0 Molar
- 2.0 Molar
- 3.0 Molar
(I will have to produce the 1.5 Molar and 2.5 Molar myself:
- I will need to add 15 cm³ of 1.0 Molar and 15 cm³ of 2.0 Molar to help me to achieve the middle concentration (1.5 Molar.)
- I will need to add 15 cm³ of 2.0 Molar and 15 cm³ of 3.0 Molar to help me to achieve the middle concentration (2.5 Molar.))
I will then record the amount of carbon dioxide in the gas syringe. I will take into consideration that the speed with which I put in the marble chips, place in the bung and press the stop watch may well affect how well the experiment works. Although these factors will affect the end result so long as they are kept constant throughout then it should not matter too much.
Conclusion
Looking at my graphs, I can see that I didn’t have any major anomalous results, which show my results were reasonably accurate.
“I predict that as the concentration of hydrochloric acid is increased the faster the rate of reaction will be.”
“On graphs – the concentrations with the steepest gradient will have the fastest rate of reaction.”
This is a prediction I made before the experiment. It was proven to be correct, because from looking at my graphs, I can see that the highest concentration I used (3.0 Mol.) has the steepest gradient on the graph, proving the rate of the reaction to be the fastest.
This is because: “A reaction occurs when particles collide with each other. The more concentrated a solution is the more particles there are. The particles will gain more energy because the frequency of collisions will increase. Therefore, if the frequency of collisions is increased, the rate of reaction will be increased. The result of the experiment if the theory is accurate means the collisions between the particles of hydrochloric acid and Calcium Carbonate should occur faster, this means the time taken for the reaction to occur should be faster. The less concentrated the solution the fewer particles there are; the result of this should be the opposite of the more concentrated solution.”
Evaluation
From looking at my graphs, I can see that I had no major sources of error, as the majority of my results fit onto my line of best fit, showing that my results were reasonably accurate. However, there were numerous sources of error that I had no control over, despite my results not being greatly affected by them:
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It was difficult to be sure I am mixing the exact amount of acid when mixing two different concentrations together to achieve the concentration between the two being mixed.
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I could have overcome this problem by taking more care when measuring out the concentrations, to ensure I get the exact amount of each.
- It was difficult to be sure I was achieving exactly 30cm³ of hydrochloric acid every time.
- I could have overcome this problem by taking more time and care when measuring out the volume of the acid.
- It was difficult to measure out exactly 3 grams of calcium carbonate chips in all of my experiments.
- I could have overcome this problem, by taking more time and care when measuring out the calcium carbonate marble chips.
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I was unable to press the stopwatch at the exact same time when the acid and marble chips came into contact with each other (beginning of reaction), and I was unable to apply the bung straight away.
- I could have overcome this problem, by allowing a small time interval that was equal for each of the experiments, allowing me time to apply the bung and start the stopwatch, so that all my experiments would have been fair.
- Most of the marble chips were of different shapes and sizes – therefore, the marble chips would have not had the same surface area, making my results slightly inaccurate.
- I could have overcome this problem by using marble chips of similar shapes and sizes, or to be even more accurate, I could ensure that all marble chips have the same surface area, by taking more time to measure them.
- The gas syringe may have got slightly stuck, when Carbon Dioxide
(CO ) gas was being produced.
- I could have overcome this problem by twisting the gas syringe back and forth before each experiment in hope that the syringe would not get stuck during the experiment, which would affect my results.
I think that the procedure I used for my experiment worked quite well. There are no major ways I think I could have improved my experiment as I did not get any major anomolous results, however, if I were to repeat the experiment, I could take more time and care to eliminate sources of error, in order to help me achieve better results.
I think that I received enough data to be sure about my conclusion, and also I think that the range of concentrations I finally decided to use in my final experiment were a good range of concentrations. This is because, the results I achieved, produced a reasonably good shaped graph. I do not think that I need to take more readings in between those I have already taken, but if I were to repeat the experiment again, I would use concentrations in between those already used to give me a more accurate outcome.