- Change in mass – Measuring the speed of a reaction that produces a gas can be carried out on a measuring scale/mass balance. As the gas is released the mass disappearing is easily measured on the balance; the quicker the reading on the balance decreases, the faster the reaction happens.
- Downward displacement of water – This simply refers to the collection of gas using water. In this instance carbon dioxide is collected when it is given out from the reaction over time and is collected by an upside-down measuring cylinder filled with water, submerged under water so the gas rises to the top of the cylinder.
- Use of gas syringe – This involves the use of a gas syringe to measure the volume of gas given off. The more gas given off during a given time interval, the faster the rate of reaction. A graph of gas volume against time elapsed could be plotted to give a rate of reaction graph.
I believe that the best technique for this experiment is the use of gas syringe. The reason why I discarded the other methods and chose to use the use of gas syringe is because; the change in mass method is impractical as there is no way to control the rate that the gas is lost, also there is a chance that the batteries may fail on the balancing scale and the experiment will need starting all over again. The downwards displacement of water method is inaccurate as some CO2 may get dissolved in H2O, also the readings on the cylinder is measured up in even numbers, therefore the results are inaccurate, as they have to be rounded to the nearest even number.. However unlike these methods the use of a gas syringe has no faults other than any made by human error; such as not checking the equipment and allowing gas to escape the setup.
Preliminary Tests
Before I started my main experiment I carried out 3 preliminary tests, these test where to find: - what size of marble chip to will be the most suitable – what volume of HCl to use – what range of concentration to use. I need to find these values to use them as constants throughout my main test; this will allow for a fair and precise test and would be suitable for my equipment available. I started off by testing which size chip I was going to use and which one would give me a more suitable value for my equipment, the big small or medium. To do this I would need to know what mass of marble chip is appropriate; obviously HCl is the limiting agent. I have a maximum of 1.0 M of concentration of HCl; this is where the math comes in.
CaCO3 + 2HCl → 1.0 M
Moles = Concentration x volume of HCl = 1 x 20/1000 = 0.02
Moles of HCl = 0.02
Moles of CaCO3 = ½ x 0.02 = 0.01
Mass of CaCO3 = 0.01 x 100 = 1g
From this I was able to conclude that I would need a minimum of 1 gram of CaCO3, therefore I decided to use 1.5 grams of CaCO3 for my main experiment and prelims. Once I found the most suitable weight of CaCO3, I set up my equipment ready for the preliminary.
Method:
1. Weigh out the desired size and weight of marble chips using a measuring scale and put them into a conical flask.
2. Measure out the desired volume of hydrochloric acid that is of a desired concentration using a measuring cylinder.
3. Pour the hydrochloric acid into the conical flask, quickly put on the bung which is attached to the gas syringe and start the stopwatch.
4. After 20 seconds, measure the volume of gas that has been collected in the gas syringe.
5. Repeat the experiment 3 times, to make sure you have reliable results.
Apparatus used:
Gas syringe: Used to measure the volume of gas collected. Check is air-tight before using allowing for reliable results. The gas syringe has a maximum capacity of 100ml.
Electronic measuring scales: Used to weigh the marble chips, more accurate as are electronic and measure to a very small margin.
Measuring cylinder: To measure the amount of acid and water, wash out and dry after each use to allow for more reliable results. There are two types of cylinders that I shall use; a 25ml cylinder for the larger measurements; however I also used a 10ml cylinder for the smaller measurements.
Conical Flask: To perform the experiment in the flask.
Stopwatch: To time the rate of reaction.
Preliminary 1 – What size of Marble Chip.
In this test I used 1.5 grams of all different sizes of chips, small medium and large. I kept the concentration of acid at 1.0 M and used 20 ml of HCl. The results to this test are below:
From this I can conclude that I will use medium sized chips. This is because I want to have a reasonable amount of results, I feel the small chips don’t give enough results and the large chips give too many results and I feel the medium sized chips gave the best amount of results.
Preliminary 2 – What volume of HCl.
In this test I used 1.5 grams of medium sized chips. I kept the concentration of acid at 1.0 M and changed the volume of HCl between 10 ml, 20 ml and, 30 ml. The results to this test are below:
From this I can conclude that I will use 20ml of HCl as this also stopped at 300 seconds and this was ideal as it would have the same values on a graph.
Preliminary 3 – What concentration range is most suitable.
In this test I used 1.5 grams of medium sized chips and 20 ml of HCl. However I changed the concentration between 1.0 M, 0.5 M, and 0.2 M. For this prelim I had to make and use a dilution table, this table would show me what volume of HCl and distilled water I would need to produce the correct concentration of HCl, this is below:
Dilution Table
The results to this test are below:
From this I can conclude that I will use a range from 0.2 M – 1.0 M as it allows for a good range of results however I will use every even decimal ( 0.2, 0.4, 0.6) ect.
Main Experiment
For the main experiment I did 5 experiments and carried out 3 experiments for each of the different experiments and therefore carried out 15 experiments in total for my main investigation. To make my experiment a fair test, I used the concentration of HCl as my only independent variable and the volume of CO2 as the dependent variable that will define the results; I will also be controlling the other variables such as temperature, that I will be keeping at room temperature, about 150C, another variable that I will be controlling is the surface area of the chips, I will be using all medium sized marble chips, another variable that I will be controlling is the volume of HCl, keeping the volume at 20ml, another variable that I will be controlling if the mass of CaCO3, I will be keeping this the same at 1.5g. This will allow for a fair test as all the tests will be the same apart from changing one factor.
Actual Test Results 1.0M
I put this reliable data into a graph so it would be a lot easier to read; I used all the data in this case as there were no anomalous results. I used the data from all three tests to get an average that I used as the main point on my graph; however I also put in error-bars to show how much of a difference there was from the average. I have labeled both axes correctly with correct units, and have a relevant title. My graph is overleaf.
Actual Test Results 0.8M
I put this reliable data into a graph so it would be a lot easier to read; I used all the data in this case as there were no anomalous results. I used the data from all three tests to get an average that I used as the main point on my graph; however I also put in error-bars to show how much of a difference there was from the average. I have labeled both axes correctly with correct units, and have a relevant title. My graph is overleaf.
Actual Test Results 0.6M
I put this reliable data into a graph so it would be a lot easier to read; I used all the data in this case as there were no anomalous results. I used the data from all three tests to get an average that I used as the main point on my graph; however I also put in error-bars to show how much of a difference there was from the average. I have labeled both axes correctly with correct units, and have a relevant title. My graph is overleaf.
Actual Test Results 0.4M
I put this reliable data into a graph so it would be a lot easier to read; I used all the data in this case as there were no anomalous results. I used the data from all three tests to get an average that I used as the main point on my graph; however I also put in error-bars to show how much of a difference there was from the average. I have labeled both axes correctly with correct units, and have a relevant title. My graph is overleaf.
Actual Test Results 0.2M
I put this reliable data into a graph so it would be a lot easier to read; I used all the data in this case as there were no anomalous results. I used the data from all three tests to get an average that I used as the main point on my graph; however I also put in error-bars to show how much of a difference there was from the average. I have labeled both axes correctly with correct units, and have a relevant title. My graph is overleaf.
Evaluation
For the main experiment I did 5 experiments and carried out 3 experiments for each of the different experiments and therefore carried out 15 experiments in total for my main investigation. I feel this is enough information to draw a conclusion; from my graphs I can conclude that there is a resounding amount of evidence that shows that the greater the concentration, the faster the rate of reaction. I believe that my results were very accurate as I took every precaution necessary to allow for the most accurate results possible. All my results clearly fit the trend I described in my conclusion of the graphs, and none presented any anomalous results. While doing one of the 0.6M experiments, the gas syringe tube fell out and we put it back in straight away however a lot of gas had already been lost and the results didn’t follow the trend, so we decided it was best to redo this experiment instead of going with the results we already had. I believe that all my results fit the trend because I was so accurate when carrying out my experiments. I believe that the difference between the repeat experiments are very important as they represent how reliable your results are based on how big the error-bars are, I feel the distance of difference between my repeat experiments is small enough on the whole to show that my results are sufficiently reliable.
How could I improve?
Conclusion
From this experiment I found out that the increase in concentration of HCl the faster the rate the reaction happens, also I have found out that there are other things such as; temperature, catalyst, and surface area all also affect the rate of reaction. My particles collision theory agrees with my data I have collected, this is because the theory suggests that the increase in concentration of HCl will increase the rate of reaction and this is what my research shows. The trends on my graphs show that as the concentration of HCl increase, the rate at which the reaction happens is quicker.