Analysis
In this set of preliminary results we measured the rate of reaction between small marble and 1M of HCl, medium marble and 1M HCl, small marble and 2M HCl. We measured the reaction for 300 seconds and wrote down on the table how far it was at every 20 seconds. From this set of results we learned that the more surface area the marble has the quicker the reaction, and the higher the concentration of the acid the faster the reaction. In this set of results we used the method with the water trough; however we didn't find that it was very accurate so in future we will be using the gas syringes because we feel that it will give us for precise results.
2ND Preliminary Investigation
We did another preliminary experiment to test the efficiency of using the Beehive Shelf method and using a gas syringe. We compared the results together to decide which method we would use in our investigation.
Results
Analysis
From these results we decided to use the gas syringe method, as it was more accurate and there was less room for human error. We also decided that we would extend the time of each individual experiment to 600 seconds, so that the reaction would have time to slow down and so that we could see the full picture of the reaction and not just the first 300 seconds where the initial reaction takes place.
Investigation on the rate of reaction between HCl (Hydrochloric acid) and Marble (Calcium Carbonate – CaCO3)
Aim: In our investigation we have decided that our variable will be the concentration of HCl and to keep the size/surface area of the marble chips (CaCO3) the same throughout the investigation. We are going to time each individual experiment for 10 minutes each (600 seconds) take down their progress every 20 seconds and repeat them 4 times each. We are going to do this because we know from our preliminary results that it is not always a very fast reaction, therefore we need more time for the reaction to be complete and only then will our results be completely accurate. Despite using a water trough in our preliminary work we have decided to use a gas syringe because the syringe was more accurate and reliable.
Equation:
Diagram:
Apparatus
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Gas syringe- to measure the volume of CO2
- 250 ml conical flask- where the reaction takes place
- Delivery tube and bung
- Hydrochloric acid (HCl) 0.25M, 0.5M, 1M, 2M
- Spatula- to measure marble chips
- Digital weighing scales- to weigh out 0.5g of marble chips
- Clamp & stand- to hold glass syringe in place
- Stop clock- to time when we need to write down results (every 20 seconds)
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Measuring cylinder- to measure out 20cm³ of HCl
- Medium marble
- Safety goggles- to protect our eyes
Reason for use of certain apparatus
We used a gas syringe because it was a lot more accurate than the bee hive method that we had used previously; also it was correct to +/-1mm cubed. As well as this we decided to use a digital weighing scale because it is accurate to +/-0.01 grams and the most reliable way to get the right measurement. Also we used a stop clock (correct to +/- 0.01s) so that we could accurately measure the amount of carbon dioxide in the gas syringe. Originally the volume of carbon dioxide (CO2 ) was going to be measured by the beehive shelf method; however we decided to use a gas syringe instead because we felt that it would give us more accurate and reliable results.
Method
- First we set up all of the equipment; connecting the clamp to the stand, fixing the gas syringe into the clamp, attaching a delivery tube and bung to the end of the syringe, and putting the bung into the conical flask. Making sure it was all correct and the same for each experiment we did so that all results were accurate.
- We put the gas syringe into the clamp and then connected the end of the delivery tube to the end of the syringe, it is important that they are properly attached so that no gas can escape during the experiment and the volume of gas will remain accurate.
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Next we measured out the amount of Hydrochloric acid (20cm³) at 0.25M, 0.5M, 1M or 2M in the measuring cylinder and poured it into the conical flask.
- Then we weighed out 0.5g of medium marble chips, making sure that the surface area is not different or the mass, as if these are changed the results will not be as reliable.
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Next we put the marble chips (calcium chloride) into the acid in the conical flask, this has to be done very fast and the bung be put on straight away as to make it a fair test little gas (CO2) should escape.
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We then proceeded to take measurements of the volume of CO2 produced every 20 seconds for 10 minutes (600seconds).
- We decided to do it for 20 seconds because we know that some of the reactions would be slower than others and the volume of gas needs to be noted quite often
Variables and constants
In our investigation the things kept constant will be; the mass of marble chips (0.5g), the volume of hydrochloric acid (20cm³), the equipment. The variable in our investigation is the concentration of HCl. Two things that we will also try to keep constant is the surface area of the marble chips, however this can sometimes be hard to achieve and the temperature of the mixture (room temperature). If we changed any of these constants it would really affect our results, proving them to be unreliable. The independent variable will be the concentration of acid; therefore the dependant variable is the volume of carbon dioxide produced.
There will be only one independent variable as if there is more than one the test will not be fair and the results will be invalid. The four different concentrations are 0.25M, 0.5M, 1M and 2M. After looking at our preliminary results we decided to use a range of different concentrations so that we could get a better picture of the rate of reaction throughout different molars of HCL.
Health and Safety
From the lab’s hazard card we have gathered that throughout the experiment eye protection must be worn as hydrochloric acid is a highly corrosive and toxic chemical that can be very dangerous if it gets into your eyes or on your skin. Also there must be no eating or drinking in the lab at any time, and all bags and coats must but underneath desks to prevent people tripping over and potentially causing accidents involving harmful chemicals such as Hydrochloric acid.
Prediction
By referring to our preliminary results I can predict that the higher the concentration of acid the faster the rate of reaction. I think this because of the collision theory which states that particles with more surface area in relation to their volume have more particles available for collisions, and the more collisions there are the faster the rate of reaction.
Results
Results for 0.25M:
Observation:
The rate of reaction was very slow, which was probably due to the concentration of acid being 0.25M which is quite weak.
Results for 0.5M HCl:
Observations:
Here the results are mostly similar, accept form Test 1, it is highlighted as an outlier because its results are significantly higher than the other three. This is probably down to the surface area of the marble being greater than the other two; consequently this result will be discarded and not used in calculating averages.
Results for 1M HCl:
Observations:
This reaction went quite fast, which means that that the rate of reaction was fast. This was because of a high concentration of hydrochloric acid.
Results for 2M HCl:
Observations:
Here we observed that there was an outlier (Test 3) which did not follow the pattern of the other three sets of results. I think that it is an outlier because when we did the experiment there was one piece of marble that did not fizz like the others were; this reduced the amount of CO2 produced and slowed down the rate of reaction.
Gradients
What I found out
I found out that as the concentration of the hydrochloric acid increased, so did the rate of reaction. This is proved by my graphs which show the highest volume of CO2 for 0.25 M acid as 7cm³, while the highest volume of gas for 2M was 100cm³. I calculated the gradient for the all start of the reactions (at 120 seconds), and I found out that the higher the concentration of acid, the higher the gradient.This proves that the lower the concentration of acid the slower the rate of reaction, however the gradients did not agree with this pattern 2M should have had a bigger gradient than 1M however 1M was larger than 2M. This could have been due to several factors; the tests were done one different days, meaning the 1M tests could have been done at a higher temperature, meaning higher chance of collision and faster rate of reaction. Another reason could be that the the surface area of marble for the 1M test may have been larger than the surface area of the 2M test. My findings can be linked to the collision theory...
The Collision Theory
For a chemical reaction to occur, the reactant particles must collide. But collisions with too little energy do not produce a reaction. The particles must have enough energy for the collision to be successful in producing a reaction. Only particles which collide with enough energy will react when they collide. The rate of reaction depends on the rate of successful collisions between reactant particles. The more successful collisions there are, the faster the rate of reaction. In our experiment we varied the concentration of the acid, this means that the higher the concentration of the acid, the greater the chance of particles colliding, and the more particles collide the faster the rate of reaction.
Evaluation
In the preliminary work we used two different methods,the gas cylinder and the beehive shelf, we decided to use the gas syringe because the results seemed a lot more concise and it was a lot less complicated to use, leaving less room for human error. Proof that the gas syringe was more accurate is shown in one of the preliminary graphs where you see the values as being considerably higher due to less gas lost. We found next to no problems with the gas syringe, however the only thing was that you had to make sure that the syringe or the tube wasn't faulty, or else gas could have been lost, ending in an outlier result. I don't think that the beehive shelf would have been a better option because it was less accurate and it was a lot harder to set up than the syringe. In order to achieve results that were as accurate as possible we used the gas syringe.
The range bars on my graphs all followed a similar pattern;they started of small got bigger and then were small again. I think that from the range bars my results are fairly accurate, however some of the the range bars are a little too big for the results to be really accurate, if I were to repeat this experiment I would make sure that my data was as accurate as possible.
One weakness in our data was the sometimes large range of values that made the results less accurate,another weakness was the outlier results. We had two results that were significantly different to the other sets of results, this was down to faulty marble and increased surface area of the marble, in future we would go back and redo these results so that we could have a more accurate result and could have used then in the average and range.
I think that repeating the experiment four times was a good idea, however to achieve optimum accuracy it should have been repeated at least six times. Also during our preliminary results we saw that the reaction had not finnished after 300 seconds, therefore we decided to time ours for 600 seconds, this gave the reaction a longer time to end. If we had done the investigation again we woul have made sure that we recorded values for over 600 seconds, made sure that the temperature is the same every time, made sure that all equiptmen is working correctly and also made sure that the surface area of the marble chips reamins the same throught out to ensure accrate reaults.
In conculsion I think that my results are not reliable, this is because the range of reauts are too varied. Although my results did follow the expected pattern (as the concentration of acid increases, the rate of reaction increases) the gradients did not follow the patttern the were meant to, this was because the results were too varied and not consise enough. Therefore the results cannot be reliable.
