Prediction
In order for a reaction to occur, the reacting particles must collide. The colliding particles must collide with sufficient energy for a reaction to occur. The minimum amount of energy which they needed to have when they collide is known as the ACTIVATION ENERGY. If they have less than the activation energy, no reaction will occur when the particles collide. When the reacting particles collide with the activation energy, the collision is successful and a reaction occurs. The rate of reaction is higher when there are more successful collisions i.e. when more collide per second.
I think that if the concentration of hydrochloric acid will increase the rate of reaction. The rate of reaction will increase since there will be more H+ ions in the same volume of acid. Therefore, there will be more collisions every second between the carbonate ions and the H+ ions. Thus, there will be more successful collisions between the atoms and the rate of reaction will increase.
Quantitatively, if the concentration of hydrochloric acid is increased, I think the rate of reaction will increase since there will the more H+ ions in the same volume. Therefore, twice as many collisions will occur between the H+ ions and the carbonate ions. Therefore, there will be twice the number of successful collisions and the rate of reaction will be doubled.
I predict that the higher the concentration the faster the reaction will take place this is because in a higher concentration there will more hydrochloric acid molecules per set volume. This means that there will be a higher chance of the calcium carbonate molecules colliding with the hydrochloric acid and reacting. This should in theory increase the rate of reaction as the concentration is increased.
The reaction rate, however, should decrease as the experiment progresses because as the reaction time increases the number of hydrochloric acid molecules present will decrease as they have been reacted to form water calcium chloride and carbon dioxide. The additional water and calcium chloride present as the experiment progresses should decrease the rate of reaction because of decrease in concentration. This should make a graph of the reaction curved as the reaction rate slows down.
The increase in the concentration should be directly proportional to the increase of the reaction rate at a given time. This is because by doubling the number of hydrochloric acid molecules present the chance of a collision should be doubled, as there is now twice the possibility of a collision-taking place initially.
Diagram
The values for my preliminary experiments
Out of the powdered calcium carbonate, the large calcium carbonate chips, I chose small calcium carbonate chips. I decided that for my preliminary tests that I will use 20cm³ of distilled water and 20cm³ of hydrochloric acid. For my first experiment, I will use 0.55g of calcium carbonate small chips. In the second experiment I will keep the distilled water and hydrochloric acid at the same volume and increase the mass of the small chips to 1.00g.
Here are the values for my experiment, in the second column you have the volume of CO2 released with 0.55g and in the third column you have the volume of CO2 released in 1g.
I have chosen 1g of small calcium carbonate chips as it is a reasonable rate, especially as I have decided that I will only need 150 seconds for my experiments. As the experiment finished at 140 seconds with 1.00g of calcium carbonate small chips, I feel that this is a good mass.
I decided as a result of my preliminary tests that I will be studying the rate of reaction with concentration. I will vary the amount of hydrochloric acid and water and will keep the mass of calcium carbonate small chips the same. Also, I though that 0.55g of calcium carbonate was too little for the reaction to take place over a decent period so 1.00g of calcium carbonate chips, will be best. I will also try to find chops that are similar in appearance, as then my experiment will be more accurate
I have also chosen five concentrations that I am going to carry out as part of my coursework.
I will carry each of these experiments out three times. This is so that it will be a fair test.
Diagram
Apparatus – gas syringe, pipette, conical flask, distilled water, 2 molars of hydrochloric acid, retard clamp, 25cm³ measuring cylinder (6), calcium carbonate (1g of small chips), glass vile, stop clock, small calcium carbonate chips and a balance.
- I will wear my safety equipment – goggles and overall
- I will measure 1g of calcium carbonate small chips in a glass vile.
- I will measure it on a balance, but I first have to measure the vile on its own, and set the balance to 0.
- This is so that it only measures what is within the vile.
- I will then get six 25cm³ measuring cylinders.
- In this I will pour Xcm³ of distilled water in three of the cylinders and in the other three I will pour Xcm³ of 2m hydrochloric acid in three of the cylinders
- This is because I have to make it a fair test by doing it three times.
- If I go over, I will use a pipette to make it an exact amount.
- I will then get three large conical flasks.
- In each of the flasks, I will pour one cylinder of the distilled water and one cylinder of the hydrochloric acid.
- I will then set up the gas syringe and make sure that it is pushed in fully. Adjust the height of the syringe making sure that it is not too high or low.
- I will collect a stopwatch and make sure that it is set at zero.
- I will have the conical flask on the retard clamp so that as soon as I pour in the small chips of calcium carbonate I can push the rubber bung in.
- I will put the small chips in the conical flask, and I will begin to swirl the flask.
- I have to make sure I swirl it at a rate I can copy during the next experiment
- As soon as I put the chips into the solution, I will start the stop clock.
- From then on, every 10 seconds I will note down how much carbon dioxide has been given off.
- This will be done until a) all the small chips have been dissolved or b) the gas syringe reaches 100cm³ of carbon dioxide before it has all dissolved.
- I will repeat the experiment twice, with the same amount of acid and water.
- I will repeat this experiment with the different concentrations, each three times.
I will make it a fair test by making sure that I shake the conical flask at the same speed each time. Next, I will make sure that I measure all the hydrochloric acid and calcium carbonate small chips accurately. I will also make sure that I read the values on the gas syringe accurately, so that the graphs that I eventually draw up will be accurate. I am also going to make sure that I use to correct equipment, for example if I want to measure 20cm3 of hydrochloric acid I will not use a 50cm3 measuring cylinder, I will use a 25cm3 cylinder instead. This will ensure that the substances I measure out will be accurate. I will also make it a fair test by making sure that when I read the gas syringe for my results I am accurate, as it could ultimately affect my graphs.
I have also decided, based on preliminary tests that I will only take measurements of CO2 for 150 seconds. This is because with some values it could take very long for the calcium carbonate and hydrochloric acid to react. In addition, when working out the averages I have decided that if it goes into a decimal number I will round it up or down. So, if it is over, five we will round it up and if it is under, five we will round it down. If it is five, I will round it up. For example if there is the number 37.6, I will make it 38. If it is 36.5, I will make it 37 as well. I decided to record the amount of gas given off every 10 seconds. This is because we have only taken 150 seconds to monitor, so if I do it every ten seconds, it should give me enough data. I also worked out in preliminary tests that doing it every 20 seconds with some variables give too little data. I also must make sure that all the small marble chips that I use are roughly the same size, amount and mass, as if one is larger, it could throw the whole experiment off.
I will be keeping the mass of calcium carbonate small chops constant, the temperature at which the reaction will occur constant. However, the volume of hydrochloric acid and water used will alter with each experiment.
PART B: OBTAINING EVIDENCE
Experiment one - 40cm³ of acid and 0cm³ of distilled water and 1g of small calcium carbonate chips
I carried out the experiment as explained before – I used a gas syringe, three conical flasks a 50cm³ measuring cylinder to measure out the acid, and scales to measure the calcium carbonate small chips.
Experiment 2 – 35cm³ of hydrochloric acid and 5cm³ of water.
I carried out the experiment as planned before
Apparatus – I used a 50cm³ measuring cylinder for the hydrochloric acid and a 15cm³ for the water.
30 acid and 10 water
25 acid 15 water
30 water and 10 acid
To work out the final concentration there is a certain formula. This is Volume of acid multiplied by
2mole/dn3, divided by the total volume.
PART C: ANALYSIS
The first experiment does not fit in, i.e. it is an anomaly. It is not near any of the other values especially at 70 seconds it already reached 100cm³ of Co2, whereas in the other experiments, this is not the case.
This experiment was with 35cm3 of acid and 5cm3 of water.
There is a slight anomaly with one of the values, but when it came to the next reading, it matched up.
There were completely anomalous results for 1.75m of hydrochloric acid, so I decided not to include it.
An anomalous result
An anomalous result is a result is a result that is not near the other results i.e. it is irregular. An anomalous result should not be included in the average. An anomalous result can be caused if the solution was stirred differently i.e. quicker the first time and slower the second. Or, if the calcium carbonate small chips were not measured accurately or if there were a range of sizes. For example, if some chips are very small they would take a shorter time to break down compared to the larger chips, which would take longer. It can also occur if the acid and water were not measured accurately.
I have decided not to use one of my results in this. This is because it was anomalous and did not fit in with the rest of the values. Therefore, I have only varied four concentrations.
Initial Gradient
2m of hydrochloric acid –
- y/x = 57/70 = 0.814cm3/s
- y/x = 54/60 = 0.9cm3/s
- y/x= 58/70 = 0.829cm3
1.5m of hydrochloric acid –
- y/x = 59/70 = 0.843cm3/s
- y/x = 54/60 = 0.9cm3/s
- y/x = 65/70 = 9.29cm3
1.25 of hydrochloric acid –
- y/x = 42/70 = 0.6cm3/s
- y/x = 34/60 = 0.56cm3/s
- y/x = 42/70 = 0.6cm3/s
0.5 of hydrochloric acid
- y/x = 22/70 = 0.314 cm3/s
- y/x=16/60 = 0.26cm3/s
- y/x = 19/70 = 0.271cm3/s
Average Rate of Reaction
I have decided not to include 35cm3 of hydrochloric acid and 5 cm3 of water. This is because all the results were completely anomalous and will lead to the graphs not being accurate.
PART D: EVALUATION
The experiment I think went very well and I managed to get all the information I needed which I am very pleased about. The amounts of gas are not actually spot on accurate because as there was a time difference between realising when the time was 10 seconds and looking at the syringe. As my reaction time is slow. If I had more time make the readings, I will make sure that my testing is completely fair. This will be kept to a high standard by making sure that all the syringe measurements are more accurate. If the gas syringe had a more finer scale, my accuracy may have improved. However, it may be a bad idea as it could prove hard to read the syringe. The graphs and tables do show however the effects I wanted. The rate of reaction increases as the concentration of hydrochloric acid increases. If needed, I could still predict another similar experiment as this one gave me a lot of information. The graphs proved my predictions were correct, even though I had quite a few anomalous results. There are a number of reasons this could have happened.
- I could have measured my hydrochloric acid and water inaccurately.
- I could have measured the calcium carbonate small chips inaccurately.
- When plotting the times I could have looked slightly after the 10 second interval
- I could have read the gas syringe incorrectly.
- I could have swirled my conical flask quickly at one time, and slowly another.
- Another reason there might be anomalous results is because I used the same conical flask. This could mean some residue was left over, although I washed it.
- Also to make it more accurate I could have calculated the average speed for each concentration i.e. the amount of carbon dioxide produced per minute in centimetres cubed.
- It could also be inaccurate because I poured the calcium carbonate small chips into the hydrochloric acid and water, meaning some carbon dioxide was lost before I managed to place the bung on.
- The chips may have been on different sizes. If there were loads of small calcium carbonate chips but one that was slightly larger, it may take longer to break down the larger one, meaning the surface area was not the same in each case.
- The temperature may have also affected it, the room temperature may have been higher one day compared to another. This may have been because the heating was turned on. Or, if one day the window was slightly open to let some air in. This also could have affected it.
I think that bearing in mind all these things that could have gone wrong, it is not surprising that I was faced with all these anomalies. Not all results fit in with the others. Occasionally they do not seem consistent as you can see in the graph. Some results were so anomalous that I had to exclude them from my graphs as they would have given me inaccurate graphs, resulting in my initial gradients and final graphs being incorrect.
There are different experiments that I could have undertaken to do this experiment. One is to use a computer. This will measure the rate of reaction by measuring the loss in mass. The method is used if a gas is given off during the course of a reaction. As the reaction proceeds the container containing, the CaCo3 and HCl will reduce in mass as the carbon dioxide escapes into the atmosphere. The mass balance can be connected to a computer which continually records the mass and draw the graphs of mass against time. This method is more accurate since it enables readings to be taken and removes HUMAN ERROR. The advantages of this is that it produces a much better graph, it can do two things at once i.e. measure the loss in mass of the calcium carbonate small chips and record it in the form of graph. This would have been a more accurate result and it would have produced a graph for you. A burette may have also been a good idea, as it is easier to take readings from this. It is also a lot more accurate to measure the amount of gas given off.
In addition, other things that I would like to investigate would be the experiment of time against amount of gas produced to show at which points the rate of reaction was at best and the curve/line of reaction. I would like to also investigate other factors, which affect the rate of a reaction like temperature and surface area to see how they affect the rate of a reaction.
Some other areas in the experiment that I feel I could have improved on were factors like, controlling the stopwatch. There is lots of room for human error here. However, the inaccuracies due to them were negligible because I paid close attention to these during the experiment.
The results show that as the concentration of acid decreases, the time take for the reaction increases. As th time increases the rate of reaction decreases. The reason why the rate decreases as the concentration increases is that the number of H+ ions n the acid decreases as the concentration decreases. Therefore there are fewer collisions every seconds between the H+ ions and the Ca+ ions. Therefore there will be fewer successful collision and the rate of reaction will lower.
I that my prediction was proved. The reacting particles did collide with sufficient energy, as if they did not, no reaction would have occurred at all. The particles must have had the activation energy as without it no reaction will occur. Evidently one did otherwise I would not have obtained such results. The concentration of hydrochloric acid did increase the rate of reaction. The rate of reaction did increase because there were more H+ ions in the same volume of acid. Twice as many collisions must have occurred between 40cm3 of acid and no water compared to 30cm3 of water and 10 of acid.