Once I have collected 40cm³ of carbon dioxide I will stop the clock. The time that it has taken to collect the 40cm³ of carbon dioxide will be recorded into my table. Then repeat the experiment again. If the range in difference is higher then 10, I will do the experiment a third time till I have a range lower then 10. I am going to repeat the experiment 10 times, as I am going to do five different temperatures twice, so that I get more accurate results.
If the temperature of the hydrochloric acid is too cold then I will heat the conical flask which will be filled with the acid over a Bunsen burner. Once it is at the right temperature, I will continue with the experiment. If the hydrochloric acid is too hot however, I must cool it. I will do this by putting the conical flask in the tough of water then taking it out to check the temperature. Once it is at the correct warmth I will proceed with the experiment.
Detailed Method
The variable factors in my experiment are the concentration of acid, weight of the limestone, the temperature of the acid, the surface area and volume of the acid.
To see if the temperature does affect the rate that limestone dissolves in acid, I will see how long it takes to produce 40cm³ of carbon dioxide. This will indicate how fast the reaction is taking place, as the quicker the carbon dioxide level increases to 40cm³, the faster the limestone is dissolving.
The only variable factor I will change is the temperature. This is so that every time I repeat the experiment it will be fair as I’m only changing the factor that I want. I am only changing the temperature as I am going to prove that temperature increases the rate that limestone dissolves in hydrochloric acid.
I am going to keep the concentration of the acid the same, the weight of the limestone, surface area of the limestone and the volume of the acid all the same so that the experiment is fair.
By increasing the amount of limestone pieces I would be increasing the surface area. This would increase the possibility of the hydrochloric acid particles colliding with the limestone which would increase the rate in which the calcium carbonate
Stephanie Fletcher
dissolves in acid. I am seeing if the temperature of the acid does increase the rate in which limestone dissolves in acid not the surface acid.
If I amplified the volume of acid each time I did the experiment then the rate in which the limestone dissolved in hydrochloric acid would increase. This is because there are more hydrogen chloride particles so the chances of a collision occurring between the acid and limestone increases. The same is if I decreased the amount of acid each time. The rate of limestone dissolving in acid would decrease because the likeliness of the hydrochloric acid particles colliding with the limestone is low.
The weight of the limestone would too increase the rate of limestone dissolving in hydrochloric. This is because there is more of the limestone, so the chances of a collision happening between the calcium carbonate particles and the hydrogen chloride increases.
The concentration of the acid has an affect on the rate in which calcium carbonate dissolves in hydrochloric acid. As there is more acid there are more hydrogen chloride particles so there is more chance of a collision between the limestone and acid. If the concentration of the acid was less then the experiment before, the rate in which the limestone dissolved would be less because the possibility of a collision occurring would be lower as there aren’t as many particles as before, so the test wouldn’t be fair.
Preliminary Investigation
Aim:- To set the variables I will keep the same constant and to decide the temperature range I will use.
Limestone weight = 1.5 grams
Number of limestone pieces = 4
Acid concentration = 1 M
Acid volume = 50 cm³
Gas volume = 40 cm³
Time to collect gas at 20°C = 182.4 seconds
Time to collect gas at 60°C = 16.92 seconds
Temperature range = 20°C - 60°C
Stephanie Fletcher
A Table To Show How Changing The Temperature Affects The Rate Limestone Reacts
I added another row to my table as I had an anomalous result. This means that the 40°C experiment did not fit onto the graph when I plotted my results. So I re-did the experiment and I recorded my results and plotted 58.57 seconds onto the graph. This was still an anomalous result so I left the graph as it was, as the previous time for 40°C time was closer to the line. If I had more time then I would have checked the 30°C temperature to see if that made a difference to my curve line.
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Conclusion
In my experiment I added 4 pieces of limestone to the 50cm³ of hydrochloric acid and recorded the time it took to collect 40 cm³ of carbon dioxide. The hotter the temperature got the faster the limestone reacted with the hydrogen chloride. The hydrochloric particles would get more energy from the heat and therefore they would be more active. This would increase the chances of a successful collision happening between calcium carbonate particles and the hydrochloric acid as they will collide with more force. A successful collision is when the acid particles collide with the limestone and break the bonds.
I did think that as the temperature increased the time it took to collect 40cm³ of carbon dioxide would decrease. My prediction of that the hotter the temperature of the acid the quicker the limestone reacted was proven right. I think that this was because the more energy the hydrochloric particles got from the heat the bigger the force they used when they collided with the limestone. As the hydrogen and chloride particles collided with the calcium carbonate successfully the bonds broke and they separated. The separated particles then joined with other particles and formed carbon dioxide, water and calcium chloride. As I increased the temperature the particles obtained more power every time I repeated the experiment at different temperatures. Therefore, more successful collision happened and the limestone dissolved in the hydrochloric acid quicker.
After constructing my graph to show how changing the temperature affects the rate limestone dissolves, the plots form a negative correlation, which is what I expected. The graph shows that as the temperature increases the time taken to collect 40cm³ of carbon dioxide decreases. I expected that the line would be a curve and not a straight line because it’s impossible to get a temperature where it doesn’t take any time for the limestone to react. I can tell this by carrying the line on, I see that there isn’t a point on the graph where there isn’t a time and temperature where the limestone doesn’t react.
Evaluation
My experiment worked well proving that the higher the temperature the quicker the limestone dissolved in acid. I was able to solve my problem by carrying out the experiment and recording my results in the form of a table and graph. This then gave me the indication of that the higher the temperature the quicker the limestone dissolved as there was a negative correlation in the graph.
I found a number of errors in my investigation. I could tell that I had made some errors in my experiment by looking at my graph. I got an anomalous result, therefore I had a temperature that had a change in the variables but accident. To prevent errors occurring I did the experiment twice, or if the two times didn’t have a range of ten then I did the experiment again till they did. I then found the averages of the two results to get more of an accurate result. By doing the experiment more then twice this shows that there is an error.
The variables could of not be controlled properly every time I repeated the experiment, therefore this would of caused errors in the experiment. It is very difficult to
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do, and the measuring is only to the eye which isn’t accurate enough. Procedural problems would have also caused errors and affected my results.
There are a number of procedural errors that occurred during my investigation. When I did the experiment the equipment might have not been air tight, therefore carbon
dioxide was leaving through the top of the conical flask as well as the delivery tube. Then when I repeat the experiment, the bun could have been air tight, so the amount of carbon dioxide going to the conical flask was at its fullest, so the time it took to collect 40cm³ of gas was less then when the bun wasn’t air tight. This would have affected my results as when the bun was air tight the time it took collect the gas was a lot less then if the bun wasn’t air tight. To prevent there being a difference in the equipment being air tight I could have greased the bun, or used the same bun and flask every time I did the experiment.
Another procedural problem that aroused during the investigation was that I used different bottles of acid. This is a problem because one bottle of acid could have been 0.95m and another 1.05, therefore one was more acidic then the other. This would have the effect that the reaction would take place faster even if the temperature was the same and the concentration as the experiment before. This is because the particles in the hydrochloric acid have more energy in them so increase the chance of a successful collision. To prevent the hydrochloric acid being more acidic then the experiment before I could have used the same bottle of acid every time I did the experiment, by labelling the acid with my name on so know one else used it.
By using different thermometers every time I repeated the experiment would have affected my results. This is because not all thermometers are the same and have a difference of either + 1°C or - 1°C. This would have made a difference to my results as when I was trying to get the hydrochloric acid at the correct temperature it could have been 1°C more or less, compared to another thermometer. To avoid the hydrochloric acid being at different temperatures when I repeated the experiment, I could have used the same thermometer so then my experiment would have been correct to my thermometer.
The weight of the limestone would have had an affect on my results because the heavier the limestone pieces the quicker they would react with the acid regardless the temperature. The size of the pieces would also have the same affect on my results as the weight of the limestone would. The bigger the surface area the more space they take up so the chances a collision between the acid and calcium carbonate increase. To prevent the limestone dissolving in the hydrochloric acid quicker because of the change in limestone weight and surface area I could have powdered the limestone and weighed it like that. I could just take some away and the surface area would have sorted its self out each time I repeated the experiment, so as long as the weight was the same then the surface area would too be the same as the experiment before.
Every time I started the timer I would have added an error into my investigation. This is because I never started the timer at equal times. Sometimes I would have started it at the first sign of a bubble and others it would have been the first thing I put the end of the delivery tube into the measuring cylinder. This would have changed the time it took to collect 40cm³ of carbon dioxide because I never started the timer when the gas was
Stephanie Fletcher
collecting. To make it a fair test every time I did the experiment I should have started the
time at equal times. For example I could have started the timer 5 seconds after putting the end of the delivery tube into the measuring cylinder, every time I did the experiment.
I wanted to collect 40cm³ of carbon dioxide each time I repeated the experiment. However it is hard to tell that I have collected the same amount each time I did the
investigation as the level of water wasn’t straight so I couldn’t tell if it was 39, 40 or 31cm³ of carbon dioxide I had collected. This would effect the time it took to collect the gas because I didn’t stop the timer until I collect 40cm³ of gas. If it was less then 40cm³ then the time to collect the gas would be a lot less then it should really be, if the it was more then 40cm³, then the time to collect the gas would be a lot more then it should have been. To prevent my getting an accurate time I should have concentrated more or collected more then 40cm³ of carbon dioxide. By collecting more gas I deceased the percentage of collecting more gas.
In my graph I had an anomalous result. This meant that one of the times wasn’t accurate enough and I had made a huge error. I re-did the temperature but still got an anomalous result, so I left the pervious time as it was closer to my curve. If I had more time then I could have redone the section between 30°C and 40°C. I would have done more temperatures in between these and then plotted these results and joined up a curve to get rid of the error. For example 30°C, 32°C, 34°C,36°C, 38°C and 40°C.
