Surface Area:
2
Temperature
2
Concentration
2
Preliminary Method
Firstly I set up the apparatus as shown under the apparatus but using a gas cylinder but this didn’t work, so I tried using a boiling tube however I ended up using a burette because the burette was more precise and left less room for human error. Originally I used 1g of calcium carbonate powder however the reaction was too fast to record and all 50cm3 of water was gone long before 35 seconds had passed. In response to this I tried with small chips only to find that the reaction, though slower, was still too fast leading to a high error margin which ended with getting results between 31cm3 and 37cm3 displaced. Due to this I tried using large marble chips which resulted in 22-25cm3 displaced. As this wasn’t accurate enough I tried using a burette instead of the boiling tube with the large marble chips which lead to results of 20-21cm3 displaced and as this was the most accurate results I had I used large chips and a burette.
Preliminary Results
Final Method
Firstly set up the apparatus as shown in the diagram below, and then place the CaCO3 in the HCL and use the stop watch to time how much CO2 is produced after 35 seconds. Once done repeat the experiment using different concentrations of HCL (diluted with water) with ratios of acid: water as shown:- 1:0, 9:1, 8:2, 7:3, 6:4, 5:5, 4:6, 3:7, 2:8, 1:9.
I decided on using a burette instead of a boiling tube or measuring cylinder because a burette is more precise and accurate, this is also the reason why I used a stopwatch instead of counting. Despite this they are not 100% accurate so some error margin in produced.
Factors involved in this experiment include temperature, concentration and surface area. The factor I have decided to change is concentration. I will be able to change this factor by diluting the hydrochloric acid with water and I will keep the other factors the same by monitoring the temperature to keep it at a steady rate and by weighing the large chips of calcium carbonate each time so the experiment is fair. I use large chips because it is a slower reaction and so will leave less room for human error.
I will use 10 different concentrations to increase the range of results and I will repeat the experiment three times for concentration to ensure any outliers can be found and discarded so to make sure that the data I will collect will be accurate and reliable, leading to a good quality of evidence on which to base my decision.
Hydrochloric acid is a strong mineral acid and is highly corrosive. Eye protection must be worn. Avoid ingestion, contact with eyes and skin. If any contact occurs seek medical attention.
Diagram
Results:
Explanation
Collision theory states that the rate of a reaction is dependant on the rate of collisions of particles with the correct geometry and energy. When such a collision occurs a reaction occurs thereby increasing the progress of the overall reaction. This is called a successful collision. To increase the rate of a reaction the frequency of successful collisions has to be increased. This can be achieved by increasing the number of those particles within a particular volume and therefore the chance that they will collide; this is what happens when increasing the concentration of an acid, as there are more particles per cm3. The effect concentration has on the rate of reaction is proportional meaning that if you doubled the concentration then effectively the rate should also double, this would result in a straight line in the results graphs. Trends seen from the graphs show a positive correlation however it is not proportional meaning that the rate is affected greater at higher concentrations compared to lower concentrations and thus reaction gets faster towards the end, making the gradient progressively more.
Conclusion
From this experiment I can conclude that the concentration of an acid does have an effect on the rate of reaction because of collision theory.
Evaluation
Due to human and apparatus error then the concentration has ~0.05cm3 error, while the rate has an error of ~ 1 second and 0.5cm3
The results aren’t proportional due to many factors. This experiment is exothermic and so the temperature increase may affect the results, also there is no way to get precisely the same surface area of calcium carbonate as they weren’t pre-cut to specification. The level of confidence in the results is low because of the many outliers in the lines of best fit because of this the data is insufficient and unreliable. Ways in which I could improve the experiment and results would be to carve out calcium carbonate chips to a specific surface area, while using a cooler to effectively reduce the temperature increase caused by the thermal energy being transferred.
Bibliography
1:
2: http://www.docbrown.info/page03/3_31rates.htm
