In solutions of higher concentration, and in gases at higher pressure, particles are closer together. They have a greater chance of colliding and because there are more collisions, the reaction rate is greater.
Although I am investigating how the effect of the concentration of the hydrochloric acid affects the rate of its reaction with marble, there are other factors that may also affect the rate of the reaction, and in order to make my investigation more accurate and reliable, I will control these other variables and keep them constant.
The other factors (variables), which may affect the rate of the reaction of marble in hydrochloric acid, are:
- Temperature of hydrochloric acid. This will affect the rate of the reaction because as the temperature increases, the molecules generate more energy and move around quicker and collide with more energy.
- The surface area of marble chips. The bigger the surface area is, then the faster the rate of reaction because there is more of the substance for the particles to collide with.
Method: After I have set up all my equipment up safely and made sure that it will be a fair test I will:
- I will Measure 10cm³ of HCl (hydrochloric acid)
- Then I will measure 0.2g of CaCO3
- I will empty the 0.2g of CaCO3 in a conical flask
- Then I will Add HCl to the CaCO3
- Start the stopwatch
- I will then see how long it takes for the conical flask to fill up with gas. The faster it happens then the faster reaction. I will then record the results in a table.
- I will then repeat the experiment 3 times with the same concentrated acid so I can take an average to plot the graph.
- I will repeat it with different concentrations.
Results I collected: ~ what I have changed: concentration of acid.
Conclusion: what I have found from looking at my graph and what I think is happening:
What I have found out by looking at my graph is that the more concentrated the hydrochloric acid is, the faster the reaction and the less concentrated the hydrochloric acid is, then the slower reaction takes place. For example at concentration 2.0m the average time taken to collect a certain amount of gas 1.28 seconds where as 0.2m takes 41.59 seconds to collect the same amount of gas. This is because of my original theory based on the collision theory. Increasing the reactant concentration leads to an increase in reaction rate, and a higher concentration means a larger number of particles in a given volume. If there are more particles, there will be more collisions. More collisions will mean a larger number of successful collisions. Therefore the reaction rate will increase as it is proven here.
Evaluation
My results are not entirely accurate as when I repeated the experiment 3 times I didn’t gain the same results. I didn’t get any outstanding anomalous readings but there are 2 that don’t follow the trend curve. These are the average readings for 0.5m and 1.0. 0.5 is below the trend curve and 1.0 is above. I believe this is due to simply human error. Despite that minor error, the results I gained were enough to support my prediction.
Accuracy
My results were not entirely accurate as I didn’t get the same readings after repeating the investigation 3 times. Also, I had 2 minor anomalous readings due to human error. I could resolve them, or make it more accurate by 2 people taking the time and 1 person watching the experiment. I could have extended my results by using more and less concentrated hydrochloric acid. The pattern I can see is that of my theory. The increase of concentration of hydrochloric acid affects the rate of reaction. The results I got were accurate enough to make a firm conclusion.
Improvements
I would have changed the method to suit the experiment more, by doing the investigation over a longer period of time as this would make a clearer conclusion with more evidence. I would also get more people to take the time of the experiment; this could affect the overall conclusion and would be more accurate.
