- Concentration of acid- There will be more acid particles in the solution if you increase the concentration of acid, so the chance of them hitting the marble increases, so the reaction gets faster.
- Surface area- There will be a faster rate of reaction if there is a greater surface area compared to a smaller surface area.
- Catalyst- A catalyst increases the rate of a chemical reaction without itself being used up. Catalysts are usually transition metals. In the presence of a catalyst, less energy is needed by a collision in order to be successful. Therefore, there are relatively more successful collisions and so the reaction rate increases.
had to be kept constant. Firstly, I will keep the calcium carbonate in a powdered form and will try to make the mass as similar as possible. I will achieve this by weighing the calcium carbonate to be at an approximate mass of 2g on a top pan balance. From a previous experiment I did involving different sized marble chips I found out that the surface area greatly affects the rate of reaction, therefore I will spread the powder as evenly as possible. Another variable I took into account was the volume of hydrochloric acid which I will use; I am changing the amounts of acid in each concentration. For example, 50ml of acid with 0ml of water, 40ml of acid with 10ml of water and so on until 10ml of acid with 40ml of water. I could not control the room temperature but I assumed that the room temperature would stay around the same for the duration of the experiment. I will start timing the collection of the gas once I have replaced the bung on top of the conical flask. After deciding how to approach all of the variables in the experiment, I decided to use different concentrations of hydrochloric acid in this experiment and decided to carry it out. Firstly I filled a measuring cylinder with 50ml of Hydrochloric acid. I put 2g of Calcium carbonate into a conical flask and then I mixed both substances together. I then quickly put the gas syringe into the conical flask and started to collect and record the data. I did this again but this time I did it with 40ml of acid with 10ml of water and so on.
Prediction
Some chemical reactions are finished in a tiny fraction of a second and some can take millions of years. A reaction which takes place in a very short period of time is called a fast reaction. One which takes place over a long period of time is called a slow reaction. In this investigation I predict that the solution with the high concentration of acid will have a much faster rate of reaction than the weaker solution. I have predicted this from my knowledge of a previous experiment and scientific knowledge. I think that this will happen because the more hydrochloric acid in the solution, the greater the solution and there will be more particles colliding and more energy, therefore a faster rate of reaction. The reason I think that the rate of reaction will increase is that the experiment is exothermic and will give itself energy through the heat which will increase the rate of reaction. An exothermic reaction is a reaction which produces energy. For example, a mixture of iron and sulphur is heated in a Bunsen burner flame, the mixture starts to glow. The glow spreads through the mixture, even if the flame is removed. This is because, energy is being given out. So, I predict that as the concentration of acid decreases there will be fewer effective collisions between the acid and calcium carbonate.
Results
Test 1
Test 2
Test 3
Average
Conclusion
After looking at my results and graph I am able to conclude that the more concentrated the acid the quicker the reaction happened. There was a dramatic change in the amount of seconds that it took to collect the gas as more water was added to the solution. For example, if you look at the graph, it shows how much longer it takes for the gas to be collected in the second half of the concentrations than the first half. As I look at my results, the more diluted the solution is the longer it takes for the gas to collect. Before I did the experiment, I made some predications that the more concentrated the acid was the quicker the reaction would happen and more carbon dioxide would be produced. This was completely correct because what I thought would happen, did. At this point we are able to answer our main question, which was ‘how does changing the concentration of acid affect the rate of reaction between hydrochloric acid and calcium carbonate.’ The answer to this would be that changing the concentration of the acid will either make it go slower or quicker and more or less gas would be produced depending on whether the concentrations were more or less. These factors affect the number of collisions of reactant particles, and this effects the rate of the reaction. A rate of reaction is the rate or speed at which a reaction takes place. For a reaction to occur, such as this one with hydrochloric acid and carbon carbonate, not only must particles collide with each other but they must have enough energy so that original bonds are broken and new bonds formed. The energy needed to break a mole of bonds is known as bond energy. If the collision has insufficient energy no reaction occurs. Also, reactions can only occur when atoms or molecules approach close to each other physically, in what is called a collision. When they approach close to each other in this way, they can exchange electrons. It is the moving of electrons from one atom to another that results in a reaction. If the number of collisions per second increase then the rate of reaction will increase. If a solution is made more concentrated, then there are more reactant particles per set volume. This makes collisions between the reactant particles more likely. Therefore, there will be more collisions per second (as shown on the diagram). In other words, the rate of reaction is increased.
If there are more particles (more concentrated) they are more likely to collide and react. Twice as many particles, (double concentrated) the reaction would be twice as fast.
More concentrated Less concentrated
Evaluation
I feel that this was a successful experiment. My results seem to indicate a clear pattern from which I was able to confidently draw a conclusion. This conclusion confirmed my hypothesise. The method that I used produced my results accurately and quickly enough to finish the experiment in the allotted time. My results were reliable, as the experiment was a fair test. I ensured that this was true by keeping all of the variables not involved in my experiment constant. I could not control the temperature at any time in the reaction except for at 0 seconds. This is because the reaction released thermal energy. I can say that no other energy was deliberately put in or taken out of the contents of the conical flask during the experiment. I used roughly the same mass of marble throughout the whole experiment, this kept the surface area constant, but something unexpected happened. I had a problem with my method in that I had to drop the acid into the conical flask, place the bung into the top and start the stopwatch. This is such a long sequence of activities to do in the time it takes for the acid to hit the marble. I think that this is the reason for the abnormalities in my results as I did not start the stopwatch at the correct time because I had trouble putting the bung into the conical flask. Also, when I was putting the calcium carbonate in the conical flask it was sticking to the bottom because the flask was damp so to resolve this problem if I were to do it again I would dry it properly or use lots of dry conical flasks. I have already mentioned the problem of the gas having to push itself up the delivery tube before it was collected. This added time onto the true time taken. This means my results are higher then they should be. The truth of my conclusion is not undermined by this however, as the same effect happened to each test. I could overcome this problem and the one mentioned before by only starting the timer when the gas starts to fill the measuring cylinder. This would not include the time taken to push the gas up the delivery tube in my results, and I would not have to start the stopwatch at the same time as putting the acid in the flask. To provide more evidence for my investigation I could use a thermometer to measure the temperature during the experiment, this would show whether my theory of the lower concentration not heating up the reactants is true or not. For further investigation, I could use stronger acid to see if there is a limit to how quickly the reaction can take place. Also, I could measure the mass loss of the reaction by having the conical flask on a top pan balance. I could take away the mass at regular intervals from the original and find out how quickly the reaction takes place.
