Reacting an acid with a carbonate is safe, and it is easy to record the amount of carbon dioxide produced using an upside down measuring cylinder. I think this is the best reaction to study.
List of equipment:
- Conical flask
- Delivery tube with bung
- 50ml of Hydrochloric acid
- Clamp
- Electric scales
- Stop-clock
AND
- Measuring cylinder
- Large plastic tub filled with water
OR
The acid which was available for the experiment was hydrochloric acid (HCl). The calcium carbonate we were provided with was in the form of marble chips, in various sizes. We used the smallest ones because they have a larger surface area in contact with the acid, speeding up the process and it is much easier to weigh them out. In the preliminary experiments we found that the small marble chips reacted well with a 0.5M solution of hydrochloric acid and water, so we felt it unnecessary to use the 2M solution of hydrochloric acid and water.
It already had enough activation energy, so we didn’t need 2M acid. Activation energy is the minimum energy required for a reaction. The peak shows the point where enough energy has been made by two chemicals. The energy then gets released until no potential energy is left. Potential energy is stored energy which could be used in a reaction.
There were two different methods we tried in our preliminary experiments. One of them involved a glass gas syringe:
Method for the first preliminary test:
Secure a glass gas syringe onto a metal clamp. Push all of the air out. Connect to a delivery tube. On the other side of the delivery tube, have a conical flask with calcium carbonate and hydrochloric acid reacting in it. There must be an airtight seal using a bung. Time it with a stop clock. Every ten seconds, record the amount of air inside the glass syringe.
This experiment didn’t work very well because the plunger got stuck, so there were no results.
It is also dangerous as it is made of glass.
The second experiment involved putting a certain volume of water into a measuring cylinder and turning it upside down in the water. When carbon dioxide came through the delivery tube, it travelled to the air space, making it increase in volume. It was easy to measure how much carbon dioxide was released every ten seconds.
Method:
Half fill plastic tub with water. Put measuring cylinder into the water upside down. Put one end of delivery tube into it. Get ready to put the end with the bung on into the conical flask. Put a measured amount of small marble chips into a conical flask, then add a measured amount of hydrochloric acid. Put the bung on, start, the timer and measure amount of air space every 10 seconds for three minutes.
This preliminary experiment worked successfully so we decided to use it for our experiment.
The results were very consistent and promising.
Method for real experiment:
Put on goggles. Tuck in stools and keep bags out of the way. Half fill a plastic container with water. Use electric weighing scales to measure out 2-10g of small marble chips (different amount for each experiment). Pour 50ml of 0.5M HCl into a beaker. Pour 10ml of this into a measuring cylinder (10ml for each of the five experiments). Fill up another measuring cylinder with water and put it upside down in the tub, connect it to the delivery tube. Put the marble chips and HCl into a conical flask, start the timer immediately and put the bung on. Record how much gas there is every 10 seconds for 3 minutes.
My partner read out the reading on the measuring cylinder every ten seconds, when I told him it was time to. Then I carefully noted down the results in my book. We made sure our results were reliable by repeating all five of them three times.
I predict the more marble chips there are, the faster it will react. This can be explained with the collision theory of kinetics. The more molecules there are, the more collisions there will be, which speeds up the process. In this case it is the CaCO³ and HCl. The more marble chips there are, the more collisions there will be, creating more reactions.
I also think the amount of marble chips used will not make a difference to the total volume of carbon dioxide at the end. This is because in our preliminary experiments, some of the marble chips didn’t react, meaning there wasn’t enough hydrochloric acid for it to react with. It was meant to bubble and fizz. If the acid concentration was 2M, there would be a lot more activation energy, as it could reach the minimum amount for a reaction easier. However, if they do not react, the particles will collide, and then bounce off each other.
We carried out each of the five experiments 3 times for accuracy. The results varied because the amount of HCl was never completely accurate and some Carbon dioxide was lost if the bung wasn’t put on quick enough. Here are the results:
These results show that the more marbles chips are present, the faster the reaction will be. This proves the collision theory of kinetics is correct. The more particles present, the more chance of a successful reaction. The experiment doesn’t show what activation energy is very well, as it is more to do with stronger and weaker concentrations of chemicals, not the amount you use.
Reaction of 10ml of HCl with 6g of Small marble chips
Test 2 with 8g clearly went wrong so I chose to ignore it and average the other two. This was probably due to escaping gas at the start.
The more marble chips there are, the faster it will react. This can be explained with the collision theory of kinetics. The more molecules there are, the more collisions there will be, which speeds up the process. In this case it is the CaCO³ and HCl. The more marble chips there are, the more collisions there will be, creating more reactions.
The amount of marble chips used did not make a difference to the total volume of carbon dioxide at the end. They ended up with different amounts of carbon dioxide, but it had no correlation to the amount of marble chips used.
This chart shows that the more marble chips are present, the quicker the reactions will take place. This can be seen by the steepest gradient at the start for the 10g one and the least steep gradient for the 2g one. Only the first few intervals are important on this graph as they all end up on different amounts of carbon dioxide which isn’t directly relevant to the amount of marble chips. I expected the 4g and 6g experiments
Evaluation:
The experiment was accurate and inconsistent for several reasons. These include amount of marble chips, amount of HCl, how quickly the bung was put on and the accuracy of the person reading the measuring cylinder. The method we planned proved easy to follow. We did not have to modify it as we went along.
Our results were quite reliable; we did each one three times so the average would be more accurate. There was definitely positive correlation in the graph and a clear curve. I feel the results are reliable enough to make a valid conclusion. The more marble chips there are, the faster a reaction will occur.
The amount of HCl should have been more carefully measured out because even 1ml can make a difference. The main problem was putting the bung on quickly. If it was left too late, a lot of carbon dioxide could escape. To solve this problem, a better fitting bung could be used. The problem with the measuring cylinder was it was hard to read upside down. It had to be read with utmost care.
If I was to conduct further experiments related to the reaction rate of acids and carbonates, I could use sulphur dioxide and marble chips. It would hopefully back up the statistics found in this experiment. I could also see how much temperature affects the rate of reaction, to further investigate the collision theory of kinetics. To find out more about activation energy, I could conduct an experiment which tested different concentrations of HCl and water. My prediction for that experiment would be the more concentrated the HCl was, the quicker it would react.
To conclude, the hotter the acid is, the quicker the reaction will take place between the marble and the acid, due to the collision theory of kinetics.