The experiment was carried out using 25ml hydrochloric acid and 25ml calcium carbonate. The student tested the solution three times, once using small marble chips, once using medium ones, and once using large ones. The student decided to use medium marble chips in the actual experiment because they were of average size. The experiment was carried out using various different amounts of marble chips ranging from 2g to 10g. After the results showing that the more marble chips that were present, the faster the reaction would go, the student decided to use 5g of marble chips to allow enough time for the reaction to be seen and the results recorded but made sure that the reaction would not go on for too long and waste time.
Apparatus:
- 2 bosses
- 2 clamps
- 1 glass trough
- 1 set of digital weighing scales
- water
- 465ml hydrochloric acid
- 1 delivery tube
- petroleum jelly
- 75g medium marble chips
- 1 conical flask
- 2 retort stands
- 1 stopwatch
- 2 measuring cylinders (50ml)
- 2 beakers
- tissue paper
- 1 pair safety goggles
- 1 paper funnel
- 1 weighing boat
Diagram:
Method:
The apparatus will be set up as shown in the diagram. 5g of medium sized marble chips will be put into the conical flask and 50ml of the correct solution will be put in afterwards. As soon as the solution goes into the conical flask, the glass bung must be placed firmly into the top of the conical flask and the timer must be started. Every time the water in the measuring cylinder goes down by 10ml the time will be recorded. This will be repeated three times for each concentration of solution.
The different concentrations of solution to be used are as follows…
50ml hydrochloric acid: 0ml water
40ml hydrochloric acid: 10ml water
30ml hydrochloric acid: 20ml water
25ml hydrochloric acid: 25ml water
10ml hydrochloric acid: 40ml water
Variables:
- The amount of solution in the conical flask.
- The amount of calcium carbonate in the conical flask.
- The concentration of the solution being tested.
- The temperature.
These are the factors which could be varied in the experiment. The only factor that will be varied is the concentration of the solution. All of the other factors will be kept constant.
Changes:
The student will have to make these changes to the experiment due to information gained during the preliminary experiment.
- Petroleum jelly must be applied to the bung before it is put into the conical flask to ensure a tight fit and to ensure that none of the gas escapes out of the conical flask.
- The measuring cylinder must be full of water when it is placed upside down into the trough of water.
- The same person must judge when the measuring cylinder has lost 10ml of water because people have different opinions.
Fair tests:
To ensure that the experiment is a fair test the student must…
- Make sure that the concentrations are correct.
- Make sure that the apparatus is set up properly each time the experiment is carried out.
- Make sure that the timer is switched on at the same point each time the experiment is carried out.
- Make sure the bung is firmly inside the conical flask each time the experiment is carried out.
- Make sure that the same amount of marble chips is used in each part of the experiment.
- Make sure that the temperature stays the same all the way through the experiment.
- Do the same number of repeats for each of the concentrations.
Safety Precautions:
To make sure the experiment is safe to carry out the student must…
- Wear safety goggles at all times.
- Take care when handling acid.
- Take care when handling glass equipment especially the delivery tube which is easily broken and the trough which is very heave when filled with water.
- Wash hands when the experiment is over.
- Do not run or eat in the lab.
Results:
Repeat 1:
Repeat 2:
Repeat 3:
Average:
Skill Area A:
Trends:
- Each time the experiment was carried out the solution of greatest concentration had the fastest rate of reaction.
- As the concentration was increased the amount of collisions also increased.
- As the amount of collisions increased so did the amount of successful collisions.
- Time is directly proportional to the volume of carbon dioxide given off.
In conclusion….
The higher the concentration of acid in the solution the faster the reaction took place.
On a few occasions during the experiment, anomalous results were obtained due to the constants changing slightly or the collisions occurring were not successful and the particles just bounced off each other.
The conclusion reached supports the original prediction made. As the concentration of acid in the solution was increased, the rate of reaction became faster.
Errors:
Using scientific knowledge it can be determines what may have gone wrong in the experiment to produce anomalous results.
- Sometimes when particles were colliding they may not have had enough energy and just bounced off each other instead of reacting.
- Some air may have been trapped in the top of the cylinder before the experiment began, this would mean that all of the results are incorrect.
- The bung in the delivery tube may have been leaking. This could have caused some gas to leak out and would have lead to inaccurate results.
- The reaction may have started before the bung was replaced meaning that some of the gas would have escaped out of the conical flask, giving inaccurate results.
Skill Area E:
In my opinion, the experiment went well. A sufficient amount of readings were taken although it would obviously have helped to have an extra set of results. The results may not be entirely accurate as each concentration should have ended on the same amount of gas but in the higher it should have only taken a shorter time than in the lower concentrations. I think this happened because too much carbonate was used in the acid, it could not collect as much gas as it is able. Also the carbonate could not get into the acid and the bung could not be placed in position without losing some gas, which is an important fault in the experiment that could cause all the results to be inaccurate.
There were a number of anomalous points which are circled on the graph, these can be explained by a poor reading, or a build up of gas entering the measuring cylinder quickly.
Some of the results gained during the experiment were anomalous. These factors could cause problems.
- The marble chips are not all the same size and their surface areas are all different. The dust on them would mean they were heavier than they actually are and even if they were washed before being used the water on them would mean that they were, again heavier than they actually are.
- The acid concentration can be kept constant perfectly but if you run out and need to make up some more, the concentration may not be exactly the same as before. This will cause inaccurate results.
Improvements:
If the experiment was to be carried out again the following improvements should be used:
- Instead of making up more acid every time it is needed, a large amount of each concentration of acid should be made before the experiment is started. This would ensure that the concentration of acid is always constant.
- When filling the measuring cylinder, to make sure no bubbles of air get trapped a sheet of plastic should be used to cover the top when filling it instead of your hand which lets water through it.
- A very clearly marked cylinder should be used as the reaction was sometimes too fast to get an accurate reading off of the poorly marked cylinder.
- When the marble chips are washed, they should all be bone dry before they are weighed and used in the experiment. This would ensure that the weights are exact.
- Although medium marble chips were used, they did not all have the same surface area. This meant that some were more prone to successful collisions than others. This could be solved by choosing marble ships of the same shape and size.
Further Work:
If we went on to investigate more about the rates of reactions we could choose a different variable for example temperature. We could keep the concentration constant and heat the solution to different temperatures to find out if heat increases the rate of reaction.
The same apparatus could be used except you would need a Bunsen burner instead of all the different concentrations of solution.
I could already make a prediction using knowledge from the previous experiment that the hotter the solution becomes, the faster the rate of reaction will be. This is due to heat making particles move more quickly, causing more collisions, more successful collisions, and a faster rate of reaction.