I am going to measure the rate of reaction by seeing how much time it takes to produce 100cm³ of CO². This will be timed by using a stopwatch.
I will use a gas syringe to gather my results because this is more accurate than the method of inverting a measuring cylinder in a trough of water to collect the gas produced, and then measuring displacement. The method using the gas syringe is also a lot easier to conduct, because there is less equipment to adjust.
Safety
In this experiment we shall be using hydrochloric acid, which is known to eat into living tissue, the eyes are especially at risk to damage from the acid. Because of this safety goggles should be worn at all times during the experiment.
Any acid that is split on the bench should be mopped up immediately so there is no chance of it coming into contact with the skin. Any spills on the skin should be washed of with water immediately.
Although the molar of acid we shall be using in the experiment isn’t strong enough to cause major irritations to the skin, it may cause some discomfort if it is not removed from the skin.
Fair test
To make sure that the experiment is conducted as fair as is possible. There are a number of factors, which we as scientists must control. Some are more difficult to control in the limited time window we have to conduct the experiment. These are:
Temperature – this is one of the harder variables to control, and we have decided to let this factor be unaltered by us. With heat it adds energy to the acid particles, and they move faster. Increasing the number of collisions with the marble chips. We can expect that on a hot day there will be slightly different results, with the reactions taking place in a shorter time.
Mass of marble chips – this variable is one that we must ensure remains the same. I have decided to use a mass of 10g marble chips. If the mass is not kept constant on all the experiments, we can expect the averages to be incorrect. If there is more chips used the reaction time will be shorter because there is more chips for the acid to collide with. If there are less chips the reaction time will be longer, because there will be less chips for the acid to collide with. I will make sure that the mass remains the same, by weighing the chips for each test on an electronic balance.
Volume of hydrochloric acid – if there is a greater volume of acid in the tests, the reactions times will be shortened, because there will be more acid particles to collide with the chips. The amount of acid I have decided to use is 10cm3. I have chosen this because it will be easy for me to make up the molars. To make sure that I keep this the same I will accurately measure out the acid in a measuring cylinder.
Size of marble chips – this is something we must take into consideration, although we do not have much control over it. A large chip size will react faster because it has a larger surface area.
Molar of the acid – even though we are changing the molar in this experiment, it is very important that the molar stays the same. And is not diluted or made stronger during each test. To ensure accuracy I will make up one large batch of each molar for each test, as opposed to making up the molar each time I use it.
Apparatus
1 x clam stand and boss
1 x small container for chips
1 x gas syringe
1 x conical flask
1 x delivery tube and bung
1 x stopwatch
1 x measuring cylinder
1 x pipette
2 x small glass beaker
1 x electronic balance
150g marble chips
batch of 3M hydrochloric acid
Method
- Place the gas syringe in the clamp.
- Place the small container that you have for the chips on the balance, wait for the display on the balance to stop moving, and then press the ‘tare’ button.
- Weigh out 10g of marble chips as accurately as possible.
- Place the measured out chips in the conical flask.
- Measure out 10cm³ of 3 molar hydrochloric acid as accurately as possible using the measuring cylinder.
- Attach the delivery tube on the syringe, test and adjust the syringe’s height on the clamp so that you can easily attach the bung to the conical flask.
- Make sure that the plunger in the syringe is pushed in.
- Pour the acid into the conical flask containing the chips and QUICKLY place the bung on the flask.
- Another member in the group should start the stopwatch as soon as the bung is placed on the flask.
- Wait until the gas has pushed out the syringe to the 100cm³ mark and then stop the stopwatch
- Care must be taken so that the bung is removed after the test has stopped otherwise pressure will build up.
- Also care must be taken so that the plunger does not come out of the end of the syringe, as the equipment is expensive.
- Record the results in a results table.
- Repeat the test three times so that a good average is achieved, if you want to, you may repeat the test more times to get a better average.
Making different molars
To make different molars the following formulae should be used:
2.5 molar – 25cm³ HCL + 5cm³ H20
2 molar – 20cm³ HCL + 10cm³ H20
1.5 molar – 15cm³ HCL + 15cm³ H20
1 molar – 10cm³ HCL + 20cm³ H20
Diagram
Results table
Conclusion
My predictions that I made were correct, and are supported by my results and graph. The graph is significant indication in the relation between affecting the molar of acid.
The line of best fit shows that there is a dramatic drop between the time it takes for the acid to react with the marble chips on the 1 and 1.5 molar, but then the decrease slows down and becomes more gradual.
Evaluation
If I had more time I would like to of made more tests to improve the average, also I would of liked to of tested a wider range of molars to see if the decrease in reaction time is more or less dramatic with higher molars.
I thought we conducted the experiment very well and efficiently, however, we did have some anomalous results in several of the molars, this may have been down to a number of variables as described earlier in the exploration; such as concentration of the acid. We ignored these results and repeated the test when we came across them, with this the anomalous result did not appear again.
