Particle size
The reaction between calcium carbonate and dilute hydrochloric acid is used to prepare CO2. Varying the size of the Calcium Carbonate can make the reaction produce more or less Carbon Dioxide in the time frame available. I could try using either lumps or powder and see which reaction would produce more gas. This would have to be kept the same to ensure that the surface area of the Solid reactant remains the same as a greater surface area produces more gas than a smaller one. I have decided to use marble chips as tests reveal that powder allows to much gas to be produced to obtain an accurate recording.
Concentration
Concentration is a very important factor in rates of reaction. The concentration of a solution can greatly effect a reaction this is because there will be more particles of the reactant to react with, which will increase the time taken for the reaction. If the concentration of an acid is increased, the rate of reaction will increase because the collision rate would be higher and the amount of CO2 would be given out more quickly. This is why the concentration of the acid must remain the same for the entire experiment. I have decided to use 2 molar acid for the experiment, as it id strong enough for the reaction to occur with decent speed without going to fast. It is also the most powerful acid available for class use. I decided to use this strength of acid due to the results from earlier tests, of which the results are shown below.
Temperature
The higher the temperature the more energy each particle will have which means it will vibrate more, causing the amount of collisions to increase. As the particles collide more than usual at a high temperature then it will have a high chance of reacting, this will increase the rate of reaction. To alter the temperature, as the main variable would be impossibly hard to keep constant, making it useless for that however it is still important that the temperature remains the same.
Time
A fixed time would have to be decided when the amount of gas produced from the reactants is recorded. This is the reading that shall be used to find out if my earlier prediction is correct. During the Testing Phase, I conducted some basic experiments looking at time possible for use and I have decided on using 1min 30secs as my record time. The results from the tests are shown below.
Amount of solid reactant
Keeping the amount of Solid Reactant is important as a greater amount represents a larger surface area for the reaction to occur. This would results in greater amount of the gas being produced. During earlier tests I decided on 1.5g of Marble Chips to be used as this produced enough gas to be accurately measured whilst also ensuring the amount of gas produced in relation to the variable is noticeable. The results from the test are shown below.
Amount of reactant solution
The amount of acid used in the reaction is important is that a greater amount of acid would have more Molecules to react with the Solid reactant. This would result in a greater amount of gas being given of. So during the experiment the same amount of reactant solution must be added to the solid reactant to ensure a fair test. I have decided on 50cm3 of solution to be used, this is due to two reasons. First 50cm3 is a good round number with which to dilute the acid from, replaced 10cm3 of acid each time with 10cm3 of water. Also 50cm3 is a good amount of solution that ensures a reaction will take place and provide noticeable and easily readable results.
Equipment
Gas Syringe
Conical flask
Marble chips (CaCO3)
Acid (HCl) (2 Molar)
Glass Pipete
50ml Measuring Tube
Clock
Clamp
Pole
Cork
Rubber Tube
Electric Scales
Glass Beaker
Method
First, I prepared the apparatus above, I found that the apparatus is good enough to carry out the experiment and get reliable results. First, I will use the top man balance to weigh out 1.5g of CaCO3, which is in marble chip form. Make sure the apparatus is safe and then you will be able to measure out 50ml of acid. This is done using the glass pipette measuring out two quantities of 25ml and then poured into the conical flask. Also, after measuring the CaCO3 you would be able add that to the conical flask. To keep the experiment fair you need to always place the acid first then the Calcium Carbonate or the opposite, this must be done all the time. As you add both reactants to a conical flask, you must immediately place the cork onto the flask. There is also the syringe were the gas is collected and connected to a glass tube and the cork, the gas collected would be CO2. The syringe is help in place on a stand and clamp to stop it rolling around and let the stopper easily come out of the syringe.
Once I have repeated this process twice, I shall repeat again however diluting the acid with water. This is done by measuring out 50ml of acid and pouring it into the measuring tube. 10ml is then poured away and 10ml of water added to bring the total back to 50ml. The experiment is then repeated using the quantities of 30ml acid/20ml water, 20ml acid/30ml water, and 10ml acid/40ml water.
I will not use 0cm3 of acid with 10cm3 of water because there will be no reaction. To keep the experiment fair I kept the temperature of the solution constant at room temperature as well as the particle size of the Calcium Carbonate. You also had to make sure that the amount of CaCO3 must be kept constant so I used 1.5g. In addition, I used a clock to measure the time taken from as soon as the reactants are put together to time one and a half minutes before writing down the result.
All results are to be repeated at least twice to ensure that anomalous results are discovered, and alternative figures are available for use.
Key Variable is Concentration of Acid
Control Variables are;
- Temperature
- Concentration of Acid
- Chip Size
- Solution Amount
- Time
- Amount of Solid
Safety
Safety is an important factor when dealing with acids and so I will follow these precautions at all times.
- Wear full safety goggles, not glasses, as they do not provide side on protection at all times.
- Wash hands after dealing with any chemicals, I don’t wish to end up with acid in my mouth
- All equipment must be washed up thoroughly after use to ensure acid is not accidentally passed onto someone else.
Results
Below are the results from my experiment.
Analysis
The results above have provided clear and accurate readings that I can now process as useful data. First, in the graph we can clearly see a pattern has emerged. The graph shows a Strong Negative Correlation from the results. This means that the amount of gas produced increases in proportion with the strength of the acid. I believe this is because as the solution of acid and water became weaker the acid molecules were spread out more. These meant that these molecules could no longer easily reach the Calcium Carbonate, so reducing the amount of gas produced.
These two diagrams above show the effects of dilution. The first diagram shows a concentrated solution that has many Acid Molecules that can easily get to the Calcium Carbonate Chips to react with them. Diagram two shows a diluted solution that has many water molecules but few acid molecules that cannot easily reach the Calcium Carbonate so little gas is produced.
Using the graph I can easily predict results within the graph. The correlation of the results being so strong, there is a high chance of this prediction being correct. Outside the graph, results could also be predicted. A stronger Acid would see a rise in the amount of gas produced, however further experiments would have to be conducted to back this up. I feel that the ratio at some point would level of as the reaction would reach critical point, allowing no further amounts of reaction to take place.
The percentage error of the results indicates a low chance of error in the results, which indicates that an accurate and fair experiment was performed to the best standards with the facilities available.
This data reflects well on my prediction, which was that with an increase of Concentration, I would see an increase in the amount of gas produced. The graph above clearly shows that this is true and not only that but proves that the decrease is exponential meaning that it decreases in a relative amount to the concentration of the acid.
Evaluation
My conclusion is that the experiment was successful and that the results were reliable to make a conclusion from, we also find that the results were like my prediction and like the preliminary test. I also will conclude that concentration of the acid does effect the rate of reaction.
The accuracy on this experiment I feel was exceptionally good. The percentage error rates where low and the graph correlation of the results was near to perfect. I feel with more repeats the correlation would become ever more streamlined and accurate. No anomalous results were found or incorporated into the experiment that can be clearly identified, also adding to the accuracy of the experiment.
There were a couple of points for the experiment to be improved by, first that by adding the CaCO3 and quickly placing the cork on top will lose time and some of the immediate product is lost. Also that a normal person pressing the time is not the most accurate of techniques. This obviously increases the error percentage in the results making the result outcome slightly incorrect. One way to improve the experiment would be to use a cork with two holes fitted with valves. One to enter the acid and CaCO3 powder and one connected to the syringe for the product of the reactants to be let out. In my view, I find this a more reliable technique.
In addition, from the graphs I concluded that after the reaction reaches a peak it slowly comes to a complete halt. This meant that the graph was accelerating at first and then the gradient changed for the curve to become towards a vertical line. Although not indicated on the above graph nor supported by any of the evidence presented in this Investigation I feel that this would be a valuable extension of the product to discover when and where this curving begins and to what extend it occurs.