- Concentration of hydrochloric acid- this is the proportion of hydrochloric acid in the solution.
- Volume of acid- this will be the amount of hydrochloric acid that will be reacted with the marble chips.
- Catalysts- by weakening bonds these increase the rate of reaction by lowering activation energy a catalyst will not be used in this reaction, however.
- Mass of marble chips- The mass of the marble chips is a way of measuring the quantity of chips being used.
- Temperature- the temperature adds energy to the reaction an affects how quickly the particles move. By doing this temperature affects the number of affective collisions
Fair Test
To ensure that a fair test is carried out is one of the most important things in any experiment.
Otherwise the results that would be obtained would be useless and inaccurate, which could then lead to critical errors in the analysis and conclusions. Only one variable should be changed which in this case is the concentration, for reasons see above.
In this experiment I will be using a number of controlled variables or fixed variables to certify that the experiment is fair, and that only one variable will be changed. These controlled variables have been listed below:
- Firstly, and possibly one of the most important the volume of hydrochloric acid, should be measured carefully and accurately. Inaccurate results will be produced if this is not considered carefully. To try and overcome this problem we have used the method called titration to accurately measure the volume of hydrochloric acid. This will hopefully lower the margin for error.
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A gas syringe should be used, and be fully pushed to 0.00cm³ before starting the experiment.
- It has to be made sure that the marble chips do not touch the acid before measuring and timing so that precise readings are recorded.
- The same acid will be used- Hydrochloric acid throughout the course of the experiment.
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The same volume of acid will be used- 25cm³; it will be measured to the nearest millimetre cubed. I have chosen to use 25 cm3 because I had previously used it in my preliminary experiment. 25 cm3 of the acid was sufficient to obtain accurate results.
- The same apparatus will be used, if any of the equipment is faulty, the results will be more accurate than using different equipment with dissimilar faults.
- The size of the chips have to be kept similar, i.e. medium chips will be used, the surface-area, however, may differ. As stated above, it is impractical to keep the surface-area of the marble chips equal, as it is not quantitative. I used medium sized chips because in the preliminary experiment large chips were too slow in reacting and the small/powdered chips were too fast in reacting, therefore there would be a large margin of error whilst measuring the gas produced.
- The experiment will be kept in the surroundings where the temperature is constant and alike. Once each experiment has finished, I will ensure that I pause the stop watch immediately.
To make certain that the results I produce will be both reliable and precise; the experiment will be repeated twice. Averages will then be calculated.
Risk assessment
Safety is an important factor in any experiment.
- Hydrochloric acid is irritant and if used incorrectly can cause accidents.
- Goggles and overall will be worn throughout the experiments.
- Once an experiment is completed, good care should be taken to release the bung from the conical flask, more importantly, pour the remaining acid into an appropriate place.
Preliminary Experiment-
Apparatus used:
-Hydrochloric Acid (25cm³)
-Small marble chips (approximately 1.00g- nearest 0.01g)
-Electronic scales
-Conical Flask
-Gas syringe
-Bung
-A stop Watch
-Plastic boat (carry marble chips)
-Clamp and Bolt
-Measuring Cylinder
-Beaker
-Bench mat
Method
To carry out the experiment we used a gas syringe and timed how long it took for the syringe to be filled. The volume of the syringe was one hundred cm³. We reacted both of the reagents in a conical flask and measured the mass of the chips on a electronic balance to get a fairly accurate reading.
Why did we carry out the preliminary experiment?
This preliminary experiment was carried out to find the mass of chips to use, and this experiment was also used to test the range of concentration to use in the experiment. These experiments were important to carry out because we could make sure the reaction did not fill up the cylinder too quickly leaving many times blank as the cylinder cannot contain all of the gas. This could also make sure the reaction did not take place too slowly to give us a small range of results.
Conc
We have chosen to use medium sized calcium carbonate chips because we already know from our chemistry knowledge that by using small calcium carbonate chips the reaction would be very fast, and in some cases, small chips in 2.00 M concentrations of Hydrochloric acid would pose a problem because the reaction would be very quick, and probably too quick to record. This is because a small calcium carbonate chip has a large surface area and this would increase the rate of reaction. We also know that by using large chips the rate of reaction would be very slow because it has a small surface area, and in some cases the reaction rate would be very slow, (large chips in 1.00 M concentration of Hydrochloric acid.) Subsequently, we chose the middle one and we decided to use medium sized chips, and below are the results with a graph which puts the results into perspective.
TABLE OF RESULTS FOR THE PRELIMINARY EXPERIMENT.
Experimental prediction
I predict that the higher the concentration of Hydrochloric acid, the quicker the reaction will take place. This is because in a higher concentration there will more hydrochloric acid (HCl) molecules in the volume. This simply means that there will be a greater possibility of the calcium carbonate (CaCO3) molecules colliding with the hydrochloric acid and reacting. Reaction rates are
explained by the collision theory which states that a rate of reaction depends on how hard and how often the reacting particles collide with each other. Particles have to collide hard enough to react.
The amount of surface area exposed also affects the speed of the reaction as the larger the area of limestone exposed, the more the particles will have to move, therefore collide, and in turn increasing the number of collisions and the quicker it will weather away.
The rate of reaction, nevertheless, should decrease as the experiment develops because as the time for the reaction increases, the amount of hydrochloric acid (HCl) molecules present will decrease as they have been reacted to form water calcium chloride (CaCl2) and carbon dioxide (CO2). The excess water and calcium chloride visible as the experiment advances should reduce the rate of reaction because of the decrease in concentration. Therefore when a graph is plotted, a curve will appear as the rate of the reaction at the beginning of the experiment will fast, and gradually will slow down. This is because there are fewer particles with the required activation energy (Ea). This means there are fewer
particles to collide with one another, slowing down the reaction. I also predict that the increase in the concentration of acid will be directly proportional to the increase of the reaction rate.
I.e. Concentration of acid α Increase in reaction rate.
This is because when there are more hydrochloric acid molecules present, there would be more of a chance that a collision will take place. Therefore the probability of the particles colliding would double.
Method for the REAL EXPERIMENT.
- Firstly, we set up the experiment using the above apparatus as shown below.
- Before we start the experiment, we will draw out a simple table in which we will then record the results on.
- We will pour 25cm³ of 2M hydrochloric acid, using the method of titration, and we will measure out the amounts of 1.00 M, 1.25 M, 1.50 M, and 1.75 M into a conical flask.
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We will get the stop watch ready and place the small marble chips into the conical flask and put the bung on top to trap the CO2, and immediately we will start the stop watch.
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Every 10 seconds, we will record the mass of marble chips and note them down. As we knew the masses of marble chips, we will be able to in turn work out the mass of CO2 lost.
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We will carry out this procedure until the time had reached 100 cm3 of CO2.
- Once the experiment will be complete we will switch off the stop watch, release the bung from the conical flask and pour the remaining excess hydrochloric acid into a round basin.
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We will then plot a graph of our results, with the Time (seconds) on the x axis and loss in mass of CO2 on the y axis.
- This procedure will be repeated again for all the concentrations of hydrochloric acid.
