An Investigation into the Factors Affecting the Rate of the Reaction Between Calcium Carbonate and Hydrochloric Acid

An Investigation into the Factors Affecting the Rate of the Reaction between Calcium Carbonate and Hydrochloric Acid

A chemical reaction is the process by which atoms or groups of atoms are redistributed, resulting in a change in the molecular composition of substances. The reaction rate is how quickly a reaction occurs and this can be affected by four different factors:

ÐŽ¤ changing the surface area of any solids involved

ÐŽ¤ changing the concentration of reactants in solution

ÐŽ¤ changing the temperature at which it is carried out

ÐŽ¤ the use of a catalyst

I am going to investigate into exactly how one of these variables affects the reaction rate and I believe the most suitable variable to change is the concentration of the solution as all necessary equipment is available within the school chemistry lab, and five results can be obtained easily and within the time allowance.

I will be using the following reaction in my investigation:

Calcium carbonate + Hydrochloric acid Calcium chloride + Carbon dioxide + Water

CaCO3 (s) + 2HCl (aq) CaCl2 (aq) + CO2 (g) + H2O (l)

I have chosen to use these substances because research has shown that they react well together. This will mean that I will be able to have quick and efficient experiments.

Aim: I wish to test how the concentration of the hydrochloric acid affects the rate of a reaction

In order to fulfil this aim I have to come up with a suitable method that will produce reliable data so that a valid and accurate conclusion can be drawn. Carbon dioxide seems an obvious product from the reaction to use to calculate the rate, as it is common scientific knowledge that the faster the reaction, the more carbon dioxide should be produced. The test for the presence of carbon dioxide is that it turns transparent limewater cloudy and I could use this idea to base my experiment on.

Previously we have studied the effect of changing the concentration of a solution on the reaction rate between sodium thiosulphate (Na2S203) and dilute hydrochloric acid (HCl), where we placed the reaction vessel over a pencilled cross drawn on a piece of paper. We then timed how long it took before we could no longer see the cross as the reaction had caused the mixture to turn cloudy. I believe this method could be adapted for my experiment; however I would have to use two conical flasks; one where the reaction would take place, and one containing the limewater with a delivery tube connecting the two. Bungs in the conical flasks will prevent the carbon dioxide escaping.

It is essential that all other independent variables except the concentration of the solution remain constant throughout the investigation so that the experiment is fair and an accurate conclusion can be drawn. If more than one independent variable is changed at a time, it is impossible to work out which one is causing the change in the reaction rate. Therefore the size of the calcium carbonate, amount of hydrochloric acid and the temperature at which the investigation shall be carried out at shall be kept constant throughout my experiment.

I have decided to use 50ml of acid but it should give me a relatively quick reaction, so the experiment will take only a short amount of time. For the same reason I shall use 10ml of limewater so it does not take very long to turn cloudy. The experiment will be carried out at room temperature which is approximately 20ўЄC and I shall use small marble chips of 2-5ml.

I shall test 5 different concentrations of hydrochloric acid and these are 0.5 molar, 1 molar, 2 molar, 3 molar and 4 molar. To enable me to gain reliable results, I shall test each concentration three times and then take an average of these results to plot on a graph. This should hopefully give me a clear result of what effect the concentration of acid has on the reaction rate.

Before my main experiment I will perform a trial experiment to make sure I can complete the experiment in time and make sure I am using appropriate quantities of each substance. To make my results accurate and reliable, I hope that each experiment will last over thirty seconds, and if this is not the case in my trial experiment, I will alter the quantities.

In order to make my experiment safe I will wear goggles and an overall when I handle the acid as it is corrosive and if any came in contact with my skin during the experiment I would wash it off immediately. As I described above, my experiments will be fair as it will be performed under the same conditions, with hopefully only the concentration of acid being altered for each experiment.

The equipment should be set up as shown in the diagram below:

The small marble chip will be placed in the conical flask first and then the hydrochloric acid will be poured into the flask and as soon as all the acid is in I will start the stop clock and put the bung on the flask. I will then watch the pencilled cross from and above and stop the clock at the exact moment that I can no longer see the circle. I will record this time in my results table and then set up the experiment for the next measurement.

Modifications following preliminary experiment

For my trial experiment, I placed one small marble chip in 50cm©Ñˆ of 1 molar hydrochloric acid and timed how long it took before a pencilled cross was no longer visible under a conical flask containing 10cm©Ñˆ of limewater. Although the limewater began to turn cloudy eventually, it took more than 10 minutes to do so and I believe there were a few reasons for this. Firstly there was not enough limewater in the conical flask, as the delivery tube did not reach it and this would have caused the carbon dioxide to be given off into the air inside the conical flask rather than into the limewater. Also, the reaction was not violent enough, and I feel more marble chips were needed to speed up the reaction to ensure that I will be able to complete all 15 experiments in the given time allowance.

Therefore, I am going to increase the amount of limewater I use from 10cm©Ñˆ to 70cm©Ñˆ as this is the amount required for the end of the delivery tube to be under the limewater. Also, I am going to use 20 grams of marble chips for each experiment rather