Rates of Reaction between Calcium Carbonate and Hydrochloric Acid.

David Shuker DNE – A1

Rates of Reaction between Calcium Carbonate and Hydrochloric Acid

Aim: To investigate the rate of reaction between calcium carbonate and hydrochloric acid. To do this I must change a variable to see what effect it has on the speed of the reaction. Possible variables include: the size (surface area) of the marble chips (calcium carbonate), the amount of marble chips, the amount of hydrochloric acid, the pH of the hydrochloric acid, the concentration of the hydrochloric acid, and the temperature of the acid. In my experiment I have chosen only to change the temperature of the acid.

Equations: The word and symbol equations for the reaction between the calcium carbonate and hydrochloric acid are:

calcium carbonate + hydrochloric acid ⇒ calcium chloride + water + carbon dioxide

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

Prediction: I can predict that my results will show positive correlation between the rate of reaction and temperature of the acid, so that as the temperature is increased, the rate of reaction shall also increase. This is because that for a reaction to occur particles must collide with sufficient energy (speed) to break the bonds within the reactant molecules and also form new bonds to produce the product. The higher the temperature of the acid, the more energy the particles will have, increasing the chances of a successful collision and allowing the bonds to be broken down and reformed more easily.

I also predict that the rate of reaction will not stay the same throughout the duration of each experiment, and will be greatest at the start and will decrease as the reaction proceeds – this is because that all the while the reaction is taking place, particles will continue being used up during successful collisions, slowing down the reaction simply because there are less things to react with. As the experiment continues the acid shall also begin to cool down, meaning that the particles will become less energetic making a successful collision less likely to take place. Because of this, I predict that when I draw a graph of my experiment, the line of best fit will show a levelling off as time passes as the reaction slows down and the reactants are used up.

Planning:

Safety: In order to keep my experiment safe, I shall wear goggles to insure that my eyes are not damaged if any of the acid is splashed or spilt. I must be responsible when handling the acid and water bath to prevent spillage.

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Planning:

Fair Testing: In order to gain accurate results, I must conduct the experiment in as fairer way as possible. To do this, I must keep all the variables the same, except for the one I wish to change, the temperature of the acid. For example, I must have marble chips of the same size, because if they weren’t they would have smaller or larger surface areas for the acid to react with, resulting in the speed of the reaction being faster or slower than it should be. I must also not reuse the marble chips or acid in any of my experiments, as some of the reactants would already have been used up resulting in less gas being produced and more slowly.

When I use different temperatures of acid, I must make sure that they are all accurate and of the temperature I need. When I am reading the measurements on the measuring cylinder I must be accurate in doing so, so that the results are correct.

I will also repeat each experiment 3 times so that I can take an average and spot any anomalous results, making my readings as accurate as possible.

Apparatus:

Hydrochloric acid – A reactant
Marble chips (calcium carbonate) – A reactant
Thermometer – To monitor the temperature of the acid
Conical flask – For the reaction to take place in
Water bath – To heat up the acid with
10ml Measuring cylinder – For measuring the amount of acid
50ml Measuring cylinder – To measure the amount of gas produced
Bung with a tube – To transport the gas made in the reaction to the 50ml measuring cylinder
Tub of water – To store the 50 ml measuring cylinder in
Stop watch – To time the reaction

Method: I plan to use a range of temperatures from 16°C to 56°C, increasing by 10°C each time. I am using this range of temperatures because it includes 26°C which is room temperature, and I believe that this would be the most relevant result, and would also save time because I wouldn’t have to heat/cool the acid to a certain temperature, as it would already be at room temperature.

Firstly I shall put the 50ml measuring cylinder into the tub of water upside down, filling it with water in the process. Then I will put the tube attached to the bung in it. Then I will measure out roughly 1 gram of marble chips, and put them into the conical flask. I will then measure out 10ml of hydrochloric acid using the 10ml measuring cylinder and then heat it to the appropriate temperature using the water bath (or in the case of 16°C, cool it down in a fridge). I will then add the acid to the conical flask with the marble chips and immediately put the bung in it and start the timer.

I shall then begin to take measurements every 30 seconds of how far the water level of the measuring cylinder has gone down. By doing this I will know how much gas has been produced from the reaction, because when it is produced it goes through the tube into the measuring cylinder, rises up through the water to the top and pushes the water downwards.

My Results:

*I have chosen to ignore this result for my averages as it is clearly anomalous

To make my results as accurate and easy to understand as possible, I have decided to draw a table and graph showing only my average results, allowing me to compare them and make conclusions.

Analysis: At their most basic level, my results show that the higher the temperature of the acid, the faster the rate of the reaction will be. As I stated in my prediction, this is because when the acid is hotter the particles are more energetic, making it easier for them to break down the bonds within the reactant molecules and form new bonds to make the product.

My other prediction was that as each reaction goes on, the rate of the reaction should begin to slow. However, in my graph all the lines of best fit seem to be relatively straight and did not seem to level off or show signs of much curvature as time went on as I had expected. However, I do not think my prediction is wrong – I believe that if I had allowed my experiment to go on longer and measured the rate of reaction for more than just 120 seconds, the graph would show that the reaction would indeed begin to slow until all possible collisions had taken place. As stated in my prediction, I believe this would happen because as the experiment went on, more of the reactants would be used up during successful collisions, resulting in the reaction slowing down simply because there would be less particles to react with.

Evaluation: Although the results of my experiment have proved conclusively that the hotter the acid, the faster the reaction will be, they are not firm enough evidence to show by exactly what amount. This is because my results seem to indicate that they are at least slightly inaccurate, because although there are few obviously anomalous results, the amount of gas produced still varies by several millimetres, indicating that many more results should have been taken and that the experiment could have been performed much more accurately.

For example, the weight and size of the marble chips were not measured accurately, and were only made sure to weigh roughly 1 gram. To make this experiment more accurate I would have to spend much more time making sure all the marble chips were of exactly the same size and weight.

Also, as I said in my analysis, I would allow my experiment to continue for longer until all possible reactions had taken place, so that I would be able to measure how the rate of reaction changes as more of the reactants are used up. To do this, I would have to use a much bigger measuring cylinder that could hold all the gas produced in the reaction without all of the water being pushed out. In fact, instead of using a measuring cylinder I could use a syringe as it would be easier and more accurate to read off.