To find out and analyse what factors affect the rate of reaction between limestone and acid rain.

Preliminary Experiment

For my preliminary experiment, I reacted some hydrochloric acid (with a concentration of 2 moles) with several medium sized marble chips (calcium carbonate), and collected the amount of gas produced.

This table shows the results of my preliminary experiment:

This shows that in between 0 and 300 seconds (5 minutes), carbon dioxide gas was collected in the gas syringe. This totalled up to 97 ml after the 5 minutes was over. I can use this method of measuring rate of reaction in my main experiment.

I have also plotted a graph from my preliminary results:

From this graph, you can see that there is a positive correlation, and that as the amount of time increased, so did the amount of carbon dioxide gas collected. In my main experiment, I will compare graphs for all the concentrations, and comment on any similarities or differences between them.

My preliminary experiment helped me a lot when deciding values for my real experiment. From my preliminary work, I decided that the best amount of acid to use would be 100cm and a good mass of medium sized marble chips to use was 1 gram. I also decided from my preliminary experiment that the best interval to record the volume of gas in my experiment is every 30 seconds. I found that the concentration of 2 moles reacted quickly and after 5 minutes the gas syringe was almost completely filled with gas. Due to this, I decided from my preliminary experiment that 2 moles would be the highest concentration of acid I would use, because anything higher would fill the gas syringe before the time period of 5 minutes. This means that in my main experiment, all my concentrations will be lower than 2 moles. I am going to use the same time period (of 5 minutes [300 seconds] total, every 30 seconds gas collecting), in my main experiment too.

 

Prediction

The collision theory states that all substances are made from particles, of which may be atoms, molecules or ions. Before there is a chemical reaction, these particles must crash together – they must collide.

The more collisions between particles in a certain amount of time; the faster the reaction.

My prediction is that the higher the concentration of acid, the higher the rate of reaction. I think this because in a more concentrated solution there are more particles to react, so therefore it is likely that there will be more collisions and the ‘collision frequency’ will be higher. As I stated earlier, the collision theory says that the more collisions between particles the faster the reaction will be. This is what my prediction is based on. If I do an experiment when the acid has a concentration of 1 mole, and then another experiment with the acid concentration of 2 moles, it is likely that the reaction speed will be twice as fast, as I have doubled the concentration of the solution.

Apparatus

I have chosen to use a gas syringe as part of my apparatus to measure the amount of carbon dioxide gas given off. I could have used scales instead to measure the change in mass (of the chips) during the reaction, however I have decided that using a gas syringe will produce more accurate results and measuring the amount of carbon dioxide gas produced is a very effective way of measuring the rate of reaction.

I will clamp the gas syringe to a stand, and have a flask containing my solution (of a specific concentration). I will then connect the flask to the gas syringe, drop my 1 gram of medium sized marble chips into the solution and start the timer. I will use the gas syringe to record the amount of carbon dioxide gas produced at a regular interval of every 30 seconds. I will record all of my results in a table. I will repeat this method for each of the six concentrations.

Method

When I am doing my experiment, I am going to use calcium carbonate to represent limestone and hydrochloric acid as acid rain.

I am going to use the following concentrations (of acid) in my experiment: 2 moles, 1.8 moles, 1.6 moles, 1.4 moles, 1.2 moles and 1 mole.

I am investigating six different concentrations so I will have to run my experiment six times for each concentration individually. To work out the amount of acid and water I needed for each concentration, I used this formula (for a total of 100ml):

                                  1000 x Concentration (m)

Volume of Acid =         -----------------------------

                                            2x10        

This table shows the results of my calculations and the amount of water and acid I will use for each concentration:

        

        

Having changed the independent variable (concentration of acid), I will be measuring the amount of carbon dioxide gas given off (cm) every 30 seconds. From this information, I will be able to plot graphs and find the rate of reaction. I can do this by dividing the amount of gas produced by the amount of time it was produced in.