An experiment to investigate the rate of reaction between

From my results I have come to the conclusion that they do support my prediction. However I can see that I need to become more accurate when straining the marble chips to get rid of the acid.

I have decided that I will change the concentration of hydrochloric acid that reacts with the marble chips. I will also look out for a change in mass of the marble chips which I will do by weighing them before and after the reaction. The concentrations I have chosen to use in my experiment are:

• 2.0
• 1.6
• 1.2
• 0.8
• 0.4

I have decided that during my experiment I will keep the following the same:

• the temperature
• the surface area of the marble chips
• a catalyst not being present.

Apparatus

• 150cm³ of hydrochloric acid
• 25g of marble chips
• 100cm³ of distilled water
• Measuring scales
• 5 conical flasks
• 5 paper towels
• 50cm³ measuring cylinder
• Stop clock
• A sieve
• Safety Glasses

A diagram of the set up is shown below:

Method

Before I begin to set up my experiment, I will make sure all hair is tied back, and put on safety glasses. Once this is done I will begin to measure out however much distilled water is needed, and then the concentration of hydrochloric acid. To make sure that concentrations are not mixed up I will label each one. I will then get some measuring scales and weigh out as close to 5 grams as possible of marble chips. I will repeat the above steps 5 times for every concentration. I will then take the first solution and add the 5 grams of marble chips, and press start on the stop clock. After 25 seconds I will pour the solution through a sieve, making sure only the marble chips are remaining. I will then get some paper towels and dry off the marble chips. I will then re-weigh the marble chips and record the results. I will repeat this method for the other concentrations. I will also repeat each concentration if any of my results seem irregular.

Results

• Experiment 1

• Experiment 2

• Average results

Analysis

From my graph I can see that as the concentration of hydrochloric acid increased as did the rate of reaction. This is because when the particles reacted they collided with enough energy to make them react. As the concentration of acid increased, the number of particles increased, and so there were more particles in contact with the marble chips. This led to more collisions taking place and so the rate of reaction increased. The graph shows that as the concentration increased, the number of collisions also increased, increasing the rate of reaction in direct proportion.

I feel my results do partly agree with my original prediction. In my prediction I said that doubling the concentration will double the number of particles and also double the number of collisions, therefore doubling the rate of reaction in direct proportion. Although they do not exactly double they are extremely close. For example at 0.2 molar the rate of reaction was 0.375, and at 0.8 molar the rate of reaction was 0.6 molar. This shows that doubling the rate of reaction at 0.2 molar is very close to the value at 0.8 molar. The reasons for my results not supporting my prediction 100% is most probably due to sources of error within my experiment.

Evaluation

From my graph I can see that I have two anomalous results which were at 2.0 molar and 1.2 molar. These anomalies are most likely to have occurred due to sources of error within my experiment.

Sources of error I came across during my experiment included:

• Surface area of the marble chips. There was no way I could control the surface area of the marble chips. So in some of my solutions, some of the marble chips would have had a greater surface area and so would have had greater contact with the solution, meaning the rate of reaction would be greater. If I were to repeat my experiment I would make the marble chips into a powder, so that they had the same surface area.

• Measuring the solutions. It was very difficult to get the meniscus to sit in the correct place. If I were to repeat my experiment I would consider using a burette as it is more reliable.

• Difficult to coordinate between adding marble chips to the solution and starting the stop clock. If I were to repeat my experiment I would use the help of another person.

If I were to repeat my experiment I would also think about completing more repeats, as I only did so once the first time I completed the experiment. My results were consistent but feel with more repeats they could have been even more consistent and also more reliable. I would also use a larger number of different concentrations, and so I would be left with a more reliable and accurate conclusion.

An alternative experiment I could have done was to test one of the other variables I stated earlier in this write up. I may then be in a better position to draw a more detailed conclusion. So, for example, I could investigate the surface area of marble chips and how it affects the rate. If I were to complete this experiment I would separate the chips using their size of their surface area. I would then go on to weigh out equal amounts of the chips using their different sizes. Then I would measure out the same 5 solutions of hydrochloric acid, using the same concentration. I would then add the smallest chips to the first solution, time them for 20 seconds, and then sieve them. I would then precede on to dry them with a paper towel, and then weigh them. I would repeat this method for the different sizes of marble chips.

I do however find that my results are sufficient enough to draw a firm conclusion because my results were consistent as I did use a repeat. However I do have anomalies and sources of error within my experiment. If I were to repeat my experiment using the improvements I have already explained above, I feel my conclusion would be much more reliable.