I will use marble chips and different concentrations of hydrochloric acid and water to see how it affects the rate of reaction. I will use concentrations of 50cm3 using different volumes of water and acid.
I am investigating how the rate of reaction between marble chips and hydrochloric acid is altered when the concentration is changed. This is the word equation for my investigation,
Calcium + Hydrochloric Calcium + Carbon + Water
[IMAGE]Carbonate Acid Chloride Dioxide
The symbol equation for my investigation is,
[IMAGE]CaCo3 + 2HCL CaCL2 + CO2+ H2O
I predict that when I have a higher concentration I will have a faster rate of reaction. Referring to Edexcel Science Revision Guide edited by Mary James, the collision theory states that when there are more particles, there are more collisions making the reaction faster (see diagram). Also referring to Chemistry For You by Laurie Ryan, it states As you increase the concentration of the acid, there are more acid particles in the same volume. Therefore there is a greater chance of acid particles colliding, and reacting with more particles on the surface of the marble. So, this means that the higher the concentration of my acid the faster the reaction.
I will weigh out one gram of marble chips using a balance and put it in a conical flask and add to it a concentration of 50cm3 using water and hydrochloric acid. I shall start by filling up a measuring cylinder with water and putting it in a water bath so I can record how much gas has been given off. I shall then put my one gram of marble chips measured using in a conical flask then add to that my concentration of hydrochloric acid and water, put on the bung and start the stop clock. I shall record how long it takes for 25cm3 of gas to be collected.
The reason I chose to do this investigation was because I have previously done it so I know what kind of results to expect. Also the experiment I shall I do was done in Chemistry For You by Laurie Ryan and so using the evidence I collected from these experiments I know what type of results to anticipate. I shall use a small range of readings but shall repeat each concentration three times then find the average and rate of reaction. The readings I shall use will be:
· 10cm3 of hydrochloric acid and 40cm3 of water
· 20cm3 of hydrochloric acid and 30cm3 of water
· 30cm3 of hydrochloric acid and 20cm3 of water
· 40cm3 of hydrochloric acid and 10cm3 of water and
· 50cm3 of just hydrochloric acid.
I shall use quite a lot of apparatus for this experiment, I shall need:
· A Stop Clock To determine how long it takes to collect 25cm3 of gas to be given off.
· A Water Bath To stop the water escaping from the measuring cylinder.
· A Measuring Cylinder To measure the amount of gas that is given off.
· A Conical Flask Contains the marble chips, hydrochloric acid and the water that will make the reaction.
· A Tube To connect the conical flask to the measuring cylinder.
· A Stand To hold up the measuring cylinder.
The variables that I shall be changing will be the concentration of hydrochloric acid and water. I shall change them so that added together the make a 50cm3 solution. I shall use the following readings:
o 10cm of acid and 40cm of water. (least concentrated)
o 20cm of acid and 30cm of water.
o 30cm of acid and 20cm of water.
o 40cm of acid and 10cm of water.
o 50cm of acid and no water. (most concentrated)
I shall keep the mass of marble chips the same (one gram) so that no reading will have an unfair advantage over another. I must also use the same type of marble chips, I shall use big chips. I must make sure I use these for all my readings as if I used powder for one then that reading will have more of a surface area to react upon making the reaction faster. I shall also use the same molar of acid, I shall use two molar as if I changed this my reaction would be slower.
Concentration of acid/cm3
Concentration of water/cm3
Time Taken for 25cm3 of gas to be given off/mins
1 2 3
Rate of Reaction/s
Looking at both of my graph I can make the conclusion that as the concentration increases the reaction gets faster. This is because when there is a higher concentration there are more particles present. The more particles present, the bigger the chance of a collision making the reaction faster. My prediction was accurate as I said that the higher the concentration the faster the reaction. I knew this as I had reached this conclusion the last time I did this investigation and it was also the conclusion given in the book that I referred to.
My results were quite accurate except for one anomaly on my table and on my rate of reaction graph. I think that the reason for my anomaly is that someone may have knocked into my conical flask and caused the reaction to go slightly wrong. I think this is the case as I repeated each reading three times so I got a set of reliable results and an anomaly didnt appear again. There are two ways in which I could improve my method. One is that I could use grounded marble chips instead of pieces. I would do this because the surface area will not be the same on the marble chips even though the mass is the same, this would make my results more reliable.
If I was to use pieces, the surface area isnt always the same so even though the mass of the marble chips is the same the surface area will differ, this would affect the results because the bigger the surface area the faster the reaction. If I used powder however, the surface area would be the same increases chances of a fairer test and the reaction would be quicker because the powder has a larger surface area than the chips. Because this would take less time I could also have done more repeats to get a more reliable set of results.
The other way I would improve it would be to use a burette instead of a measuring cylinder as this way I can get precise measurements. If I used too much acid the reaction would be faster causing anomalies and making my results less reliable. If I used a burette however, I would have precise measurements increasing the reliability of my results. I have a good range of results and think that I could see what the pattern would be beyond this range. I could develop my investigation in a few ways such as:
o See how temperature affects rate of reaction.
o See how the use of a catalyst affects the rate of reaction.