There are seven factors that affect the speed – or Rate of a Reaction.
- TEMPERATURE
- STATE OF DIVISION
- CONCENTRATION
- PRESENCE OF CATALYST
- PRESSURE
- LIGHT – Wavelength/ frequency
- AGITATION
Temperature –this is not really a worry because of our climate not changing that much from week to week.
State of Division – we will be using this as one of the factors we are changing. This is to see if the reaction will speed with different sizes of chips. In all cases, the same overall weights of chips were used to ensure consistency.
Concentration – this is our other ‘variable.’ We are using this to see if the more concentrated the acid is, will the reaction be quicker?
Presence of catalyst – we do not need a catalyst because our reaction is quite quick by itself.
Pressure – this will not change inside our lab.
Light – the light will be the same inside the lab.
Agitation – we will not stir the reaction.
THE METHOD:
Marble chip and the Hydrochloric acid will be placed in a conical flask, when they touch each other the reaction will begin.
A thistle funnel is placed in the top of the beaker to prevent any liquid spilling over a desk.
Because of the fact that the marble chips come with a thin layer of powder on the outside, we have decided to leave the reaction for thirty seconds at the beginning before we start collecting the Carbon Dioxide.
After the thirty seconds, we placed a boiling tube (50cm3) on top of the glass tube coming from the conical flask and timed to see how long it takes to fill the tube completely with the Carbon Dioxide.
We will also measure the temperature of the room, because it may be carried out on different days so the temperature could have changed. This temperature change could affect our results by many seconds.
I believe that my prediction that “ the more concentrated the acid, the quicker the reaction will be,’’ will be proven correct because stronger acids come with more severe warnings on them, thus must be more corrosive. The more corrosive an acid is the faster it should make this reaction happen.
The equation is
CaCO3 + 2HCl CaCl2 + H2O + CO2
Firstly we tested the different chip sizes and came up with these results.
This clearly shows that, the bigger the chips are, the longer it takes to fill a 50cm3 boiling tube. We used 2 Molar acid to do this, and used it every time so as the test was kept fair.
I then drew up these graphs to show the correlation between the size of the chips and the time taken.
From my graph I have shown that my prediction was correct, as the Line of Best Fit is a straight line through the origin, proving that the Concentration of HCl is proportional to the size of the chips.
Concentration of HCl affects the speed of the reaction because the number of atoms in the reaction increases or decreases as the size of the chips increases or decreases in proportion.
Next we tested the different concentrations of Hydrochloric acid.
In the beginning I said that I thought that the more concentrated the acid is, the quicker the reaction would happen, here are the results.
I then drew this graph to show how the time changes as the concentration changes.
Were my predictions correct?
After doing both experiments I think that my results did in fact match up to my predictions except when changing the Concentration of HCl. The results were going to plan until it reacted 2.0 Molar. At this stage the 2.0 and 2.5 molar took exactly the same time to fill the boiling tube. This may have been human error because the HCl was made by a technician and might have been wrongly made i.e. the 2.5 molar may be weaker or the 2.0 may be stronger then they were supposed to be. I would have expected it to take less time because the more concentrated an acid the stronger it is, thus should make the reaction go faster.
My prediction that the smaller the chips, the faster the reaction was correct because there is more surface area for the acid to react with. The results back this up because it shows that the quickest reaction was the small chips because they have a very large collective surface area and thus will react quickly. Next to fill the test tube was the medium sized chips, they have a lesser surface area then the small chips but more than the big chips. Then the slowest to fill the boiling tube were the large chips, this is because they have the least surface area and will react slower.
I think that my results are very reliable. They met my predictions, which were made using the science I have been taught over the past five years. All my readings were repeated and an average was taken. If there were an anomalous result they were re-tested and changed accordingly. My equipment was kept the same the whole way thought the experiment so the only things that were changing were my variables. This means that my experiment was a fair test thus the results are as reliable as they could be.
After doing my experiment and analysing my findings I can now say that there are two clear conclusions
The more concentrated an acid is the faster it will react
The larger the surface area of a reactant the faster the reaction will be
Because of the fact that my experiment met my expectations and the exportations of basic science, I would say that my experiment has nothing that needs changing. I am very happy with the way my experiment went and with my method.
However it would have been nice to get all the results done in the one day, because there could have been different factors that could potentially have affected my work, e.g. using different apparatus, the apparatus I am using may have other chemicals left in it, or there could have been a small temperature rise, that was not noticed on the thermometer, these are all small things that could affect my results in a big way.
