Rates of Reaction Investigation

Background Information

Particle

This says that everything is made of atoms and depending on their properties, the object is one of the three states of matter – Solid, Liquid or Gas.

SOLIDS – Have a fixed position and are hard to compress. The particles have strong forces of attraction and are usually very dense.

LIQUIDS – Don’t keep a certain shape and take the shape of the bottom of the container. These cannot be compressed easily and are quite dense. There is some force of attraction between the particles.

GASES – These do not have a definite shape but they take the shape of the container they are in. They are easily compressed and there is no force of attraction between the particles. They also have low densities.

Collision

This theory details the conditions that are needed for a reaction to happen and how a reaction can be increased. For a reaction to happen, particles have to collide, and collide with enough energy to break and then remake bonds. The four things that can speed up a reaction are:

Temperature – higher temperature gives the particles more energy and therefore more collisions occur
Pressure – the closer the particles, the more likely they are to collide
Surface area – if larger objects are broken down, there is more area to be collided with
Catalyst - speeds up the rate of reaction without being used up itself. It gives the particles something to attach to where they can bump into each other

This information was obtained from the SEG Modular Science Revision Guide, Volume I, 2000.

Aim

I aim to find how different strengths of acid affect the rate of reaction with marble chips / calcium carbonate. I will do this by putting 1g of marble chips into 25ml different strength molar hydrochloric acid in a conical flask and seeing how much carbon dioxide gas is given off.

Prediction

I predict that the stronger the strength of acid, the more carbon dioxide will be given off and therefore the weaker the hydrochloric acid, the less gas it will give off. I expect this to happen because the higher the concentration in a reaction, the quicker the reaction will be because there are more particles to collide, and consequently react, with. The reaction time depends on how many successful reactions take place because even though the particles have added energy causing them to ram into each other more often, they need enough energy to be able to break the existing bonds and make new ones. I think this will happen because of the laws in the Collision Theory stating that “For a reaction to happen, particles have to collide, and collide with enough energy to break and then remake bonds”. It also says that “the closer the particles, the more likely they are to collide” which means that with higher concentration acid containing more acid particles, all the particles in the solution will be closer, hence more collisions will occur.

Method

In the experiment I am going to carry out, I am looking to test how different strengths of acid affect marble chips / calcium carbonate. I will do this by putting 1g of marble chips into 25ml ½ molar hydrochloric acid in a conical flask and seeing how much carbon dioxide gas is given off. This will be done by using a gas syringe fixed over the conical flask and recording the amount of gas given off every 30 seconds for 360 seconds.

I will do the experiment 3 times and take an average to make the ...

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Method

I will do the experiment 3 times and take an average to make the results accurate. Next I will test the other strengths of acid, which are 1molar, 1¾ molar and 2molar, again testing each strength 3 times. If the first two results are similar, I will not bother with a third.

I will make the experiment a fair test by making sure it is always 1g of calcium carbonate being used, each test with the same strength molar is done in the same conditions and the glass syringe will be returned to the end at the start of each test. I will also dry the marble and conical flask before reusing them.

I would expect that the higher the strength of acid, the more gas is given off in the time because in the collision theory outlined earlier, the higher the pressure, the faster the reaction.

Equipment

12 x 1g Calcium carbonate
12 x 25ml Hydrochloric Acid
Conical Flask
Gas Syringe
Rubber bung with tube through it
Stop clock
Goggles
Measuring cylinder
Measuring scales

Table of Variables

Fair Test

I will make the experiment a fair test by testing each strength of acid three times, or two if they are close, for accuracy and do all of the experiments for one strength on one day so that the room conditions do not vary. Also I will follow the table of variables above and only change one variable.

The diagram below shows the hydrochloric acid reacting with the calcium carbonate and giving off carbon dioxide, which is rising and then escaping through the tube in the rubber bung to the gas syringe where the arrow illustrates the direction in which the carbon dioxide pushes the syringe.

My results show that the higher the concentration of acid, the more carbon dioxide it gives off. The graph supports this along with it showing that the higher the concentration, the faster the reaction as the curve of best fit is steeper as the concentration of acid increases.

My graph also shows that towards the end of the experiment, the rate of reaction decreased. This was because as the hydrochloric acid reacted with the calcium carbonate, it created water and the water particles were colliding with the other reactants, slowing down the original reaction because as the water particles were colliding with the other reactants in the experiment, fewer reactions between the hydrochloric acid and calcium carbonate particles could take place.

My original prediction was:

“I predict that the stronger the strength of acid, the more carbon dioxide will be given off and therefore the weaker the hydrochloric acid, the less gas it will give off.”

The results that I have obtained show this prediction has been correct.

Conclusion

I have found that the stronger the strength of acid, the more carbon dioxide will be given off and therefore the weaker the hydrochloric acid, the less gas it will give off. This was because with a higher concentration of acid, there are more particles to collide with. This is shown on the graph because as the acid concentration increased, the curve of best fit finished higher than those of weaker concentration.

The results that I obtained are consistent with my original prediction, which was:

“I predict that the stronger the strength of acid, the more carbon dioxide will be given off and therefore the weaker the hydrochloric acid, the less gas it will give off. I expect this to happen because the higher the concentration in a reaction, the quicker the reaction because there are particles to collide, and consequently react, with.”

The balanced equation for the reaction between 25ml hydrochloric acid and 1g calcium carbonate:

CaCO3 + 2HCl CaCl2 + H2O + CO2

The above equation shows that as the reaction is happening, H2O is being given off and these water particles are slowing down the reaction by colliding with the other reactants in the experiment causing fewer reactions between the hydrochloric acid and calcium carbonate particles. This means that less CO2 is being given off which explains the curve in the end of the lines on the graph shown previously.

I believe that my experiment to find whether concentration affects the rate of reaction went well as I completed it safely and on time with my results showing that my prediction was correct.

The results that I obtained are quite accurate although they could have been more exact by carrying out all the experiments on one day so that room conditions were the same and the measuring of the carbonate mass and the volume of the acid was done by eye only. Also, I could have used a graduated pipette to measure out the acid, as this would be more accurate. The surface area of the calcium carbonate could also have affected the rate of reaction and I could have made it fairer by crushing the marble chips.

I feel that the method I used was good and reliable because I was able to finish the experiment in the time allotted and I was able to obtain all my results easily and efficiently. Another way to do the experiment would be to find the weight of the calcium carbonate before and then after the experiment to find the change in mass. I believe that this would give the same, or similar results, i.e. the stronger the concentration, the larger the change in mass. I could also have measured the surface area before and after the experiment as I predict this would give the same pattern of results although this would be impractical to measure. Another variation of this experiment would be to put the hydrochloric acid and calcium carbonate into a conical flask and place cotton wool in the top to stop splashes escaping but still allowing Carbon Dioxide to escape. I would measure the mass of the solution at the start and then at 30-second intervals for 6 minutes. I believe this method would give the same pattern of results as the experiment that I performed.

My results are reliable as they show a clear time difference between the different experiments with their being no anomalous results, although the 1 and 1½ M experiments were very close with the other two being vastly different. This could have happened because the room conditions could have been significantly different to when the other experiments were carried out.

If I were to provide more results, and therefore improve the accuracy of them, I would’ve needed a great deal more time than was physically possible to allocate.