The purpose of this experiment is to determine the effect of changing the concentration of a reactant upon the rate of a reaction.

Surface Area –           The greater the surface area of the reactants the more particles are available for a successful collision.

A Catalyst – A catalyst is a substance that changes the rate of a chemical reaction but remains chemically unchanged itself.

Concentration – Concentration effects the rate of a reaction because the higher the concentration of particles the greater the chance of a successful collision. The general trend for the concentration is the rate doubles as the concentration doubles (they’re directly proportionate).

Experiment

            To investigate the rate of reaction I have decided to use the concentration as a variable. I am going to use marble chip (Calcium Carbonate) and Hydrochloric acid. I will alter the concentration of the hydrochloric acid each time, and I will measure the amount of Carbon Dioxide product given off.

            I have chosen to use these because during the reaction Carbon Dioxide is given off, this is a gas and highly insoluble in water. The method I have planned will accommodate this.

            Though some carbon dioxide is soluble in water the amount is negligible,

At room temp (20°c) in 1l of water 1.69 ´ 10        will dissolve.

Prediction \ Hypothesis

            I think that the higher the concentration of hydrochloric acid the faster the carbon dioxide will be given off. I think this because the higher the concentration of acid molecules the more particles available to react. Also the higher the concentration of acid particles the more chance of a particle having enough activation energy. The more particles available at any one time with enough activation energy means that in a given time more of the product is produced, or it takes a less amount of time to produce a certain amount of product, in this case Carbon Dioxide. The activation energy is the amount of energy needed to make the two particles react, without it the particles would not successfully react.

Apparatus

Conical flask

Delivery tube

Measuring Cylinder ´2

Beaker

Bowl of water

Weighing scales

Stopwatch

Hydrochloric Acid Solutions and Marble chips

Method

After collecting the apparatus and arranging as followed, fill the bowl full of water and measure out 30ml of 0.5 mol acid and pour into conical flask.

Weigh out the marble chip/s, try and decide on a suitable weight because each time you will need to use the same weight. Place the chip/s into the conical flask and insert the bung.

As the reaction takes place bubbles should start to come out of the delivery tube into the upturned measuring cylinder. From the first bubble measure how long it takes for 20 ml of gas to be given off.

Record the result and refill the upturned measuring cylinder with water, wash out the conical flask and weigh out the next lot of marble chips.

Repeat the experiment but each time using a different concentration of acid 0.5 mols more each time until you get to 2 mols, you may want to repeat the experiment about three times to get a more accurate average for each concentration.

Safety

            You will be using concentrated acid, so at all times you must be very careful and you MUST wear goggles. If any spills onto your hands it should be washed off immediately and reported to the teacher.

Fair Test – Controlling the Variables

What I will keep the same –

Each time I repeat the experiment I will keep the temperature, surface area of the marble chips, amount of acid used and the amount of carbon dioxide to be collected the same. These are the other factors, which may affect the rate of reaction.

What I will change –

The only thing that I will change each time is the molarity of the acid. Each time I will increase the molarity by 0.5 mols, there is little problems with using the conical flask over because I am starting from the weaker to the stronger concentration of acid in turn.

Conclusion

            My results prove my hypothesis. The higher the concentration of acid the faster the rate of the reaction. The results also show that the research that I did also showed a valid pattern, as the concentration doubled so does the rate of reaction. Between 0.5 and 1.0 mols the amount of time roughly halves as the concentration is doubled, this is also true for the 1.0 and 2.0 mol gap. If my results had been more accurate I think the results would show the concentration of the acid and the rate of reaction to be proportional.

            The graph also supports my prediction. On the graph the steeper the curve, the faster the rate of reaction. Also from the graph I was able to work out the average rate of reaction for the gas produced.

           

Evaluation

            Overall I am pleased with my results and the way the experiment was carried  out. I think my results were fairly accurate and proved my hypothesis. To make the overall experiment results more accurate we repeated it three times and then took the average.

            If I was to do this experiment again I would probably make it more accurate by using a Burette to measure the amount of gas given off, this would measure a lot more accurately the amount of gas given off. And also using smaller particles of marble chip so I could match up surface area and weight more accurately each time. I would like to then see if the concentration of acid is proportional to the rate of the reaction.

I had only one anomalous result due to the simplicity of the experiment, this is why I chose this factor to show the effect on the rate of reaction. The only odd result that I had was the third time I repeated the experiment on the 1.5 mol solution, the reaction took place a lot faster then the previous two. I think this was due to the marble chips that we were using. At first there was a large selection of marble chips available, so finding three to match the weight that I had set was pretty easy, by the time I had to repeat the experiment for the third time it was a lot harder, so in that instance instead of three chips being used I had to use five to make up the weight, this altered the surface area giving a larger area for it to react, which is why I think the reaction went a lot faster then expected. This is also why I’m interested into investigating further the effect of surface area on the rate of reaction.

            Also other things that I would like to investigate would be the experiment of time against amount of gas produced to show at which points the rate of reaction was at best and the curve/line of reaction. I would like to also investigate other factors, which affect the rate of a reaction like temperature and surface area to see how they affect the rate of a reaction.

            Some other areas in the experiment that I feel I could have improved on were factors like, controlling the stopwatch. There is lots of room for human error here. But the inaccuracies due to them were negligible because I paid close attention to these during the experiment.

Planning Section

When dilute hydrochloric acid reacts with marble chips the following reactions occurs:

CaCO3 + 2HCL = H2O + CO2

This is the reaction we will be investigating. We will be investigating what changes the rate of reaction.

Accuracy

I hope to keep my investigation as accurate as possible in order to get the best results these are the techniques I am going to use:

æ I will start the stopwatch as soon as the first bubble of gas is seen, I will do this every time. This will also keep the results fair, as if I started before the first bubble or after the results will not be fair as I have not done the same for all the tests. This will also aid the accuracy; as if I follow the same procedure then the results will be as accurate as possible.

æ I will use a burette instead of a measuring cylinder as it is so much easier to measure a certain amount of acid, and is much more accurate. This will also help my results immensely because it is so much more accurate then a measuring because you may go over your measurement but not know it, the burette stops this because you can watch exactly where your measurement is.