Prediction
I predict that as you increase the concentration of the hydrochloric acid the rate of reaction with the marble chips will also increase. I think this because by doubling the concentration of the hydrochloric acid you are creating double the amount of reactants in the reaction. This therefore means that you are doubling the amount of collisions and as collisions are needed for the particles to reform you are doubling the rate in which the reaction takes place. The diagrams below explain this in more detail.
Plan
To test my aim I am going to react hydrochloric acid with marble chips. To investigate how concentration of hydrochloric acid affects the rate of reaction with marble chips I am going to test 5 different concentrations of hydrochloric acid. These are 0.5 moles, 1 mole, 1.5 moles, 2 moles and 2.5 moles. These different measurements should be sufficient in enabling me to draw a conclusion from this investigation. I will measure the rate of reaction by timing how quickly the carbon dioxide produced in the reaction displaces the water in the test tube. I will start the stop watch as soon as the hydrochloric acid is added to the marble chips.
I will need certain apparatus to perform this investigation with enough accuracy to draw some conclusions at the end. I will need:
- 6 test tubes (one where the carbon dioxide displaces the water)
- 1 dispensary tube
- 1 bowl half full of water (this part doesn’t have to be accurate as long as the water level is above the bottom of the test tube)
- 5 different molar concentrations of 25cm of hydrochloric acid (shown below)
- 5 batches of 1mg of marble chips (explained below)
- Stopwatch (0d.p. as there is no need because there is inaccuracy in the human reaction time to put the bung on)
- 1 bung to trap the carbon dioxide produced and allow it to flow into the dispensary tube
I will set up the apparatus as shown below:
I will test each of the different concentrations of hydrochloric acid 3 times to make the results as accurate as possible. Obviously the method of adding the bung once the hydrochloric acid has been added is inaccurate so there is no point in measuring the time to 2d.p.
To make sure the test is fair I will have to make sure that when the test tube (used for displacement) is re-filled, the whole of the test tube is filled as to stop gas building at the top and therefore reducing the amount of water to displace. I will also have to consider several different factors (mentioned earlier) which affect the rate of reaction:
- Temperature
As the temperature is increased, particles have more energy and move faster. When particles are moving faster they are more likely to collide and therefore, as collisions are needed for the reaction to take place the rate of reaction will increase.
I will overcome this factor by making sure that the tests are done in similar conditions. E.g. not doing one near a window providing heat energy and the others in the shade where there is less heat energy. Obviously, due to inaccuracies which will take place whilst the bung is being placed on the test tube this factor doesn’t have to be kept totally equal.
- Surface Area
The smaller the particles the larger the surface area and the greater the number the articles exposed which can collide, leading to a faster rate of reaction.
I will overcome this factor by making sure that similar sizes of marble chips are included in the 1mg batches. For this factor to be kept equal powdered marble must be used. I may consider using powdered marble if it is available at the time of the experiment as it will improve the accuracy of the investigation.
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