The investigation we are performing is about the concentration of hydrochloric acid on powdered marble, and what effect it has on the reaction and the amount of gas produced. My aim is to demonstrate how the changing concentration of the hydrochloric acid affects the amount of carbon dioxide produced when it is added to marble chips. We have performed similar experiments before which will help us to know which safety precautions to take and sensible measurements of the substances involved. The chemical reaction which occurs in my experiment is:
2HCl + CaCo CaCl + H O Factors which may affect the experiment When a reaction takes place the particles of the reacting substance must collide with each other and the activation energy must be reached for the reaction to occur. The reaction will occur if there is a collision between the particles and they produce enough energy, which results in a reaction to occur. A reaction can be speeded up, slowed down, changed and generally affected if the number of collisions is changed by changing any of theses factors.
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Pressure- this could change the reaction by compressing or expanding the CO2 produced. Gas can be compressed or expanded to fit its container. This means that we would read the gas syringe incorrectly. However, it is unlikely that the pressure would change significantly in the lab without artificial help. Temperature- An increase in temperature leads to an increase in the rate of reaction. This is due to the particles, which move faster when there is an increase in temperature. When the particles are moving faster there are bound to be more collisions.
As the particles are moving faster a large quantity of the collisions will go over the activation energy and therefore the rate of reaction increases. Obviously if temperature is decreased, then this works in the opposite way. The addition of a catalyst- A catalyst is a substance which can alter the rate of reaction but will be chemically unchanged at the end of the reaction. A catalyst works by giving the reacting particles a surface to hang on to where they can collide into each other. This also increases the number of collisions and therefore increases the rate of reaction.
The size of the marble particles- Previous experiments have shown us that if a solid is broken up into smaller particles this increases its surface area. This results in the particles around it in the solution to have more area to work on so there will be an increase in the rate of reaction because there will be more collisions. Amount of the substances- As in the surface area section. If there is more surface area to work on- and there would be if there was more marble- then there are more collisions and the rate of reaction is increased.
Purity of the substances- As in the catalyst section, though some impurities may not be left unchemically changed at the end of the reaction. This could affect the rate of reaction because there would be more collisions and so would increase the rate of reaction. These are important as if they are not observed the experiment will not be a fair test. For these reasons we will perform the experiment the same way each time we do it. We will do the experiment at: Room pressure and temperature, although we cannot keep these exactly the same all the time; but have to rely on them being almost the same.
There will be no catalyst added. We will use the same powdered marble each time. We will use 1 gram of powdered marble each time. We will use distilled water. We will use 2M HCl each time. We will use 20 cm cubed or HCl solution each time. We plan to take 4 sets of results, ranging from a 2. 5 mls of HCl in the 20 mls to 20 mls of HCl in the solution. We will take a reading of how much gas has been produced in the gas syringe every 10 seconds for 1 minute. We will then take and average from the 4 sets to give us a truer reading. Preliminary tests.
In this experiment my main task was to find out the correct amount of mass for the marble powder to use, by using different masses of marble chips, but needing to keep the concentration of hydrochloric acid the same. Prediction: Before I carried out my preliminary task I had predicted that an increase in marble chips would lead to an increase in the production or CO2 given off. I used different masses of calcium carbonate for my preliminary work, so that I could determine which mass would be appropriate for the final experiment.
The masses of the calcium carbonate were as follows: 1 g of calcium carbonate, 2 g of calcium carbonate, 4 g of calcium carbonate, 6 g of calcium carbonate, 8 g of calcium carbonate, and 10 g of calcium carbonate. I followed the same method as used in the real experiment, shown below, and eventually decided on 1g or calcium carbonate as no more was needed and it was just wasteful. We also decided on using 2M HCl because it was strong enough to make the reaction work and would still create a reaction when diluted, as we were going to be doing. Method
To keep ourselves safe, we will wear safety goggles throughout and we will use the HCl carefully so that we don’t burn ourselves. We will tuck in all stools so that n0 one falls in the lab, and do the same with bags. We will never run in the lab, and we will always carry out the experiments standing up so that if we are in danger we can move away quickly. First, we will collect out materials and apparatus. These include: 30 1g samples of medium sized marble chips, measured using a top man balance 2 M hydrochloric acid Some distilled water A gas syringe, with delivery tube and split bung attached A burette
A conical flask A stopwatch A 10 ml measuring cylinder A clamp A funnel Pen and paper to record results We set up the experiment apparatus by clamping the burette to the desk, and then filling it with HCl through the funnel. We made sure that the tap was always shut to prevent spillage. We then measured out the HCl from the burette into the conical flask, and the water in the small measuring cylinder, which we then added to the conical flask. This changed the concentration of the HCl. We then measured out several separate grams of marble chips, so that we had a plentiful supply and didn’t run out.
We made sure everything was ready, then we put the marble chips into the flask and as quickly as we could we put the bung of the gas syringe into the flask. We had to do this so that the least amount of gas possible would escape and the results would be accurate. At the same time, the other person started the stopwatch and recorded how much gas had been produced every 10 seconds, until a minute had gone by. We repeated the experiment with 20 mls of HCl and no water, 17. 7 mls of HCl and 2. 5 mls of water, 15 mls of HCl and 5 mls of water,12. 5mls of HCl and 7.