Since I’ve decided to measure the CO2 output, I will need an accurate way of measuring how much CO2 is being produced. In earlier experiments, we used to count the number of bubbles produced. As our results proved, this was an inaccurate way of measuring gas output. To get more accurate results, after the chips have been weighed out I will fill a measuring cylinder with water and place it upside down in a bath of water. Next, I will place the end of the delivery tube at which the CO2 exits at the opening of the upside down measuring cylinder. The produced CO2 will displace the water within the measuring cylinder causing it to flow into the surrounding water bath, thus giving me a reading of the gas produced from the reaction. The amount of CO2 produced can then be read off in milliliters (ml). I will keep the measuring cylinder up by using a retort stand.
When this has been done, I will drop the calcium carbonate into the dilute hydrochloric acid. As soon as I have done this, I will seal the test-tube with the bung plug and start the stopwatch. In order for me to get an accurate set of results, I have decided to allow the marble chips and the dilute hydrochloric acid react for 3 minutes. I have decided to allow them to react for 3 minutes because I believe this is adequate time for the reaction to take place, giving me more accurate results and a more precise graph.
Prediction: I predict that the greater the concentration of thiosulphate solution, the faster the chemical reaction will take place. Therefore, the cross will disappear more quickly due to the cloudiness of the solution. I have made this prediction based on the Collision Theory. This theory means that there are four factors that can affect the rate of reaction between the marble chips (calcium carbonate) and hydrochloric acid in this experiment. These factors are: the concentration of the hydrochloric acid, the temperature of the hydrochloric acid, the surface area of the marble chips and the mass of the marble chips.
The equation for this experiment is:
Thiosulphate + Hydrochloric Acid Sodium Chloride + Hydrogen Oxide + Sodium Oxide + Sulphur
The Collision Theory states that a reaction occurs when particles collide. Because of this, the concentration of the acid will affect the rate of reaction. This is because changing the concentration will alter the ratio of acid particles to water particles. If the concentration of hydrochloric acid is high, there will be more acid particles in the same volume, meaning that there is a greater chance of the particles colliding with the calcium carbonate particles. An increased chance of colliding means an increased chance of reacting meaning that the rate of reaction would increase. Therefore, decreasing the concentration of hydrochloric acid would have the opposite effect. Having less acid particles would mean that they have a lesser chance of colliding with the calcium carbonate particles.
Temperature also affects the rate of reaction. When particles are hotter, they vibrate more as there is more energy (heat) from the surroundings to use. Conversely, when particles are cold, there is less energy that can be used for vibration, resulting in them vibrating slower. For instance, when water molecules reach a certain temperature (100oC), they vibrate so quickly that they vibrate further away from each other, turning the liquid into a gas. In addition, when the water molecules become cold (0oC), they vibrate so slowly that they stop sliding over each other like liquids do, and therefore turn the water into ice.
Therefore, if the particles are hot, and vibrate quickly, there will be a greater chance of collisions occurring. If there is a greater chance of collisions occurring, the rate of reaction will increase in turn. As a result, if the hydrochloric acid is hotter, the rate of production of CO2 will increase. Equally, if the hydrochloric acid is cooler, the particles will not be vibrating as quickly meaning they will not be making as many collisions, resulting in a slower reaction rate.
In addition to temperature and concentration, surface area also affects the rate of reaction by increasing or decreasing the amount of calcium carbonate molecules that are available for the acid molecules to collide with. If the surface area is small (large marble chips), the acid particles have a smaller surface area to react with even though the volume is the same. Regardless of the total amount of molecules in the chip, only the molecules on the surface will collide (react) with the hydrochloric acid. Therefore, if the marble chip was large it would have less surface area than smaller marble chips equalling the same mass. Therefore, if the marble chip was ground into a fine powder, then more particles would be available for reacting with the acid, resulting in a very fast rate of reaction. Because of all this, the larger marble chips would not react as efficiently as the smaller chips.
Ultimately, the rate of reaction is affected by how many particles collide within the allotted time. Temperature, surface area and concentration can change this.
Fair Test: To make this experiment a fair test, I must consider many things.
For instance –
- I will only vary one thing – the concentration of the Hydrochloric acid and Thiosulphate solution.
- I will conduct all the tests at room temperature because, as I mentioned in the prediction, temperature has an effect on the rate of the reaction.
- The measures of Hydrochloric acid will always equal 50ml.
- The person timing the experiment will look for the disappearance of the cross, otherwise there would be a time lapse between seeing the cross disappear and telling the other person to stop the clock and then eventually stopping the clock.
Safety: To conduct my experiment safely I will follow normal laboratory rules, which include:
- The wearing of safety goggles to protect my eyes from chemical splashes.
- Standing up to conduct the experiment, therefore reducing the risk of tripping and spilling chemicals.
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Taking care when handling chemicals, particularly Hydrochloric acid and Thiosulphate because they are irritants. I will not touch my eyes or mouth until I have thoroughly washed my hands.
- Taking care when using glassware to prevent injury.
Table of Results:
On the next page, I have drwan a graph -
Conclusion: I conclude that the more concentrated a reactant is, the quicker the rate of reaction time will be.
I have come to this conclusion because of several reasons. Firstly, my results give conclusive evidence that as the amount of Thiosulphate decreases, and the amount of water increases in the solution, there are less reactive atoms to collide and therefore less successful collisions causing little chemical change so the reaction rate is slower. In a more concentrated solution, there are more atoms to collide so the reaction time is quicker.
My results support the prediction I made because I said ‘the greater the concentration of thiosulphate solution, the faster the chemical reaction will take place.’ I believe I was correct and a secondary sources from the Internet state that the reaction time will be faster with a more concentrated solution because, ’the more molecules there are, the frequency of successful collisions is greater and therefore the reaction rate is speeded up.’
Evaluation: I think that overall, my experiment was a successful one. Although, I think I could’ve made some improvements, such as I only obtained three sets of results and then worked out an average. To make my average more accurate, I could have done more tests to gain a more reliable average.
I think there is also a human error factor involved when you are measuring liquids and looking for an end point in the reaction. Although the reaction I chose had a fairly definite end point, it was still hard to tell whether the whole cross had disappeared or not. Instead of using a cross, a laser, or maybe an interactive quasar beam could be used and when the beam does not make contact with the sensor, that would be the definite end point. A better standard of beaker could also be used, as well as a less contaminated bottle of thiosulphate, as our bottle contained thiosulphate AND hydrochloric acid already.
In addition, I also had no anomalous results in my experiment, which only proves that I carried out the experiment properly and correctly.
