- Once the concentration of hydrochloric acid is made, add it to the conical flask containing medium sized marble chips, replace the bung which is connected to the gas syringe in the top of the conical flask and immediately start the stop clock. Swirl the flask 3 times so that the reaction can get going.
- Keep an eye on the gas syringe and avoiding parallax error by looking at the gas syringe from directly above. As soon as the plunger reaches 50cm³, stop the stop clock and not the time taken to produce 50cm³ of carbon dioxide.
- Repeat the experiment 3 times for each concentration for reliability. Before each repeat remember to wash out the conical flask as the results for other experiments may be inaccurate due to debris of previous experiments being left. Also remember to push the plunger of the gas syringe back in so it is at 0. This will affect our results accuracy as if the plunger is not pushed back in an inaccurate time for producing 50cm³ will be obtained.
- Note down the results and then calculate the rate of reaction from them using this formula:
Rate of reaction amount of product produced
Time taken to appear (s)
As the time each time will be how long it takes to produce 50cm³ of carbon dioxide the rate of reaction will be calculated using the following formula:
Rate of reaction = 50
Time taken to produce 50cm³ of carbon dioxide (s)
Having calculated the rate of reaction, a graph of rate of reaction against concentration will be plotted.
Safety: For safety purposes in this experiment as acid is bring used, goggles and an overall will be worn to prevent acid irritating the eyes and skin. Also the preliminary work has helped us not to perform too fast reactions that may cause the plunger of the gas syringe to fall out and break. To prevent this the procedure used doesn’t result in any extremely fast reactions.
Fair test: To keep this a fair test the other variables that could be changed must be kept constant. These have been stated below:
Temperature: Temperature must be kept constant because this will have an effect on the rate of reaction. If the temperature is altered the kinetic energy in the particles is also changed. This therefore affects the energy and frequency of the collisions, thus affecting the number of successful collisions per unit time. This again will therefore change the rate of reaction making the experiment inaccurate. To avoid this inaccuracy the experiment will all be done at room temperature so that the same temperature is maintained.
Surface area: Surface area can also affect the rate of reaction. If the solid particles are smaller, more surface area will be in contact with the other reactant, hydrochloric acid, increasing the number of collisions. So this will increase the rate of reaction. Whereas if the particles are larger, less surface area will be in contact with the hydrochloric acid, decreasing the number of successful collisions, hence declining the rate of reaction. To prevent this causing an inaccuracy, the same sized solid particles will be used, and in this experiment medium sized marble chips will used.
Amount of solid: If there is more solid to react with then obviously there will be more successful collisions between the reactants in a set amount of time, thus increasing the rate of reaction. To avoid this 5 grams of medium sized marble chips will be used each time and the mass used in each repeat for each concentration will be noted
Addition of a catalyst: The addition of a catalyst would increase the rate of reaction. This is because catalysts lower the activation energy of a reaction. When a catalyst is present it adsorbs the reactant on to its surfaces, where they can collide more easily. Therefore if a catalyst is added to the reaction, it will increase the number of successful collisions, thus increasing the rate of reaction. To keep this experiment a fair test, I have decided not to use a catalyst at all.
Pressure: Increasing the pressure would also increase the rate of reaction. If the pressure of a reaction is increased, it means that the particles are more squashed together. If the particles are more squashed together, therefore are inevitably going to be more successful collisions per unit of time, thus increasing the rate of reaction. To prevent this factor affecting our experiment, the entire experiment is going to be done at atmospheric pressure i.e. 1
Prediction: I predict that as the concentration increases the rate of reaction will also increase. I also expect the relationship between concentration and rate of reaction to be directly proportional.
I think that the graph will look like this:
Reasoning behind prediction: Concentration is the measure of how many particles there are of a certain substance in the fixed volume solution. I this case how many hydrogen chloride molecules there are in 50cm³ of hydrochloric acid solution. The concentration would be low if there were fewer of these particles and increase as more of the number of these particles increase. The range of concentrations mentioned in the method are related to the proportion of how many particles of hydrogen chloride there will be. As 2M hydrochloric acid is going to be used the concentrations going to be made will be lower than these as the concentration can not be increased unless more hydrogen chloride molecules are added to the same volume of 2M hydrochloric acid. However dilutions can be made by adding distilled water and 2M hydrochloric acid. This is because there is a set volume of hydrochloric acid to be made, 50cm³, but the volumes of hydrochloric acid and distilled water added together to make these solutions differ. When less hydrochloric acid but more distilled water is added the concentration will be lower as there are overall less hydrogen chloride molecules in the solution. On the other hand if more hydrochloric acid but less distilled water is added, the concentration will be higher as there are comparatively more hydrogen chloride molecules in the entire solution. For example as shown below container 1 and container 2 have the same total number of particles, however container 2 has a higher number of red particles, thus showing that it has a higher concentration of red particles in comparison to container 1, which only has 3 red particles.
In this experiment the mass of marble chips is going to be the same. Therefore if the concentration of the hydrochloric acid increases, it results in the rate of reaction being quicker. This would be because as the concentration increases the number of hydrogen chloride particles in the solution would also increase. If these increased it obviously means that the number of successful collisions will be higher as there are more particles therefore more chances for successful collisions between the hydrogen chloride and calcium carbonate particles. As there are more chances there would again more likely be more successful collisions between the particles, thus increasing the rate of reaction.
I also predict the rate of reaction to be directly proportional to the concentration. I predicted this because if the concentration is doubled, there are double the numbers of hydrogen chloride molecules in the hydrochloric acid solution, therefore there is obviously double the chances of successful collisions. If there are double the chances, there are going to be double the number of successful collisions between the hydrogen chloride and calcium carbonate particles, which will decrease the time of reaction by a half as the reaction will happen quicker. If the time is halved, it will in turn double the rate of reaction. Therefore if the concentration is doubled the rate of reaction will also double.
