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1. How does reaction rate change according to concentration?
Based on our processed data, the lower the concentration the faster the reaction. This also means that the higher the concentration, the slower the reaction.
2. Why is the cotton wool plug needed?
The cotton wool plug is needed to absorb the amount of carbon dioxide released. It acts as a sponge in absorbing the gas expelled from the conical flask. The cotton wool is weighed beforehand and then after absorbing carbon dioxide, to find the mass of carbon dioxide released. The amount of carbon dioxide released can be used to calculate the rate of reaction.
3. Why is there no further loss in mass at the later time intervals?
Eventually, there aren’t enough remaining moles of HCl to react with the calcium carbonate marble chips. Thus, there is no more reaction and there is no carbon dioxide to be expelled.
4. How could reaction rate be calculated from your graph?
The first graph shows the loss of carbon dioxide over time. In this experiment, the rate of a reaction may be measured by following the rate at which carbon dioxide is formed. It is equivalent to the amount of carbon dioxide formed divided by time. The gradient of the graph can be used to calculate the rate of reaction, because the gradient is equal to a change in the y values over a change in the x values. In this graph, it would be equivalent to a change in the loss of carbon dioxide over a change in time. This shows the rate of reaction and how fast it is going. Based on the graph, the steeper the slope, then the faster the reaction and vice versa.
Conclusion and Evaluation
In this experiment, the effect of concentration on rate of reaction was investigated. We did this by reacting marble chips (calcium carbonate) with hydrochloric acid, and recording the expelled mass loss of carbon dioxide as the concentration of hydrochloric acid began to drop. The carbon dioxide loss in mass over time was used to calculate the rate of reaction.
In chemistry, the rate of reaction is used to describe how quickly a reaction happens. It is defined as the measure of the amount of reactants being converted into products per unit amount of time. In our case, we measured the amount of hydrochloric acid and calcium carbonate being converted into carbon dioxide in 20 seconds intervals. There are several ways to vary and experiment with a rate of reaction. Students can observe a change in volume of gas produced, change the transmission of light in the experiment, change the concentration using titration or even change the concentration using conductivity. For this experiment, we observed rate of reaction by a change of mass.
We calculated our rate of reaction by dividing the grams of carbon dioxide released by 20 seconds. Because 20 seconds was a constant divisor, the more mass of carbon dioxide released, the greater the rate of reaction. We also calculated the concentration of HCl left and observed the relationship. Based on our processed data, the lower the concentration, the greater the rate of reaction. For example, after 320 seconds, 2.00 g of carbon dioxide was expelled when the concentration of HCl was 0.182 mol dm-3.
This gives a rate of reaction of 0.1 g of carbon dioxide produced per second. At 20 seconds, 0.70 g of carbon dioxide was released when the concentration of HCl was a whopping 1.364 mol dm-3. This gave a rate of reaction of 0.035 g CO2 per second, which is 0.065 g more than the aforementioned low concentration. The two graphs confirm this conclusion. As time goes on, the mass of carbon dioxide expelled increases, while the concentration of hydrochloric acid decreases. A lower concentration of hydrochloric acid causes more carbon dioxide to be expelled and thus lead to a greater reaction rate.
I was quite shocked by our results. I thought that with a higher concentration and more molecules moving around, there would be a better chance of reactions taking place. However, this experiment shows that it was in fact the other way around. Perhaps, with a lower concentration of hydrochloric acid, there needed to be more carbon dioxide expelled to balance out the equation. With fewer moles of hydrochloric acid and lower concentrations, the equation was most likely out of proportion. In an attempt to make up for the lower number of moles, more carbon dioxide was released.
Tearing of cotton wool when it was being removed from the flask and then losing the torn cotton.
When the cotton wool was being removed, some it may have been torn off. As a result, the mass could be a lot lighter than it should have been. When taking out the cotton, damage should be limited so that everything is accounted for and a more accurate carbon dioxide mass is achieved.
Be very careful when removing the cotton to avoid any tearing. If a piece of cotton is accidently torn off, do not throw it away! Keep it and weigh it so that it is accounted for.
Experiment was not performed until carbon dioxide stopped being expelled.
The data was limited. Carbon dioxide was still being produced and there were still 0.091 moles of hydrochloric acid left when the experiment was stopped.
Do not finish the experiment until there is no more carbon dioxide being expelled. This way, we get a better idea of the limits and possibilities of the reaction rate and how far it can go.
Timer was not started the same time the marble was entered.
Some marble could have been left inside the solution for a longer or shorter time than others. As a result, carbon dioxide values could be lower or higher than they should have been.
The timer should be alert and there should be communication between the partners. The timer needs to begin once the marble chips are placed inside, and it needs to be removed right after twenty seconds. By maintain a steady time of twenty seconds, we can properly assess the reaction rates without adding another independent variable of time.