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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.
- 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.
