I did a number of experiments before I started my actual experiment: i) I weighed 10. 0g of CaCO3 chips, each one roughly 10-12mm large. I then placed it into a conical flask. I then added 50cm3 oh 2M HCl. All the gas that was given off was collected in a 100cm3 gas syringe. The apparatus was set up as shown below: do not tighten the clamp too much as in clamping it too tightly it would mean that the glass would be squeezed and so hinder/affect the gas syringe as it collects the gas. When I carried out this experiment I encountered two problems. 1. As soon as I put the acid onto the chips there was a lot of gas given off.
Before I could put the bung into place some of this gas escaped. The amount of gas which escaped is negligible as it only took me a second or two to place the bung into position. The fact remains that some gas did escape. However, since this is so small I chose to disregard the amount escaping. Also the volume of gas which escaped would have been replaced by the volume of gas pushed out when I put the bung into place. 2. With 10. 0g of CaCO3 and 50cm3 of 2M HCl there was too much gas being produced too quickly. What I mean by this is that I collected in total excess of 100cm3, which is the capacity of one gas syringe.
And the rate at which I collected this amount of gas was too fast for me too record accurately. Keeping in mind what happened in the first experiment I preformed a second one. This time I used 50cm3 1M HCl and 10. 0g of CaCO3. Again I found that there was too much gas being produced at a slower rate that the first but nonetheless too quick for accurate readings. I did another experiment, this time I used 10cm3 of 1M HCl with 10. 0g of CaCO3. The CaCO3 chips were still 10-12mm. The experiment was too slow. And so I decided to change the size of the marble chips to 2-4mm. In my last experiment, I placed 10.0g of 10-12mm CaCO3 chips in 50cm3 2M HCl and recorded the temperature change.
The temperature went from 21i?? C i?? 23i?? C each time. I used different amounts of CaCO3 and different amounts of HCl but it always remained the same amount of temperature rise. Therefore, although there is a rise in temperature suggesting an exothermic reaction it is quite small and so negligible. Not only this but it is the same in each experiment and so it is a constant which will not vary and hence will not cause the results to change or make the test unfair. Planning Having taken into consideration my preliminary work I chose the following procedure.
I will use 5g of 2-4mm CaCO3 chips with 8cm3 of 1M HCl and vary the molarity of the HCl from 1M to 0. 75M, 0. 5M and then to 0. 25M. I will keep the 5g of 2-4mm CaCO3 chips constant throughout each experiment. I chose 2-4mm sized CaCO3 chips because I found in my preliminary that the 10-12mm sized chips were making the reaction too slow and so if I used smaller chips it would mean an increase in surface area and so would increase the rate at which the reaction takes place. Yet it wouldn’t increase the rate so greatly that I was unable to record the results accurately.
I chose 8cm3 of HCl because then it means that I will be collecting below 100cm3 of gas in any of my experiments. I am able to prove this through a simple calculation:3 While if I chose to remain with the method set out in my preliminary work there will be no way of collecting that amount of gas. I would have had to collect 1200cm3 of CO2.
This is also proven below. I am using I chose a 100cm3 gas syringe because I will be able to collect all the gas in one syringe and there is an error margin of 0. 5% in the gas syringe. I can prove this as well. The gas syringe is graduated per cm3. Therefore you will be able to read it in between the cm3 to an accuracy of 0. 5cm3. This means you can make an error 0. 5cm3 too low or too high in an overall syringe of 100cm3. I. e. 0. 5 in 100 therefore 0. 5%. In my preliminary work I found that some gas escaped when the bung was set in place and therefore potentially alter the results.
I believe that the amount of time it takes me to place the bung into position is not of any significance and I also believe that it will take the same time to place the bung into position in each case and therefore remain a constant. I could place the bung each time after exactly 1 second has passed; this will ensure that the test is fair in all experiments. Variables and Constants My one variable will be the molarity of the HCl acid. I will change the molarity four times: 1M HCl 0. 75M HCl all four being 8cm3 in volume. 0. 5M HCl 0. 25M HCl I will keep the mass of the CaCO3 constant and the surface area.