Mass of marble chips – so that the reactivity is similar
- We will conduct two experiments for each concentration, so that we can find the average of the two and get a more accurate and reliable result
- Use similar sized and shaped pieces of marble – to make sure the surface area of the chips does not become a factor in how fast the reaction is
- Use the same bottle of acid for each experiment in case the pH of it varies from different sources
- Conduct all experiments at room temperature – so that the temperature does not affect the rate of reaction
Trial Experiment –
We did a trial experiment to make sure we knew what we would be doing when conducting the proper and also to see if the measurements we are used are suitable.
For my trial experiment I used:
-
100cm measuring cylinder
- 3g marble chips
-
20cm of acid
By conducting my trial experiment, I found out that 3g of marble would be too big as the reaction was be too fast to record and the 100cm measuring cylinder was too small as too much gas was produced.
For the actual experiment I will use:
-
500cm measuring cylinder
- 2g marble chips
-
20cm of acid
Acid concentrations -
-
2 molar = 20cm of hydrochloric acid + 0cm of water
-
1.5 molar = 15cm of hydrochloric acid + 5cm of water
-
1 molar = 10cm of hydrochloric acid + 10cm of water
-
0.5 molar = 5cm of hydrochloric aid + 15cm of water
Method -
- boiling tube
- delivery tube
- test tube rack
- clamp stand
- water bath
- marble chips
- top pan balance
- hydrochloric acid
- water
- measuring cylinder (we will use the smallest measuring cylinder possible to collect to the gas, especially with the lower concentrations, otherwise it would not be accurate enough)
- Set up experiment as shown in the diagram
- Weigh out 2g of marble chips and measure 1st concentration of acid
-
Put marble chips in boiling tube and pour 20cm of 2M acid
- Place the bung securely on the top of the boiling tube quickly to prevent gas escaping
- Start the stop clock when the bung is in place and proceed to measure the volume of carbon dioxide using the measuring cylinder every 20 seconds for 200 seconds
- Repeat this procedure for each concentration
Results -
Conclusion –
The results and the graph prove that as the concentration of the aid increases the volume of gas produced also increases. These results agree with my prediction. We can see this is true on the graph because as the concentration of acid increases the steeper the gradient of the graph, meaning that the volume of gas produced also increases. When the concentration of acid is 0.5 molar, the volume of gas produced after 100 seconds is 28.5cm and after 200 seconds it is 47.5cm. When the acid is 1 molar, the volume of gas produced after 100 seconds is 61.5cm and after 200 seconds is 98.5cm. At 1.5 molar, the volume of gas produced after 100 seconds is 87.5cm and after 200 seconds is 140cm. When at 2 molar, the volume of gas produced is 143cm and at 200 seconds is 207.5cm. This clearly shows an increase in the in the volume of gas produced as the concentration of the acid. If the acid is 2 molar, it is very concentrated, which means there are lots of acid particles in the solution, this means that the chance of acid and marble particles colliding with each other would be more likely. The more that the particles are colliding with each other the quicker the marble will decompose and therefore give off gas quicker.
Evaluation –
The results obtained from my experiment are fairly reliable; I can see this from my graphs as my results are nearly always touching the line of best fit. I cannot see any obviously anomalous results. Any slight errors could have been caused by the following factors. Some of the equipment we used in the experiment could have led to errors; for example, we used a measuring cylinder filled with water to measure the volume of gas produced. This could have been a source of error as the measuring cylinder might not have been totally full of water when turned over, meaning that there would already have been some gas in the measuring cylinder, making our results slightly wrong. Also there could have been a leak in the delivery tube or it may not have been totally under the measuring cylinder, therefore some gas may have escaped. Another source of error could have been the size and shape of the marble chips, as they were different sizes, they would have different surface areas meaning that some chips would be breaking down quicker than others would. A small source of error could have been how quickly the bung was placed on the test tube, because it had to be put on after the marble chips had started reacting there would have been some gas lost. Also the way we measured out the different concentrations of acid was not very accurate, this could have lead to slightly wrong results.
We needed to repeat the experiment for each concentration at least twice because if we didn’t the results we found could have been a total fluke, whereas when we did it twice, it was less likely that our results were totally wrong. Also doing the experiment more than once would improve the accuracy and reliability of our results. We have enough results to conclude that as the concentration of the acid increases the volume of gas produced also increases, but our results would be more exact if we were to conduct the experiment a lot more times.
To improve this experiment, if I was going to do it again, I would conduct it at least four times for each concentration so that our results would be more reliable. I would also rule out any errors caused by the difference in the surface area of the chips by grinding the marble chips so that they were all the same size or I would use marble powder. I would also use professionally prepared concentrations of acid to rule out any possibility of errors in the making of the different concentrations of acid. I would also continue the experiment for another 100 seconds to see whether the volume of gas produced gets smaller as all of the marble chips have broken down. To eliminate any errors caused by the putting the bung in the test tube, we could use a gas syringe to collect all the gas produced without loosing any at the start. As another way of testing the concentration of acid, we could the experiment differently by measuring the mass of the acid and marble before and after the experiment to see which of the concentrations had lost the most mass.