Fair Test
I shall keep the variables of temperature and mass of calcium carbonate constant throughout the experiment.
Method
I will conduct the experiment in the laboratory so that the temperature will always be at room temperature. I will keep the mass of calcium carbonate the same throughout the experiment, and measure the length of time it takes for the measuring cylinder to become full of gas. The total volume of acid and water will be kept at a constant volume of 50cm³, so that the volumes of liquid used will be the same for each experiment.
I will repeat the experiment so that I can obtain another set of readings and take an average.
Safety Precautions
When conducting the experiment I will make sure that at all times I am wearing safety giggles and gloves, especially when measuring the volumes of acid to be used.
By using 50cm³ of liquid and 20 grams of Calcium Carbonate I will obtain a reasonable range of times on the clock to record the points when the measuring cylinder is full of gas.
Prediction
I predict that the greater the concentration of acid the shorter the time that will be needed to fill the measuring cylinder.
Hypothesis
A greater concentration implies more acid molecules per unit volume. This gives rise to greater probability of collisions with the marble and leads to a faster chemical reaction.
Results 1
Results 2
An average time for each concentration can now be determined:
From these results we can produce graphs, on which we can show the trends.
Analysis
The result from the graph of time against molarity confirm my earlier prediction that as the concentration of acid increases then the time taken for the gas cylinder to become full of gas becomes less.
From the first set of results when the molarity is 0.4 the time taken to fill the gas cylinder is 195 seconds. When the molarity is doubled the time taken becomes 50 seconds. This indicates that there is a much more rapid increase in the reaction for a high concentration of acid. If there had been a linear relationship between volume and molarity I would have expected to see a time of approximately 90 seconds for 0.8 mole. The fact that it was 50 seconds indicates that at certain higher concentrations there is a much greater likely hood of collisions that with weaker solutions.
Evaluation
There are obvious errors that were made in the experiment. These include:
- The measurement of the volume of acid. A pipette could have been used to measure the volume of acid to make it more accurate.
- The use of a syringe to measure the volume of the gas given off by the experiment, rather than a whole measuring cylinder. There is an error in the time for which the cylinder fills up completely. Particularly true for a high concentration of acid because the time taken for the measuring cylinder to become full of gas is so short.
- The surface area of the marble chips is very difficult to make uniform, therefore in the experiment, the best control would be to ground the marble into a fine powder and compare times. This would make the surface area of the calcium carbonate (marble) as uniform as possible.
- To keep the temperature the same. Although the experiment was conducted in the laboratory, at room temperature, this could make it an unfair test as the temperature may fluctuate. To perform the experiment in a fume cupboard, with a thermostat control would be more advisable.
- To record the volume of gas liberated every 10 seconds until each experiment continued to completion.
e.g. volume
completion
time
Conclusion
The greater the concentration of acid the shorter the time to fill the gas cylinder. This implies that the greater the concentration of acid the faster the reaction. However, the relationship between concentration of acid and rate of reaction does not appear to be a linear relationship because for higher concentrations the length of time for the experiment to be completed becomes progressively shorter.
