The word equation for the reaction is:
Calcium Carbonate + Hydrochloric Acid → Calcium Chloride + Carbon Dioxide + Water
The balanced formula equation is:
CaCo3 (s) + 2HCl (aq) → CaCl2 (aq) + CO2 (g) + H20 (l)
Apparatus
Clamp and Boss
Gas syringe, delivery tube and bung
100ml conical flask
50ml measuring cylinder
10 ml graduation pipette and filler (to measure liquid)
Stopwatch
Thermometer
Watch Glass
Weighing boat
Distilled water
Fair Test
To acquire accurate results, many measures need to be taken to keep the experiment as fair as possible. All variables within the investigation must be kept constant throughout, so as to obtain results that are true to all circumstances. 20g of marble chips will be used in each concentration of acid. A top pan balance will be used to measure this 20g of marble chips accurately. As for the acid, it will always be hydrochloric. The temperature of this will be the same in each experiment, (this temperature being room temperature) controlled by a warm/cool water bath. The same volume of the acid, 40cm3 will be used each time also.
The same apparatus will be used each time. This is in case there is a fault in the apparatus, such as a leak. By using the same equipment during the whole experiment, the same fault stays throughout and this keeps the results fair, although slightly inaccurate.
Prediction
I predict that the stronger the concentration of the hydrochloric acid, the faster the rate of the reaction will be. This is because of my knowledge of the “collision theory”. This is the theory that for reactions to take place, the particles in the reactants must collide. They also must do this with sufficient speed and energy. When the concentration of a reactant is increased, there are more particles in the reaction. This means that there is more chance for collisions of the particles. So therefore, by increasing the concentration in the experiment, there will be more collisions of particles, and this will make more energy, and increase the rate of reaction.
Method
I attached the boss clamp to the retort stand and fastened the gas syringe onto it. I measured, using a pipette and filler, 10cm3 of hydrochloric acid at room temperature into a measuring cylinder. I then poured this acid into a conical flask. Then using the pipette filler, I poured 30cm3 of water into the same conical flask as the hydrochloric acid. There was now 0.5M of hydrochloric acid in the conical flask. The starting temperature was taken, and controlled with a bath of warm water. Next, I measured into a weighing boat 20g of large marble chips, using the weighing scales. These were washed, using distilled water and a watch glass, to rid them of a dust coating.
I poured these chips into the conical flask, and then quickly put the bung onto it, and started the stopwatch simultaneously. Then I observed the gas syringe. For every 10cm3 of gas that was produced, I recorded the time it had taken to get to this amount, on a results table. The time was recorded up until a volume of 100cm3 of gas had collected in the syringe. I did the same experiment two more times, with the same concentration of hydrochloric acid. After each experiment I washed the marble chips with water, to stop the reaction.
The next time I did this experiment, I measured out 20cm3 of hydrochloric acid into the conical flask, and then 20cm3 of water. The hydrochloric acid now had 1M of concentration. I repeated the same investigation as before with this concentration of acid three times. Next, I measured 30cm3 of hydrochloric acid and 10cm3 of water into the conical flask and did the experiment three times. In this case, the hydrochloric acid was 1.5M. Finally, I measured out 40cm3 of hydrochloric acid into the conical flask, with no additional water. The concentration of the acid here was 2M. The experiment was carried out three times with this concentration. For each concentration of acid, the same chips were used, however for each new concentration, new chips were used as the surface area of the previous would have changed after three experiments, and this would not have made the experiment fair.
An average of the three different sets of results for each experiment was taken, and recorded on a results table.
Obtaining Evidence
Analysing Evidence
According to results tables and graphs, the results that I obtained seem quite reliable. The results for the 2M concentration of hydrochloric acid seem slightly more curved than should be expected.
The trends that I can see from the first graph are that as the concentration of the hydrochloric acid increases, the time taken to produce a set amount of carbon dioxide gas decreases. This is seen by a steeper line for 0.5M, and a sudden drop of gradient in the 1M. The next two concentrations produced very similar results.
In the second graph, this is shown too. The increase in steepness proves that as the concentration of an acid increase, the rate of reaction also increases. This is because of the “collision theory”. The theory says that particles of reactants must collide together, with sufficient force, to create a reaction. There must be enough collisions to make the reaction notable. When the concentration of the hydrochloric acid was increased, there were more particles involved in the reaction and therefore a much bigger chance for more collisions to take place. While more collisions are taking place, more energy is being made and thus increases the rate of reaction.
As my tables and graphs are adequately consistent, I am able to make a conclusion from the investigation, with confidence.
Evaluation
The apparatus used seemed satisfactory and there were no problems encountered in our experiment due to it. We used the same apparatus throughout in case there was a fault, and this therefore would have kept the fault constant and would not have affected accuracy.
The first graph generally shows the correct correlation between the time taken and the volume of the gas produced. There are some minor discrepancies however. The points plotted for 0.5M are not in a very straight formation, but a bit curved in the middle. The second graph has a good formation of points, and shows the relationship between the rate and the concentration quite well. The points, although not in a perfect straight line are generally near to the line of best fir. In general, the data collected is reliable and shows a good enough pattern to draw conclusions from.
The trends shown by the graph show that the higher the concentration of hydrochloric acid, the less time it takes to produce a certain amount of carbon dioxide gas in a reaction. The second graph shows the rate of reaction increases as the concentration does.
In the second graph the line does not go through the origin. The reason for this is human error. There may have been a time delay, when trying to put the bung onto the conical flask, start the stopwatch and record results. Another explanation is in reading the gas syringe erroneously.
If I were to do the experiment again, there would be some things I would do differently to obtain more accurate results. After adding the water to the acid, I would swirl the conical flask to mix the two substances. This would help the reaction between the marble chips and liquid start more quickly, and there would be no delay. I would also ensure that I had pushed the bung in far enough before starting the stopwatch, as this can be a hindrance to the reaction.
From my results, and the trends that I can gather from them I can come to a sensible conclusion. This is that, the time that it takes to produce a set amount of gas is less, when the concentration of the acid used in the reaction is greater. Also, the rate of reaction increases greatly, as the concentration of the acid does.
If I want to extend the investigation to justify the results further, I may try using a different acid, such as sulphuric acid, in place of hydrochloric acid. This would show whether the rate of reaction is increased when all acids’ concentrations are increased, and prove this to be a general rule, and not just with hydrochloric acid. I may also try different concentrations to see whether it still affects the rate of reaction in the same way.
