- Using the balance, measure out 2 g of medium sized marble chips. Pour the marble chips into the conical flask.
- Check that the gas syringe is at 0.
- Quickly pour the acid-water solution into the conical flask with the marble chips. Place the bung into the flask firmly as soon as you can to prevent escaping air and press the start button on the stop-clock.
- Watch the stop-clock and gas syringe and record every 30 seconds the amount of gas produced using the gas syringe. After 3 minutes, end the experiment
- Repeat this experiment for three times for each different acid concentration.
I want very accurate results so I am going to repeat my experiment three times and take an average as well as separately recording each experiment. Each time I do the experiment I am going to measure the rate of reaction at five different concentration levels at intervals of thirty seconds for three minutes so that I can demonstrate a proportional relationship between these two factors.
Fair Test
The following are variables that could affect my results and how I need to take precautions to affect them doing such:
- The temperature – I need to measure the temperature at the beginning of each experiment to ensure it is consistent. It should be approx 18 C (room temperature)
- The surface area (size of the chips) – I have chosen to use medium sized marble chips which I hope will be consistent in sizing
- Adding a catalyst (this is possible but not for this reaction)
- The mass of the carbonate (amount of chips) – I am using the same mass of chips each time (2g), which I measure on a top hand balance.
- I will also used distilled water as it is neutral and would not affect the acidity of the solution
Safety
Whilst carrying out the investigation I will of course wear safety goggles and a lab coat to protect my eyes from harmful acids. I will also stand up whilst carrying out the experiment in case I spill acid and it goes onto my lap. I will also tie my hair back and keep the work surface clear.
Preliminary Experiment
Before I did my real experiments, I carried out preliminary experiment to give me a better idea of how the experiment would shape out and to ensure I used appropriate measurements. The factors I worked out in this experiment were:
- The mass of marble chips - I tried using 6g and then 4g but found that they gave out gas too quickly to measure effectively as the gas syringe met its maximum after 1 minute or so. I settled on 2g as this meant the experiment could last for at least 3 minutes.
- The timing – I originally thought that 5 minutes would be adequate but when I realised that that I did not have time to repeat the experiment that many times then. Also, after 3 minutes or so, the experiment has ‘finished’ (in that the syringe was full) so there was little point in the extra 2 minutes so I decided to use 3 minutes instead.
- The size of marble chips – I used medium sized marble chips as I felt they were large enough to ensure a quicker reaction but not too small that the experiment would be over soon. There was also a balance of slightly larger and slightly smaller ones also.
- The measurements of acid – I had originally chosen to use 50ml of acid and when I used that I felt that it was adequate as it was deep enough to submerge the chips but also was economic with acid.
Variables
The concentration of Hydrochloric Acid you use is the independent variable because it will
vary, and the amount of gas produced is the dependent variable because it depends upon the concentration of hydrochloric acid. Other variables throughout the investigation, which will vary are the volume of water used, and the volume of hydrochloric acid. The variables which will remain unchanged are the temperature (room temperature) will stay the same in order for it to be a fair test, because if the temperature changes it will effect the rate of reaction between the reactants, either by speeding it up if the temperature rises because the particles move faster and travel a greater distance in a given time and so will be involved in more collisions. Or the temperature may slow the reaction down due to particles moving slower.
OBTAINING
In all, I conducted 3 ½ experiments. This is because half way during one experiment I realised I was getting anomalous results which had not fitted with the previous ones and I therefore restarted the experiment for which I received results that fitted appropriately with results I had previously received.
ANALYSING
Below are my results from the above table presented in graphical form. The first four present the raw data and the other two are the calculated rates of reaction.
However, my aim in this experiment was to investigate the change in the rate of the reaction and I am therefore also presenting my results showing correlation between change in concentration and rate. Rate is calculated as gas produced/time.
My results agree with my prediction, as the concentration has been increased, the rate of reaction has definitely increased. This is a pattern shown by each experiment I conducted. They show that the higher the concentration of acid, the faster the reaction.
This shows that if a solution is made more concentrated there are more particles of reactant moving amongst the water molecules, which makes collisions between the important particles more likely.
Line of Best Fit Graph
This graph shows that there is a slight anomalous result at 30 ml of hydrochloric acid. It has also been evident that this is point in all experiments where there is a larger amount of gas produced at the same points in the reaction between 25ml and 30ml of Hydrochloric acid.
However, the best-fit graph only confirms that the rate of reaction increases at a steady rate from what I can see as the concentration of Hydrochloric acid increases.
The collision theory states that if, the more concentrated the reactants, the greater the number of collisions between particles increase. This also explains why the greatest rate of reaction is usually as soon as the reactants have been mixed, i.e. they are both at their highest concentrations. As the reaction continues, the concentration of the reacting substances decreases and so does the rate of reaction. When a reaction takes place, all the particles of the reacting substances must collide with each other, and secondly a fixed amount of energy called activation energy (Ea) must be reached if the reaction is to take place. If the particles can produce the right amount of energy (i.e. if they collide fast enough and in the right direction) a reaction will take place. This experiment has proved this, as it is evident with the first graphs that the rates of reaction are faster at the beginning of the experiment than at the end as more gas is produced at the beginning.
The conclusion I have made from my results agrees with my original prediction. The (average) rate increases from 0.007407 at 10ml concentration to 0.548148 at total Hydrochloric Acid.
I calculated the rate as total gas produced divided by the time (180 seconds). This provided the average rate within the experiment or the actual rate had the experiment reacted at a steady rate throughout (which it did not).
The final chemical Equation was:
EVALUATING
I am pleased with the results I have obtained. I feel the experiment went well and the results allowed me to meet my prediction and make a conclusion as to the rate of reaction.
I believe my results are fairly accurate. The gas syringe used to measure the gas produced and therefore the reaction was an accurate way of measuring as it had an intricate scale, which providing it was read off accurately proved to give reliable results. In all of my three experiments, I have obtained extremely similar results. This is useful as I really trust the recurring pattern. The reason for these similar results would have been as the conditions were consistent i.e. temperature, equipment, marble chips. The experiment was conducted identically on each occasion also, so any gas produced before the bung was replaced in the conical flask that was lost, would be lost in every case and therefore would not affect the results anomalously.
Looking at my results, I do not think I have achieved any extremely anomalous results. In the first and third experiments however, the line of results for 50 ml concentration is not straight around 2 minutes. It falls short by only a few cm³ though so is not drastic. The pattern results are likely to change around this time though, as at two minutes into the experiment, the rate of reaction will have inevitably slowed down. I am not at all worried however, that these ‘anomalous’ results have affected my conclusions on the pattern, however it helps me to make an observation on the speed of reaction.
Although it seems problems didn’t occur, problems may have occurred during the experiment from faults in my method. For example, we used the medium marble chips, which were supposedly uniform surface area although there were big ones and small ones within that. We measured the marble chips used in mass rather than volume, which I would do in the future as the surface areas of the substance affect the rate at which it is broken down. I could also have engineered a more accurate way of beginning the experiment. Just before the stop clock was started, the marble chips were thrown into the flask containing the concentrated hydrochloric acid, which was quickly closed. Therefore, the gas produced as soon as the chips hit the acid, would have been lost and not been appropriately measured. I would change that by having a sealed flask with both the acid and chips in and the flask being shaken about and reacted in a contained environment would signal the start of the experiment. If I was carrying out this experiment in a sealed, temperature controlled laboratory, I would maintain that the temperature was exactly the same each time as when I conducted the experiment, I was satisfied that each time the temperature was roughly room temperature (18°C) whereas I would ensure it was maintained each time the experiment was conducted.
If I was to further this investigation into the rate of reaction I would do a more detailed version of this experiment. I would use larger quantities of substances (therefore a larger gas syringe) and record for a longer amount of time. I would enlist the help of technology to record the change of the gas syringe as it happens rather than ever 30 seconds, therefore plotting me the most accurate graph. Using this technique could help me investigate further how reaction rate changes within a reaction. I would change the reactants to produce different products and try different acids and different substances to investigate whether rate is similar or if it depends on the reactants involved and conditions. Within this, I could investigate using catalysts to speed up the reaction between hydrochloric acid and marble chips.