Chemistry Coursework - Marble and Acid Experiment
Chemistry Coursework
Marble and Acid Experiment
Aim:
To investigate one factor that effects the rate of reaction between marble chips (calcium carbonate) and dilute hydrochloric acid.
Marble Chips (calcium carbonate) + Hydrochloric Acid
Calcium Chloride + Water + Carbon Dioxide
CaCO3 + 2HCl
CaCl2 + H2O + CO2
Variables:
To alter the rate of reaction between Marble chips and hydrochloric acid, there are a few alterations that could be made.
> Pressure- The greater the pressure of a gas the faster a reaction will occur. This is due the fact that there area greater number of particles in a given volume to react.
> Temperature- if the temperature was raised the experiment would react faster as the particles would be moving faster with more energy.
> Concentration- the concentration of the hydrochloric acid could be lowered by adding different amounts of water. This would slow down the reaction because there are fewer particles in a given volume to react.
> Catalyst- these change the rate by providing an alternative reaction pathway along which the reaction can occur.
> Surface Area- the surface area of the marble chips can be altered by changing their size. Smaller chips of the same mass will have a larger surface area. A larger surface area speeds up the reaction process, as there is a larger surface area to react at any one time.
Altering the pressure is simply not possible, as we do not posses the equipment to do this. Changing the temperature of the experiment is not a good variable as in the classroom environment; it is very hard to make the experiment a fair test with the equipment available to us. Catalysts are not available for use in this experiment. It is possible to alter the surface area of the chips but the problem lies in the fact that all of the chips vary in size and so you could never measure the differences in surface areas.
Due to this I have decided to alter the concentration in my experiment. This is not only due to the problems involving other variables but it is also possible to receive clear, accurate results when altering the concentration.
Fair Test:
To ensure accurate results we must ensure that we have a fair test. This means that each testing must be made to be identical to the last bar the variable we shall be altering. In each experiment, the same amount of Marble Chips (5g) and water to be displaced (100 cm3) must be used.
Also to ensure a fair test, we shall use the same equipment for each test and the experiments will be done in the same room at close intervals to ensure that the temperature for each is as close as possible ...
This is a preview of the whole essay
Fair Test:
To ensure accurate results we must ensure that we have a fair test. This means that each testing must be made to be identical to the last bar the variable we shall be altering. In each experiment, the same amount of Marble Chips (5g) and water to be displaced (100 cm3) must be used.
Also to ensure a fair test, we shall use the same equipment for each test and the experiments will be done in the same room at close intervals to ensure that the temperature for each is as close as possible to the last.
My variable in the experiment is the concentration of the hydrochloric acid. The volume of which must equal 50 cm3. The hydrochloric acid begins at 2 molar and so we shall decrease this at regular intervals of 0.25 my adding water. For example to achieve 1.75 molar, 43.75cm3 of hydrochloric acid would be mixed with 6.25 cm3.
Method:
Apparatus
Conical flask with rubber hosed outlet
Bee Hive shelf
Bung
Measuring cylinder x 2
Water bath
Hydrochloric Acid
Marble Chips
Water
The experiment will be set up as follows:
> The beehive shelf shall be placed upside down in the water bath, which will be filled so as just to submerge the hole in the bottom of the beehive shelf.
> One measuring single will be filled with water then flipped upside down and submerged in the bath whilst retaining the water. The glass slide can be used to assist in this difficult process.
> The rubber tubing of the conical flask is fed though the entrance of the beehive.
> The correct measurements of water and hydrochloric acid are measured out, using the second measuring cylinder and mixed together.
> Ten grams of marble chips are placed in the conical flask, the hydrochloric acid is added and the bung placed on the top of the conical flask, this must all be done swiftly to avoid gas loss.
> When the bung is in place, a stopwatch should start and measure how many seconds the bubbles take to displace 100cm3 of water.
Below is what is should look like:
The first experiment shall use 50cm3 and no water. The second shall use 40cm3 and 10cm3 of water and the amount of hydrochloric acid will decrease by 10cm3 until 10cm3.
Experiment Ranges:
We shall carry out the experiment 5 times. Using concentration levels of 2 molar down to one molar with integers of 0.4 molar (2, 1.6, 1.2, 0.8, 0.4 Molar). Each one of these experiments will be carried out three times to ensure that we receive true results. An average of the three results will be taken and anomalous results will be ignored.
Safety:
The hydrochloric acid being used in this experiment can be harmful to humans when mishandled. To protect us from any dangers, lab coats will be worn at all times as well as goggles to protect us from and drops entering our eyes. If any solution is spilt onto us then we must wash our hands immediately as the acid is corrosive and could cause us harm if we fail to do so.
Pilot Study:
A pilot study took place before the main experiment so that we can adjust our method to receive optimum results. We originally planned to count bubbles but found that this was too tricky, due to their speed, and inaccurate, due to their varying size, and so decided to measure displacement instead. The air travelled through the apparatus at a good speed and effectively
Prediction:
My prediction is that when the concentration of the acid is higher, the reaction will take place faster. This will mean that the 100cm3 of water will be displaced in less time than with a lower concentration. My reason behind this prediction is simple. With a higher concentration there are more hydrochloric acid particles to react and so collisions will be more often than when the concentration is lowered.
I predict that the ratio of concentration to time will always stay the same that means that if the molar is o.8 molar then the time will be half that of for 1.6 molar.
I predict that the graph of results will look something like this:
From my predictive graph it is easy to see that there is a negative correlation. The higher the concentration, the faster the displacement of 100cm3 of water. The lower the concentration, the slower the displacement takes place.
The gas given off by the experiment is carbon dioxide. This can be proved by the formula:
Carbonate + Acid
Salt + Water + Carbon Dioxide
Marble Chips (calcium carbonate) + Hydrochloric Acid
Calcium Chloride + Water + Carbon Dioxide
CaCO3 + 2HCl
CaCl2 + H2O + CO2
Observations:
I have 3 anomalies that I have put in italics. These results may be like this due to a number of reasons such a miscalculation in measurementsor simply a fluke result of particles meeting more or less often. I have removed these results from the averages to stop them from affecting my end results.
Below is a graph plotting all three results for each concentration against time taken:
I also wish to plot rate of reaction against molarity:
Analysis:
I have found that the concentration of the acid directly affects the time the chips take to produce 100cm3 of carbon dioxide. Unlike my preiction however, the doubling of concentration did not double the rate of the reaction.
My results prove my prediction to be correct. I knew this would be the case because there are more atoms in a higher concentrated solution to meet with marble chip atoms and so they will meet more often causeing the reaction to take place faster.. If there are less particles in the solution then collisions will be less frequent slowing down the rate.of reaction.
I said that the reaction rate would double between 0.8 and 1.6 molar; it hasn't done this. At 1.6 Molar, water in the gas cylinder was displaced in 28.71 seconds; at 0.8 Molar it was displaced in 67.55 seconds, This is roughly 9 seconds off m prediction being correct. This does not mean, however, that my prediction is wrong. It could well be down to some experimental errors such as wrongly weighing out marble chips, wrongly measuring out water or acid. The acid not being exactly 2 molar. The bung not being placed on fast enough and gas being lost at the very beginning.
Evaluation:
I think my experiment went very well. My repeats on my graph all have a similar shape showing that I conducted accuracy throughout. I also only have 4 anomalies out of 21, and only one that is grossly out, these are all ringed on my graph. Three of the anomalies are found on my last repeat, this is because I was rushing to the finish the experiment so I didn't spend as much time trying to get the accurate amount of Hydrochloric acid/water or marble chips. If I hadn't poured or weighed out an exact amount I wouldn't bother to rectify it because I had little time and wanted to finish the experiment in time. My other anomaly is in my first experiment but it is only slightly out I think this is because, I didn't stop the stop watch as instantaneously as I should of done or I lost some Carbon Dioxide at the beginning as I didn't put the stopper on the conical flask as fast as I should have.
In future so that I don't get any inaccuracy's I will not rush at the end even if I am running out of time, I will still weigh/pour out the accurate results and if it is not exact the first time I will rectify it until it is. I will make sure my responses are more accurate to putting on stoppers and stopping stopwatches.
This experiment is very reliable, the lines of best fit for the repeats are very close, at some points I found the graph quite confusing to plot because they were very close to one another and sometimes over crossed each other. I think that the results I obtained were sufficient enough to draw a firm conclusion because any anomalies, I beleive were caused by experimental errors caused by me.
Duncan Fisher