Diagram of Equipment
Method
To complete the investigation I need a clear method to tell me how to do the experiments. Below I have written a method to show how to complete the experiments needed for the investigation:
- Wear protective clothing such as goggles and a lab coat.
- Collect and arrange the equipment.
- Attach the gas syringe to the stand and clamp horizontally.
- Attach the glass tubing to the rubber bung and the other end to the gas syringe, making sure that the syringe is push to the end, reading zero.
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Using the measuring cylinder measure out 20 cm3 of hydrochloric acid, making sure not to spill any over skin.
- Then place a piece of calcium carbonate of small size on to the digital scales. Using a scalpel cut of excess amounts to make the total weight of the chip 2 grams and make all chips roughly the same size, measuring with a ruler.
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Then add the 20 cm3 of hydrochloric acid to the conical flask, making sure the rubber bung is detached from the flask.
- Quickly drop in the 2 grams of calcium carbonate and quickly close the conical flask by sealing it with the rubber bung.
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At intervals of 20, 40, 60, 80, 100, 120 seconds, which can be seen from the stopwatch, note down the amount of carbon dioxide released from the reading on the gas syringe in cm3. Note the result down in the table of results.
- Repeat the experiment for each concentration of acid. For each concentration, repeat the experiment five times to ensure reliable results, and then calculate the average time.
Safety
Many safety precautions must be taken when handling with harmful substances such as hydrochloric acid. Hydrochloric acid is a particularly dangerous substance as it is corrosive to skin, meaning that it can damage eyes, skin and tissue underneath the skin. The precautions that must be taken are stated below:
- Wear goggles, to ensure that no acid has contact with the eye. If acid comes in contact with the eye it can impair vision and cause blindness.
- Wear a lab coat to ensure that no acid is spilt over the skin. If acid comes in contact with tissue, it can cause burning and scarring.
- Wear gloves to ensure that no acid is spilt over the hands. If acid comes in contact with tissue, it can cause burning and scarring.
- Tie hair back and tuck ties into shirts to ensure that they do not affect you while conducting the practical.
- Complete all practical work standing, tucking chairs in, to ensure that in case acid is spilt, the person can move away quickly.
- Keep the scalpel away from people and while walking hold the blade pointing towards the ground.
Preliminary Results
Before completing the investigation I conducted a set of preliminary results. I decided to use a solution of 2 molar hydrochloric acid as this was the highest concentration I was using and was the only molar solution available for us to use. This also meant that I could base the other concentrations depending on these results. From the results I can see that they were reliable, which shows the method that was used is accurate and produced dependable results. Also by considering the time taken to complete an experiment for one concentration, I decided to investigate further concentrations ranging from 0.25 molar to 2 molar, at intervals of 0.25 molar. This helped to make the overall reliability and conclusion of the investigation accurate.
While conducting the preliminary experiment, we faced a few problems. One main problem was that different molar solutions were not provided. This meant that we had to make our own molar solutions from a basis of 2 molar hydrochloric acid. We had decreased the molarity by adding different volumes of distilled water. Below shows a table of the volumes used to make the different solutions:
We had used simple mathematics to lower the molarity of the solutions, using proportion. Below I have shown an example of the calculations I have used to work out the molarity of solutions:
To make an accurate solution we needed exact amounts of hydrochloric acid and distilled water. To do this we had to add a few items to the equipment list, which are listed below:
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Distilled Water - To use to decrease the molarity of the hydrochloric acid solutions.
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Pipette - To measure accurate amounts of distilled water and hydrochloric acid while making different molar solutions.
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Glass Rod - To stir the solution to evenly spread the two different solutions.
While conducting the preliminary experiment we faced a few difficulties. These were:
- While inserting the rubber bung the gas syringe reading jumped – increasing the reading. This was due to the increase in pressure while inserting the bung. This meant that we had to minus a result (the amount increased while inserting the bung) after recording the results. We had no solution to this problem so we continuously had to minus the reading.
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While measuring out the different concentrations, the measuring cylinder used started at a reading on 10ml. This meant that we had to make large bulks of each concentration - 100cm3 instead of the 20 cm3 that we had to use for the experiment.
- While measuring out the solutions of hydrochloric acid and distilled water we measured until the bottom of the meniscus was aligned to the reading, meaning that the results would be reliable.
- While collecting the data we were provided with different types of gas syringes. As different gas syringes were used, it caused a variance in our results. This meant that some results had to be eliminated due to the high variance between other results. This meant that we had taken longer time than needed as some results needed to be repeated.
- Additionally I decided to use large sized chips as by having a larger surface area per chip, the overall surface area would be the same. Also I decided to use three chips that weighed to 2 grams. This meant that the average weight would be similar. This would keep the variables in control.
- I have noticed that there is a difference of results from my preliminary results and my final results. I have concluded this change to the difference in size of the conical flask. As we had used a large sized flask it meant that less gas was measured in the syringe due to gas being trapped at the top of the conical flask. This meant the preliminary results that we got were slightly lower than expected.
Before I begun my final investigation I made a few changes to my method. These changes were:
- I started measuring the levels of solutions at the bottom level of the meniscus.
- Used more marble chips so the average surface area per chip was similar.
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Measured each molar solution to 100cm3 instead of 20cm3.
Once I had completed the preliminary experiments, I conducted my final investigation with the changes I have made from my preliminary experiment. I have shown a table of results below and have shown these results through a graphical representation.
Final Results
This is a table with all our results that we had collected:
The results highlighted in yellow shows all outliers. These results were not included in the graphical representation of data.
Conclusion
I have created a graph from the results that I have collected. From this graph I can see a significant rise in the volume of gas as the molarity of the hydrochloric acid solution increased. As we increased the molarity of the solution from 0.25 molar to 2 molar, at increases of 0.25 molar the total amount of carbon dioxide produced increased.
In connection to scientific knowledge behind rates of reaction there are five factors which influence the rate of a reaction. These are:
- Temperature
- Concentration
- Surface Area
- Use of Catalyst
- Pressure
Temperature
The temperature can influence the rate of a reaction. As the temperature is raised, the particles become more charged, as they have higher amounts of energy. Once free, the particles are more likely to collide with each other, forming more new molecules and making the rate of reaction faster. When the temperature is lowered, the particles become less charged and move around slower. This means that fewer reactions are likely to take place, concluding that a decrease is rate of reactions is a result of lowered temperature.
Concentration
The concentration can influence the rate of a reaction. As the concentration increases, it means that there is more of a substance for the particles to react with. This means that there is a greater chance that the particles will collide, which speeds up the rate of a reaction. If the concentration is decreased, then there is less of the chemical, which means that fewer collisions will occur, concluding that a decrease in concentration levels slows down the rate of a reaction.
Surface Area
The surface area can influence the rate of a reaction. If the substance is broken down into several small parts, such as powder form magnesium it increases the surface area. This means that there is more area for the particles to collide against, meaning that collisions are more likely to occur, increasing the rate of reactions. If the substance is left as a large block, such as calcium carbonate (marble) chips there is less surface area. This means that there is less chance of the particles colliding, meaning that the rate of reaction decreases.
Use of Catalyst
The use of a catalyst can influence the rate of a reaction. A catalyst is a substance that speeds up a chemical reaction, but does not undergo any change. The catalyst speeds up the rate of reaction as it allows for more collisions to occur.
Pressure
The pressure can influence the rate of a reaction. The pressure mainly affects the gases in a chemical reaction. One the pressure is increased; gases have less space in which they can move around freely. This means that the particles are more likely to collide with each other, increasing the rate of a reaction. In comparison, once the pressure is decreased, it means that there is more space for the particles to move around, meaning that it is less likely for particles to collide, slowing down the rate of a reaction.
All the factors above are linked with The Collision Theory. The Collision Theory is a theory proposed by Max Trautz and William Lewis in 1916 and 1918. The rate of reaction depends on how often and with how much energy two particles collide. The collision theory outlines that a chemical reaction can only occur between particles when they collide with enough energy, so that previous bonds can be broken while new bonds form - creating new molecules.
In connection with the results I have collected - as I increased the molarity of the hydrochloric acid solution, it meant that there where more hydrogen and chloride particles. As there where more hydrogen and chlorine particles, there were more chances of reaction between these particles and the calcium carbonate molecules. The more reactions means the quicker the reactants are produced. This is shown in the graph through the increased production of carbon dioxide. This is shown in the graph – at 120 seconds the 1 molar acid produced about 37ml of carbon dioxide whereas with the 2 molar acid it produced 91ml of carbon dioxide at 120 seconds. The increase in production of carbon dioxide is a result of more hydrogen and chloride molecules in the 2 molar solution than in the 1 molar solution.
From interpreting the diagram above, we can see that there are more HCl molecules in the 2 molar solution than in the 1 molar solution which has been diluted with water. In connection to the ‘Collision Theory’ the rate of a reaction increases with more reacting particles. As the concentration increase in the hydrochloric acid solutions, there were more HCl molecules. This meant that there were more chances of the calcium carbonate molecules reacting with the HCl molecules. This meant that more calcium carbonate reacted with the HCl in the high molarity solutions and therefore produced more carbon dioxide gas quickly – the rate of the reaction increased.
In connection to the graphs we can see significant changes in the production of carbon dioxide as the molarity of the solution increased. We can see a much steeper curve as the molarity of the solutions is increased. From the graph we can see that with the 2 molar solutions, at 100 seconds it produced on average 80.5ml of CO2, whereas with the 1 molar solution at 100 second it produced 31.2ml of CO2. From this I can conclude that as the concentration of hydrochloric acid increases, the more carbon dioxide is produced within certain intervals of time. This shows that the steeper the gradient of the slope, the faster the reaction.
Additionally I have calculated the gradient for each molar solution. I have calculated the gradient of each line by using the following formula:
By working out the formula I could get an accurate idea of the rate of reaction. From the results I can see that as the molarity of solution increased, the gradient of the graph also increased. The gradient also has indicated how much carbon dioxide gas is released every second. In connection to the results, the gradient for 2 molar solution is 0.7125 and the gradient for 1 molar solution is 0.295. This shows that once the concentration of the hydrochloric acid is increased, the gradient also increases. The gradient indicates the speed of the reaction - therefore the higher the concentration, the quicker the rate of reaction. This is linked to the collision theory - as the concentration increases there are more acid particles in the same volume. This means that there are more chances of collisions between the particles, increasing the rate of reaction. Additionally the gradient of the line shows me the amount of carbon dioxide released every second. From the graph I can see that with the 2 molar solution 0.7125ml of carbon dioxide was released every second and with the 1 molar solution, 0.295ml of carbon dioxide was released every second. As the amount of carbon dioxide released each second shows me the rate of reaction, I can come to a conclusion at as the concentration increases, the rate of reaction increases.
To come to a reliable conclusion I have worked out the average amount of carbon dioxide released each second. To work out the average time I have used the following formula:
The table below shows the amount of gas produced each second for each molar solution:
By working out the amount of carbon dioxide produced each second it indicates the rate of reaction. From the results I can see that the 2 molar solution produced 0.760ml per second, and the 1 molar solution produced 0.307ml per second. From this I can conclude that once the concentration increased, more carbon dioxide gas was being produced each second. This shows that as the concentration increased, the rate of reaction also increased.
Additionally in referral to the graph I can see that the curve of the graph is increasing but curving down (blunting) towards the level of 120 second. This is because the rate of reaction shown from the slope is steady. From the graph I can see that the 2 molar acid is blunting more sharply that the 1 molar acid. This indicates that over time, each curve for each molar solution would blunt and plateau if each reaction was allowed to react over a long period of time.
In conclusion, from the results I have collected, the graphs I have drawn and the mathematical calculations I have completed I can conclude that as I increase the concentration of the hydrochloric acid, the rate of reaction increases. This shows that the rate of reaction is affected by concentration - that increased concentration would increase the rate of a reaction.
Evaluation
During the course of completing the investigation I had faced a few problems.
One of the main problems I had faced was that while inserting the bung, pressure built up inside the conical flask which meant that the reading on the gas syringe increased. This meant that while inserting the bung I had to read how much the gas syringe increased by. Due to this I continuously had to minus the reading from my results. This may mean that I may have got slightly inaccurate results as the reading my not have been perfect - which may have impacted on my final results. I could not find a solution to this problem as every time the bung was inserted the reading on the gas syringe increased. If I was to repeat the experiment I would use a data logging system to record the amount of gas produced. By using a data logging system it would record the amount of gas produced accurately as the system would be connected to the computer which record the results. Additionally I could have tried to use a beehive case, rubber tubing and a measuring cylinder to measure the gas produced over water. This method may mean that while inserting the bung the gas levels would not increase, which can help in collecting reliable results.
In connection to my results, I had three full sets of outliers and one single outlier. I believe that the outliers were due to difficulty in measuring the amount of gas produced. This could have been due to human error in reading the result on the gas reading. Another reason could have been misreading the amount that the gas reading increased by while inserting the bung. Additionally the use of different sized conical flasks could have also lead to inaccurate results as a bigger size may have trapped more gas and lead to a decreased reading. The outlier results could have been prevented by using a data logging system or a beehive case to measure the gas produced, as describe above. Additionally these outlier results could have been made by not controlling the variable correctly.
If I was to repeat the investigation again, there are few aspects I would change which will help in making my results accurate. Firstly to make the results accurate I would need to press the timer, drop the calcium carbonate chips and insert the bung within a short period of time. This was difficult to do with one pair of hands. This may have caused inaccurate results as the calcium carbonate chips and timer may not have been pressed at the same time, which could have altered my results. Also while inserting the bung some of the carbon dioxide produced may have escaped. This may have caused my results to be slightly inaccurate. Additionally while measuring the calcium carbonate chips, I had only used scales which were to one decimal place. This means that the variable was not under accurate control, which can cause my results to slightly differ. Also although large sized chips where used, the surface area of the chips was not accurate per investigation. If I was to repeat the experiment I would use either smaller sized or medium sized chips. This would mean that the average surface area per chip would be similar, so therefore the variable would be under control. This would help in decreasing all variance between results, and help me gain accurate results. In addition I the measuring cylinder used was only to a whole number. This again may mean that the molarity and amounts of solutions may not be accurate, which may have led to inaccurate results. To overcome this problem I should have used a more accurate measuring cylinder, which may be made available to me by the science technicians. Additionally the scale on the gas syringe was only to a whole number. This again may have produced slightly inaccurate results. To overcome this problem I could have used a data logging system. Also while measuring the different solutes while making the different molarity solutions I had measuring the solutions to the bottom of the meniscus. This was not accurate as human error may have caused slight variance in measuring the solutions. Additionally when making the different molar solutions I had used tap water to decrease the molarity. As the water is not distilled it may not be pure and contain some impurities. This can again make inaccurate solutions of hydrochloric acid. In connection, while stirring the two solutions I used a glass rod. This may not have spread the concentration evenly as some areas of the acid may be more concentrated than others. To overcome this problem I would have used a magnetic stirrer, which would evenly spread the concentration of the solutions.
To work out how accurate my results were I worked out the variance of my results. I had calculated the variance using the formula below:
In relation to the variance of my results I can see that most of the variances are below 20% and the average variance is 16.29%.This show that the results I have collected are reliable.
In connection as seen from the graphs, my range bars are relatively small in size. This shows that my results are accurate and that I have made reliable
Additionally if I was to complete the experiment again I would complete more sets of results. This would help me getting a lower variance which means that my results are highly accurate and reliable. I can prove that my range bars are small as the highest range is 4 (2 Molar and 1.5 Molar), which is relatively low.
If I was to complete the investigation again I would complete all the changes above. These changes would help in controlling all variables (surface area and weight of calcium carbonate chips, amount of hydrochloric acid used and temperature), help vary my independent variable (concentration of hydrochloric acid) and help measure my dependant variable (gas produced in time). I strongly believe if I was to complete the investigation with these changes I would achieve very accurate and reliable results which can help me draw precise conclusions.
To draw a strengthened conclusion I would complete the experiment again with different solid and liquid reactants. This would help me prove whether the concentration affects the rate of reaction as other reactants may behave differently. By investigating other reactants, the results would help me prove whether the concentration affects the rate of reaction in other reactants other than calcium carbonate and hydrochloric acid. An example of another experiment I would conduct is the reaction between magnesium strips and sulphuric acid. Additionally I can continue with the experiment and test the hydrochloric acid with other compounds, or additionally I can conduct a reaction between calcium carbonate and other liquid solutes such as nitric, sulphuric and citric acid. By completing an experiment with other reactants it will help me come to an accurate and strengthened conclusion in deciding whether the concentration affects the rate of a reaction.
