pH:
HCL is a acid that in aqueous solution which can split into H+(aq) and Cl-(ag). pH stands for potentiometric hydrogen ion concentration so the concentration of H+(aq) determines the pH of the aqueous solution. In this case HCL is an acid because it has free H+. The concentration of HCL is determined by the concentration of H+(aq). The higher the concentration of H+(aq) in solution the higher the morality of the hydrochloric acid. For example 2m HCL will have more H+(aq) than 0.2M HCL.
I decided to test concentration and change the concentration of the solution that I put the agar in and time the time in which it takes for the agar to go from pink to clear.
For preliminary I will do: 0m, 0.2m, 0.4m, 0.6m, 0.8m, 1m, 1.2m, 1.4m, 1.6m, 1.8m and 2m.
For final experiment I will do: 0m, 0.1m, 0.2m, 0.3m, 0.4m, 0.5m, 0.6m, 0.7m, 0.8m, 0.9m, 1m, 1.1m, 1.2m, 1.3m, 1.4m, 1.5m, 1.6m, 1.7m, 1.8m, 1.9m and 2m.
Variables
I will be changing the concentration of hydrochloric acid to produce a range of results to show how the time differs as the concentration of hydrochloric acid increases. This will be done by measuring different volumes of hydrochloric acid as I have shown in the section: how to make concentrations.
I will be keeping the person watching the reaction constant, to make the experiment and the results reliable as different people may observe differently to each other producing varied results, therefore the results will be more reliable.
Also the volume of the solution must be kept the same, this is because if I change it my results would vary as the increase in volume will contain more atoms of hydrochloric acid, making the agar neutralize faster.
The size of the agar cubes will also be kept the same, because this will make the experiment fair. Furthermore the increase in the size of the agar, the longer the rate of reaction will take as there is more sodium carbonate for the hydrochloric acid to react with.
Preliminary
Predications
From what I have discussed in my introduction, if the change in concentration is increased this will result in more particles in the same volume, thus there are more collisions. Due to this I think that the higher the concentration of hydrochloric acid the shorter the time it will take for the agar to go clear. Collision theory states concentration increase will lead to there being more particles of acid available for reaction with the agar/NaCO3 particles so there are more reactions therefore the agar goes clear faster.
Equipment
- Agar- to measure the rate of reaction from the pink turning clear.
- Beakers-to collect the hydrochloric acid and distilled water.
- Boiling tubes- to put the solution and agar.
- Distilled water-to change the concentration of the solution.
- Hydrochloric acid-for the concentration of the solution
- Measuring Cylinders- to measure the hydrochloric acid and distilled water with and make the measurements accurate.
- Test Tube Racks- to hold the test tubes.
- Scalpel- to cut the agar.
- Tile-to cut the agar.
- Stop Clock-to time the rate of reaction.
- Ruler- to measure the 1cm by 1cm cubes.
Method
- Collect equipment
- Measure the hydrochloric acid and/or distilled water (according to table below)
- Pour into boiling tubes
-
Cut the agar (how is the agar made: 2g of agar in 100cm3 H20 add 10cm3 of 0.2Mol dm3 NaCO3 + 5cm3 phenolphthalein) into equal cubes of 1cm by 1cm
- Put the agar cubes into concentrated solution
- Start stop clock
- When agar goes clear stop clock
- Record time
- Repeat the procedure for all concentrations.
How to make concentrations
Results
Conclusion
I found that the lower the concentration, the longer the reaction will take but I also found that 0m did not turn clear this is because the are no hydrochloric acid particles to collide with the sodium carbonate so the agar will not neutralize to make the agar go clear rather it will stay pink. I found that my prediction was right so as the concentration increases, the increase in the atoms colliding decrease the time it takes in which the agar neutralizes the agar and that the technique I used made my result more accurate. I will be making the following changes to my method and equipment:
Firstly, I will use a collaborated pipette instead of a measuring cylinder to make my results more accurate and this will ensure that a precise amount of water is added, so this is a more accurate way of measuring solutions.
Secondly, I will increase the range to see more of a change so instead of 10 results I’ll do 20 results.
These changes will make my result more reliable and my technique more accurate; the rest equipment will stay the same because as I found in my preliminary they were accurate with their usage. The method will also remain the same as it produced reliable results.
Final experiment
Predications
From what I have discussed in my introduction, if the change in concentration is increased this will result in more particles in the same volume, thus there are more collisions. Due to this I think that the higher the concentration of hydrochloric acid the shorter the time it will take for the agar to go clear. Collision theory states concentration increase will lead to there being more particles of acid available for reaction with the agar/NaCO3 particles so there are more reactions therefore the agar goes clear faster.
Equipment
- Agar- to measure the rate of reaction from the pink turning clear.
- Beakers-to collect the hydrochloric acid and distilled water.
- Boiling tubes- to put the solution and agar.
- Distilled water-to change the concentration of the solution
- Hydrochloric acid-for the concentration of the solution
- Collaborated Pipette- to measure the hydrochloric acid and distilled water with and make the measurements accurate.
- Test Tube Racks- to hold the test tubes.
- Scalpel- to cut the agar.
- Tile-to cut the agar.
- Stop Clock-to time the rate of reaction.
- Ruler- to measure the 1cm by 1cm cubes.
Method
- Collect equipment
- Measure the hydrochloric acid and/or distilled water with a collaborated pipette (according to table below);
- Pour in boiling tubes;
- Cut the agar into equal cubes of 1cm by 1cm;
- Put the agar cubes into concentrated solution;
- Start stop clock;
- When agar goes clear stop clock;
- Record time;
- Repeat procedure for all concentrations.
How to make concentrations
Results
Conclusion
The graph illustrates a negative correlation between the concentration of hydrochloric acid and the time in which it took for the agar to go clear, indicating that as the concentration of hydrochloric acid is increasing the time in which it take for sodium carbonate atoms to react with the hydrochloric acid atoms to make the agar go clear/neutralize the agar is decreasing, this is because in high concentrations of HCL there are more H+(aq) available to react with the CO 3 (aq) in neutralisation like I had mentioned in my introduction. This is the equation of the experiment:
2HCL(aq) + NaCO 3 (aq) → 2NaCl(aq) + CO 2 (g) + H 20 (l)
Also from my graph I can estimate points which I have not tested for. For example 1.325 will approximately take 8.3min; this is based on the readings from my line of best fit.
I have also produced a comparison graph which compares my preliminary to my final results from it I can see the lines of best fit are parallel, this is because I had used 10ml of concentration in my preliminary tests and 20ml in my final experiment. Furthermore I found that my final experiment has a stronger negative correlation than my preliminary this is due to the improvements I had made like using a calibrated pipette instead of a measuring cylinder.
My result have confirmed my predication and that as the concentration of the hydrochloric acid increased, the number of atoms colliding with the sodium carbonate atoms increased making the agar neutralize faster.
I found out that at 2M the time it took an average of 4.526min as there is a high concentration of hydrochloric acid in the test tube and as the collision theory states the increase in collisions between atoms will increase the rate of reaction. I found that the lower the concentrations of hydrochloric acid the longer the time for the agar to go clear. For example at 0.2m it took 13.35min.
The cube sizes of the agar and volume of the concentration were the same in all of the tests but the time decreased as I increased the hydrochloric acid concentration. This is because as I increased the hydrochloric acid concentration, I decreased the water concentration so the collision rate increases in time
The gradient tells us how quickly the reaction was going at that time so the steeper the slope the faster the reaction. The graph illustrates that as the hydrochloric acid concentration increases the gradient becomes less steep indicating a decrease in the rate of reaction. My error bars are very small showing that my technique was accurate.
Evaluation of data
My results were quite reliable because all three repeats on each concentration were similar for example: 1.9M > 5.18, 5.19, 5.19. The results were accurate as the average difference within each concentration was 0.45 minutes. I have produced a scatter graph to show the time increase with the concentration decrease. My graph illustrates that there are no anomalous results.
My results table show that, when the dilute water was increased the time in which the agar takes to go clear increased. As I mentioned in the conclusion in the preliminary the 0m has an infinity time load to go clear this is because there are no acid particles for the sodium carbonate to collide with so the agar will not turn clear. The average time increase of the agar going clear was As you can see the molar increase causes the atoms to collide more often and faster this is why the 2m was the quickest time and the more dilute it becomes the longer the time period in which the agar turns clear. All my results are within the line of best fit. The gradient of the graph was -1.5 showing how quickly the reaction was going.
Evaluation of Procedure
I believe my method was fairly accurate and I had measured the size of the agar cubes and the volume of the hydrochloric acid and dilute water correctly (as it had said in my method) by going down to table level and checking if it was exactly at the right measurement and using a calibrated pipette which is an accurate piece of equipment. I had also used suitable equipment, which I had decided after my preliminary experiment to see which equipment was suitable and kept the person who was watching the agar clear the same this is to make the result reliable as different people may observe differently to each other producing varied results. Also the fact that I had measured to two decimal places and used a digital stop clock contributed to producing reliable results. I have used a wide range to identify the marginal increases within them.
I could have improved by using accurate way of cutting the agar into identical pieces I would as this could also have affect my result. Finally the person watching the agar go clear cannot be a 100% accurate so a device to exactly identify when it goes clear could have improved my results this could be a light- intensity meter with a stop clock which would stop as soon as it goes clear or I could use a speed camera and go over the film on the computer and identify were it goes clear. The sharpness of the scalpel could also have influenced my results, as the scalpel could have been slightly blunt therefore making dips and peeks on the edges of the agar.
The techniques I had used had made my data reliable, which also shows that the technique was accurate.