The aim of the experiment is to find out the rate of reaction at which Alka-Seltzer tablets react with water. The input variable that I will change is temperature.
State of problem
The aim of the experiment is to find out the rate of reaction at which Alka-Seltzer tablets react with water. The input variable that I will change is temperature. The output variable will be measured by the time it takes for the Alka-Seltzer tablets to dissolve.
Input variables
In this experiment there are two main factors that can affect the rate of the reaction. These key factors can change the rate of the reaction by either increasing it or decreasing it. These were considered and controlled so that they did not disrupt the success of the experiment.
Temperature- As the temperature increases, the movements of molecules also increase. This is the kinetic theory. When the temperature is increased the particles gain more energy and therefore move around faster. This gives the particles more chance with colliding with other particles and with more force.
The increase in temperature will therefore increase the rate of reaction.
As this is the variable I am measuring I will not keep the temperature constant and therefore I will be varying it.
Concentration- If the concentration of the water is increased there is more likelihood that there will be more collisions. This is because there are more water molecules in a given volume to react with the Alka-Seltzer tablets. However if there are sufficient water molecules to occupy the Alka-Seltzer tablets an increase in the water molecules will not alter the rate of the reaction and vice versa. This is because the Alka-Seltzer tablets are already working as fast as they can to react with the water.
The concentration can be increased by increasing the volume of the water used in the reaction to dissolve the Alka-Seltzer tablets in.
To control the concentration, identical quantities of water and the Alka-Seltzer tablets were used. The water volume was measured out using the same sized apparatus.
Surface area- As the surface area of the tablet is increased the rate of reaction will also increase. This is because there is more of the reactant to react with the water. If the surface area of the Alka-Seltzer tablet is bigger the water molecules have a bigger area to react with in a given time. This means that there are more particles collide more often, and this therefore increases the chance of the particles colliding with more energy to cause a reaction.
The surface area can be increased by crushing up the Alka-Seltzer tablets using a pestle and mortar. The crushed up Alka-Seltzer tablet then can be weighed to a particular amount and then just inserted into the water.
To control the surface area the same amounts of Alka-Seltzer tablets are going to be used. This is one full tablet produced by the company.
Stirring- When the reaction is taking place if you stir the mixture it will increase the rate of the reaction. This is because by stirring the rate of dissolving of the tablet is increased.
In this experiment I am not going to stir the mixture. This is because if the mixture is not evenly stirred the reaction rate changes at different speeds. This changes the overall rate of reaction and makes the results uneven and therefore inaccurate.
These are the key factors which can affect the experiment.
Output variables
The variable which I am testing is temperature. As a result (on the effect of temperature on the reaction between Alka-Seltzer tablets and water) there should be an increase in the rate of reaction. There are two things which I can measure as the rate of reaction. On e, is how long it takes for the Alka-Seltzer tablet to dissolve, and two, how much gas is given out in a given time.
In the experiment I am going to measure how long it takes for the Alka-Seltzer tablet to dissolve. I will measure how long it takes for the reaction to take place at different temperatures. As there is no electric water-bath to use, I will measure the temperature of the water at the beginning of the experiment and at the end of the experiment. I will then find the average of the temperatures. The reaction will be measured using a stop clock in seconds.
The amount of gas produced could also be measured. The gas produced will be carbon dioxide, and it could be measured using a syringe. The syringe would have to be connected to a conical flask, where the reaction will take place between the Alka-Seltzer tablet and water.
As the bubbles of gas are given off by the reaction the plunger on the syringe moves up. We can measure how much gas is produced in one minute, and therefore as we increase the temperature more gas should be given out.
Preliminary work
In the preliminary experiment done, I found out many things that I was not originally going to do. In the preliminary experiment I used a water bath. This was to prevent the temperature of the water changing too much during the experiment. I placed a small 100ml beaker into a big 350ml beaker. However, I found out that it took longer to set up the water bath, and it was difficult to place the beaker inside the water bath. I repeated this without using a water bath and I found it more efficient and easier, ...
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Preliminary work
In the preliminary experiment done, I found out many things that I was not originally going to do. In the preliminary experiment I used a water bath. This was to prevent the temperature of the water changing too much during the experiment. I placed a small 100ml beaker into a big 350ml beaker. However, I found out that it took longer to set up the water bath, and it was difficult to place the beaker inside the water bath. I repeated this without using a water bath and I found it more efficient and easier, especially due to the time span. Also, when using a water bath less replicates were done whereas doing the experiment without the water bath gave me more time to do replicates.
In the preliminary I also found out that I should use temperatures from 20oC - 90oC. This is because anything below 20oC would need freezing off the water as it is below room temperature and anything above 90oC would cause the water to start evaporating. The evaporation would change the amount of water level.
To find out how much water I should use, I tested different volumes of water with an Alka-Seltzer tablet, and timed how long the Alka-Seltzer tablet took to dissolve. The volumes of water I used were 25ml, 50ml, 75ml, and 100ml. I found out that using 25ml and 50ml of water produced a quite a slow reaction whereas a volume of 100ml produced a reaction rate nearly the same as using 75ml of water. In the end I found out that 75ml of water was the right volume of water to use, and produced a steady reaction.
To find out what temperatures to use, I experimented with temperature from 20-800C. From 600C onwards up to 800C the rate of reaction was the same. For this reason in the actual practical I will only use temperatures ranging from 20-700C.
Another point that I found out while doing the preliminary practical is that the temperature at the start of the experiment is different to the temperature at the end of the experiment. So when finding out the temperature at which the tablet dissolved was wrong. To solve the problem in my practical, I will measure the temperature at the start of the experiment and at the end of the experiment and find out the average temperature.
Below are basic results which I achieved in finding out the results for the preliminary
Results comparing different volumes of water:
Volume of water (ml)
Temperature of Beaker in (oC)
Time taken for Alka-Seltzer tablet to dissolve (s)
25
40
63
50
40
45
75
40
34
00
40
32
Results comparing stirring to not stirring:
Volume of water (ml)
Temperature of beaker (oC)
Time taken for Alka-Seltzer tablet to dissolve (s)
Stirring
75
30
34
Not Stirring
75
30
28
Pilot Experiment
Diagram
Method
Below is a basic outline of what I did:
* The apparatus was set up as in the diagram
* A measuring cylinder was filled up with 75ml of water.
* This water was then poured into a beaker.
* This beaker was placed on top of a blue flame Bunsen burner with the air hole fully opened.
* A thermometer is used to measure the water inside the beaker.
* Once the water in the beaker reached the adequate temperature, the Alka-Seltzer tablet is inserted into the beaker and simultaneously the stop clock is started.
* The beaker is then taken of the gauze and laid on the table.
* Once the Alka-Seltzer tablet had dissolved, the stop clock is stopped and the final temperature of the water inside the beaker is measured.
* This is repeated 3 more times.
(Note: when doing the experiment at room temperature, the water in the beaker is not heated, and so the Alka-Seltzer tablet is placed straight into the water.)
Results
Average temperature of water in beaker in oC (1dp)
Average time taken for Alka-Seltzer tablet to dissolve in seconds (1dp)
/time taken for Alka-Seltzer tablets to dissolve in seconds (3dp)
25
35.3
0.028
31
26.7
0.038
40
21.0
0.048
49
6.8
0.060
60
5.3
0.066
70
3.7
0.073
From the results obtained, and from the graphs, the experiment went quite well. At 60oC onwards the graph tended to curve, and this was due to the fact of the hardness in water being dissolved. The reaction also seemed to get slower and slower.
The 1/time graph was also good, and showed that 1/time was inversely proportional to time.
Background Information
The Alka-Seltzer tablet dissolves in solution. The higher the temperature the quicker the tablet dissolves in water. This is because as the temperature increases the kinetic energy of the molecules increases. This causes them to move around faster. As they move around faster they are more likely to collide with each other with more force that is more likely to produce a reaction.
They have to collide with more than a particular amount of force to break the activation energy barrier. Different reactions have different activation energies. A reaction rate will only take place if the colliding particles have more than a minimum amount of energy. This minimum amount of energy is known as the activation energy. If the activation energy is very large, only a small amount of molecules have enough energy to react. Therefore the reaction is very slow.
However if the activation energy is very low, most molecules have enough energy to react and the reaction proceeds fast. An increase in temperature gives molecules more energy and the reaction also proceeds fast.
When the Alka-Seltzer tablet is reacted with water, the reaction produces a fizzing sound, releasing a gas. The gas released is carbon dioxide. The Alka-Seltzer tablet consists of several chemicals. These include sodium bicarbonate also known as baking powder, and citric acid. When the tablet is dropped in water, the citric acid and the sodium carbonate react producing a fizz and bubbles. This fizz or bubbles shows that carbon dioxide is being produced. And a chemical reaction takes place.
Below is the equation for the reaction:
Hypothesis
As the temperature is raised, the rate of the reaction will increase. However, this is up to a certain point at which the molecules would be reacting as fast as they can.
Predictions
As the temperature increases the movement of molecules also increases as they gain more energy. This theory is based upon the kinetic theory. This also means that the rate at which the particles collide also increase. As more particles are colliding in a given time and also as the particles have more energy they collide with more force producing a reaction breaking the activation energy level. Some of the particles colliding will not break this activation energy barrier and so will not produce a reaction.
As the higher the temperature is the reaction will occur the fastest I expect the reaction to occur fastest at around 60oC or 70oC. However, after this increase in temperature I do not expect their to be an increase in the rate of reaction. This is because around this time the molecules would be reacting as fast as they can already.
I would expect the graph to like this:
I would also except to see a double in the rate of reaction as the temperature is increased by 10oC. This idea is based upon the Q10 theory.
Safety Precautions
In order to ensure safety the following must considered;
* Protective eye wear should be worn e.g. goggles to ensure that no Alka-Seltzer tablets in solution get into your eyes as it can cause allegories.
* An apron should be worn to ensure that no Alka-Seltzer tablets in solution get onto your clothes. This is because it can cause stains.
* Caution should be taken when handling hot beakers and other equipment so that there is no damage of equipment.
Fair Test
In order to ensure a fair test the following must be considered;
* The same sized apparatus is used. This is to ensure a fair test and different sized equipments can lead to unfair results.
* The same sized tablet produced by the company must be used to ensure more accuracy over the experiment and so that there is no higher amount of the reactant.
* The same volume of water must be used to ensure more accuracy over the experiment and so that there is not more concentration of water.
* The same method is used for each experiment, and the temperature is only altered.
Planned method
Apparatus:
00 Measuring Cylinder
00 Beaker
Thermometer
Bunsen Burner
Tripod
Gauze
White Mat
Stop Clock
Apron
Safety Specs
Water supply
Diagram:
Method:
For this experiment I am experimenting on how the change in temperature would affect the rate at which an Alka-Seltzer tablet dissolves in water. I will measure how long it takes for the tablet to dissolve at different temperatures.
All the apparatus is set up as shown in the above diagram. 75ml of water is poured into a 100ml measuring cylinder. This water is then poured into a 100ml beaker. The beaker is then placed on top of a gauze lying on the tripod (Note: the beaker is not placed on top of the Bunsen burner when doing the control experiment. This is because the first temperature measured, will be the room temperature. This is the temperature at which the tablet will first be placed into the beaker). After turning open the gas tap, using a lighted splint the Bunsen burner is then lit to a blue flame with the air hole opened completely. Once this is done, a thermometer and stop-clock are then taken. The thermometer is then placed into the beaker, and the temperature of the water inside the beaker is measured, reading the temperature of the thermometer at eye level. When the temperature is correct, one Alka-Seltzer tablet (The tablet is the same sized tablet supplied by the company) is placed into the beaker and simultaneously the stop watch is started. The Alka-Seltzer tablet must not have been in contact with water before. Also at this time the beaker is removed from the gauze and placed on the table. Once the tablet has dissolved the stop-watch is immediately stopped, and the final temperature inside the beaker is measured.
The average temperature is then found out using the equation:
Average temperature = The Initial temperature- The final temperature
2
This method is used to test the following temperatures:
Room
30oC
40oC
50oC
60oC
70oC
Each temperature is replicated 3 more times and the whole experiment is then repeated one more time.
Justifications For Method
* A 100ml measuring cylinder is used to measure 75ml of water as it is the most accurate. A 75ml measuring cylinder was not available by the school and so using the 100ml measuring cylinder proved to be the most accurate. A 250ml measuring cylinder would have been far too large and therefore not accurate as the space between the numberings was not very clear. Only large amount of water was used would the 250ml measuring cylinder prove successful.
* The water is not measured straight into the beaker, because the beaker is not a reliable piece of equipment for measuring amounts, as there are no clear numberings. Using a measuring cylinder would therefore ensure more accuracy.
* The air hole is opened completely so that the water inside the beaker which the flame from the Bunsen burner is heating, will heat more quickly, than a half opened air hole.
* The Alka-Seltzer tablet must not be in contact with any water before the temperature. This is because it would react with the water, and therefore it would disrupt the final result.
* The temperature of the thermometer is measured at eye level. This is because it is directly in the line of sight, so no misreading can occur.
* The experiment is replicated, so that if there was anything wrong with the final result, you would know from the replicate.
* The temperatures range from room temperature to 70oC, because after 60oC the rate of reaction does not change, as found out from the preliminary. The temperatures start of from room, because anything below that needs freezing. Normally, for a good graph 6 points are needed to plot a good graph, and that is why 6 temperatures are taken.
Safety Precautions
In order to ensure safety the following must considered;
* Protective eye wear should be worn e.g. goggles to ensure that no Alka-Seltzer tablets in solution get into your eyes as it can cause allegories.
* An apron should be worn to ensure that no Alka-Seltzer tablets in solution get onto your clothes. This is because it can cause stains.
* Caution should be taken when handling hot beakers and other equipment so that there is no damage of equipment.
Fair Test
In order to ensure a fair test the following must be considered;
* The same sized apparatus is used. This is to ensure a fair test and different sized equipments can lead to unfair results.
* The same sized tablet produced by the company must be used to ensure more accuracy over the experiment and so that there is no higher amount of the reactant.
* The same volume of water must be used to ensure more accuracy over the experiment and so that there is not more concentration of water.
* The same method is used for each experiment, and the temperature is only altered.
Method Update
Nothing was changed from the last method written.
Conclusion
The results achieved in the practical supports the hypothesis stated. As the temperature is increased the rate of reaction also increases. This is seen in the 1/time graph, where we can see that the graph is getting steeper. However this is up to a certain point at which an increase in temperature does not affect the rate of reaction.
On the 1/time graph at 60oC as you can see from the graph, the rate of reaction stays the same, and does not increase. This is not an anomalous result but merely because, as is stated in the hypothesis, because the reaction is already proceeding, as fast as it can. The molecules reacting cannot react any faster because they have the maximum amount of energy needed to react already. This is why the reaction rate is also proceeding at the same rate at 70 oC.
For the graph for time against temperature the graph is curved at the beginning but becomes straight as you go down it. This is because the hardness of the water was slightly being removed. At higher temperatures the calcium hydrogen carbonate starts to decompose. This removes the temporary hardness in water removing the dissolved calcium and magnesium ions in the water. This makes the experiment unfair because at lower temperatures the reactions would have proceeded slower as there was hardness in the water.
In my predictions I stated that I would expect a big change in the trend of the graph at around 60 oC, but because the calcium and magnesium ions only started to dissolve around this temperature, the graph would have changed in trend at later temperatures.
In my predictions I also stated that the reaction would double every time the temperature was increased by 10oC. This is the Q10 theory. From my results this was not clearly shown but I think if the apparatus was more accurate, the results would be more accurate.
However, I did see some signs of this happening.
For example:
20oC- 42.0 seconds
30oC- 26.3 seconds
In this example the rate of reaction doubles by 1.6. However this was basically the only example to show this. This was probably because temporary hardness was being removed.
Evaluation
Generally the experiment went quite well on the whole. However there were many things that could be improved. One was the equipment. Burettes could be used instead of measuring cylinders, as they are more accurate. They measure to one decimal where as measuring cylinders only measure to a whole number. This would therefore ensure more accuracy as a whole.
Also a thermostatic water bath would also ensure more accuracy over a heated beaker. This is because the water inside the water bath can be set to a particular temperature, and the water would stay to that temperature. When using a beaker to heat the water, the temperature could always change in that it could increase in temperature if heated more, or decrease in temperature, if not heated.
As you can see form the results and the graph there was an anomalous result. This could have been caused for many reasons the main being human error.
Below are points of what could have one wrong:
* If the amount of water was not measured correctly it would change the overall result. This is because too much water would cause an increase in the rate of reaction, and too less water would cause as slower reaction. To ensure more accuracy over this a burette could be used as mentioned above.
* If the Alka-Seltzer tablet was not put into the beaker at the correct temperature there would be inaccuracies in the overall result, and if the final temperature at the end of the experiment was not measured properly, it would have caused even more inaccuracies. This is because at a particular temperature the rate of reaction would be different from what it should be. To solve this problem a thermostatic water bath could be used as stated above.
* If the stop watch was stopped to early or late, again the overall reading would not be as accurate as it could have been.
* It was almost impossible to tell when the Alka-Seltzer tablet had dissolved, each time the experiment was done. This was a huge problem for the experiment as this could have totally caused problems to the experiment. This could be improved by a special type of detector apparatus, which bleeped when the correct amount of Alka-Seltzer tablet dissolved, each time the experiment was done. This would give us an extra measure of accuracy each time.