August 28, 2018
The Relationship Between Temperature and the Rate of Reaction
In order to study the effect of temperature of the rate of a chemical reaction, the reaction between sodium thiosulphate (Na2S2O3) and dilute hydrochloric acid (HCL) can be used.
Na2S2O3(aq) + 2HCl(aq) ? 2NaCl(aq) + SO2(aq) + H2O(l) + S(s)
Within this reaction, a precipitate of sulfur is produced. To know the relationship between the temperature and the rate of reaction, this precipitate can be used to estimate the rate of reaction when the temperature of one chemical changes while other variables are kept constant.
The independent variable will be the varying temperatures of the chemical Na2S2O3.
The dependent variable will be the duration of the reaction to occur. This will be measured by placing a cross below the reaction and time how long it takes for the cross to disappear from sight due the precipitation of sulfur using a stopwatch.
Volume of Na2S2O3 and HCL
In order to conduct a fair experiment, the volume for each of the solutions should be the same throughout. This is because one experiment will have more or less reactants compared to another experiment. Which, consequently, would enhance the speed for the precipitation to occur and thus would cover up the cross faster. Therefore, the results will not be accurate or precise.
Concentration of the Solutions
The concentration for both of the solutions will be constant. This is because solutions with higher concentrations will have faster rate of reaction, as the particles are more compacted so the collisions occur more frequently. Therefore, if the concentrations are not constant throughout the experiment, it will highly affect the result of the rate of reaction.
The cross will be drawn on a white piece of paper, which will be used for every single experiment. This is because depending of the thickness and the darkness of the cross; the reaction will need to occur longer or shorter for it to disappear. Thus, making the results to vary.
Size of the Beaker
The same size of the beaker should be used. This is because, depending on how big or small the beaker is, the total volume of the reaction would either be shallow or deep, which will interfere with the intensity of the precipitate and affect how the person views it. Thus, it would need more or less time for the reaction to react in order to cover of the cross.
Distance Between the Eye from the Cross
The distance between the human’s eyes and the cross should remain equal, as it will influence how they would view the cross. Therefore, in order to maintain the distance as much as possible, the same person should watch the cross throughout the whole experiment.
2 Beakers (100cm3)
A 10cm3 Measuring Cylinder
A 100cm3 Measuring Cylinder
A White Paper ; Pen
350cm3 of 0.025mol dm-3 Sodium Thiosulphate Solution
35cm3 of 2.00mol dm-3 Hydrochloric Acid
A Bucket of Ice with water
Heating Equipment (Bunsen Burner, matches, gauze, triangle stand, heat protectant gloves)
Due to the usage of Bunsen burner and flame, this experiment contains a potential hazard as it may burn if the safety precautions are not followed.
The hydrochloric acid with the concentration of 2.00mol dm-3 and the sodium thiosulphate solution with the concentration of 0.025mol dm-3 are both irritants
The product sulfur dioxide is toxic especially to asthmatic patients as it can trigger asthma attacks when breathed in.
When lighting up the Bunsen burner to heat up the sodium thiosulphate solution, make sure to follow the safety procedure. Such as, adjusting the Bunsen burner correctly before lighting it up. As well as, changing the Bunsen burner into ‘safety flame’ (orange flame) when not using it.
For hydrochloric acid and sodium thiosulphate solution, gloves are not required to be worn as they are just irritants. However, when they come contact with the skin, the area should be washed with water immediately.
For sulfuric acid, direct inhale should be avoided as it is toxic. As the acid also triggers asthma attacks, people with asthma should not be the person recording data directly above the reaction. If crucial, wearing a mask is possible
Lab coats, goggles, etc. should be worn for safety all times.
50 cm3 of thiosulphate solution was poured into the beaker using the 100 cm3 measuring cylinder and took the temperature using a thermometer.
A small cross was drawn on a piece of paper and was placed under the beaker.
5 cm3 of hydrochloric acid was measured into the 10 cm3 measuring cylinder.
When ready, the acid was poured into the beaker. At the same time, the stopwatch was started.
Then, the time it took for the cross to disappear when looked at from above was recorded.
The beaker was then washed and dried thoroughly.
Steps 1~6 was repeated 5 times while changing the temperature of the thiosulphate solution by heating it carefully using a Bunsen burner.
Steps 1~6 was again repeated just once more however cooling the temperature by placing the thiosulphate into an ice bucket.
Data Collection / Data Processing
When the hydrochloric acid was added to the thiosulphate solution, the solutions became cloudy, making it opaque. Thus indicating that the precipitation of sulfur was happening.
When boiling the thiosulphate solution, there was not sign of effervescence. Thus, suggesting how the solution has a high boiling point. Strictly higher that 73°C.
Temperature (°C) ±0.5Time (s) ±0.001Rate of Reaction (s-1) (3SF)
15.0 305.750 3.27
26.0 135.310 7.39
40.0 71.560 14.0
48.0 44.190 22.6
55.0 36.980 27.0
63.0 24.830 40.3
73.0 14.970 66.8
Assuming that the same mass of sulfur has been made in each experiment, a nominal figure of 1000 units was given to calculate the rate of the reaction:
Rate of Reaction =1000timeSample calculation:
Rate of reaction for when the temperature is at 15°C
1000305.750=3.27s-1 (3SF)Percentage Uncertainty:
Percentage Uncertainty=Total UncertiantyExperimental Value×100%Percentage uncertainty when temperature is 15°C:
Percentage Error of the Thermometer=0.515.0×100%=3.33%Percentage Error of the Stopwatch=0.001305.75×100%=0.000327%Percentage Error of the 10cm3Mesuring Cylinder=0.25.0×100%=4.0%Percentage Error of the 100cm3Mesuring Cylinder=0.550.0×100%=1.00%?Total Percentage Uncertainty=1.00+4.0+0.000327+3.33?8.3%
In this graph, the general trend between the temperature and the rate of reaction is very visible. They show a directly proportional relationship, as the temperature increases the rate of reaction also increases. When the temperature is at the lowest of 15.0°C, the rate is at the slowest of 3.27s-1. On the other hand, when the temperature is at the highest of 73.0°C, the rate of reaction is the fastest of 66.8s-1.
The greatest percentage uncertainty occurs when the temperature is 15°C. Therefore the error bar for the graph will show the percentage uncertainty of 8.3% for all the rates of reactions as it will have the same random error for all of the rates of reaction.
Using this percentage uncertainty, it can be used to identify if the data points are valid. ‘Valid’ as in, the results are not formed due to random error and thus making the data point precise and accurate. As you can see, all the data points except for the one at 55.0°C, do not interfere with the range of the rates of reaction of all the other data points. However, the range at point 55.0°C tends to be intercept with the range at point 48.0°C. This, therefore, underlines the significance of random error that occurred during the experiment with 55.0°C of thiosulphate solution.
The aim for this experiment was to find the relationship between temperature and the rate of reaction. When plotting the results to the graph, it have shown significant correlation between the two and how they are directly proportional. The data that came out of this experiment can be considered to be generally precise. This can be evident by the total percentage uncertainty resulting around 8.3%. Moreover, when applied to the graph, how all the data points, except for an anomaly, were not interfering with each other’s range of error, stresses out the credibility of the results.
The reason for this directly proportional relationship is that when the thiosulphate solution gets heated up to a higher temperature, it allows the average kinetic energy of the particles to increase. Therefore, the energy provided to the particles allows for more collisions to occur as well as increasing the number of particles that have surpassed their activation energy level. Thus, increasing both the possibility for collisions with correct orientation and sufficient energy to occur. Consequently, allowing the reaction of react much faster.
Conducting the experiment, human eyes was used as a measuring instrument; to decide whether or not the cross has disappeared. However, as human eye requires a judgment of someone, there will be a lot of factors that easily can influence the decision. Subsequently, resulting in inaccurate results. Even though the same person is to record the data, there will always be an error due to their skeptical and biased judgment.
Therefore, in order to reduce this systematic error, spectrophotometer can be adopted. As this instrument measures the intensity of light relative to its wavelength, the opaqueness of the solution can be determined numerically. Hence, allowing for the results to be more accurate and precise
The distance between the person’s eyes and the cross could have been different between the experiments as no human can not stand in a solid pose after the moved to prepare for the next experiment. Thus, this varying distances could have affected the result in its inaccuracy
In order to minimize the changing of the distances, something solid and transparent (an acrylic plate for example) could be fixed a particular high, allowing the person to lean against the acrylic plate and watch the reaction from up there. As the person watches it from a fixed, limited height, the systematic error would likely reduce.
Mixing the Solutions
While adding the two reactants together, the solution was not fully fixed. How the solutions were not distributed equally, could have resulted in longer time for the reaction to occur. Thus, depending on how we have added the hydrochloric acid, the two solutions would have been mixed well or not well but never equal. Thus, some experiments taking a longer time to react and some experiments taking a shorter time.
In order to distribute the two solutions as equally as possible, using a stirring stick, the two solutions should be stirred directly after the hydrochloric is added.
During the experiment, right after the beaker was taken off the Bunsen burner, the temperature of the thiosulphate solution was continuing to rise. However, as only one temperature is recorded right after adding in the hydrochloric acid, the temperature that is reached after cannot be included within the data. The solution could be gaining heat from the beaker that has not yet been cooled down to its same temperature. Or, the solution could have lost heat, as the room temperature is a lot cooler than the heated solution. As temperature does affect the rate of reaction, it is reasonable to think that the changes of the temperature after the placement of hydrochloric acid could have had an affect in the result.
In order to solve the idea of heat lost, the experiment can be conducted in a vacuum where heat cannot be lost or gain –except contact with flame. As result, the temperature will remain constant, which will allow more accurate results.