Variables and predictions
For Investigation A, the rate of reaction on varying the concentration of H2O2, I am going to use a range of concentration, from 0.03M to 0.3M, total 10 sets of results. The 2 dependent variables, which will stay constant, are temperature and the concentration of luminol solution. I am going to use 100% luminol solution throughout this investigation; and the temperature will be room temperature, although it is varying everyday, it is still assumed constant. Since more H2O2 molecules are in 0.3M, more luminol molecules will be oxidized per second; for 0.03M H2O2, the concentration of H2O2 is 10 times smaller than that of 0.3M, which means in each seconds, there are 10 times less of luminol molecules being oxidized. I expect the time for chemiluminescence would be shorter for 0.3M and longer for 0.03M, and more light would be produced for 0.3M. The graph of the result would be either a curve or a line decreasing from low concentration to high concentration.
For Investigation B, the rate of reaction on varying the concentration of luminol, I am going to use a range of concentration, from 100% to 10%, 10 sets of results again. The 2 dependent variables, which will stay constant to obtain the fair test, are temperature and the concentration of H2O2. I am going to use 0.15M of H2O2 throughout this investigation; and same as the Investigation A, I will assume the room temperature is constant that will not affect the result too much. There are more luminol molecules in 100% solution than 10%, which means more luminol molecules can be oxidized in a second in 100% solution. I predict the time for chemiluminescence would be longer for 100% solution, and that of the 10% would be shorter, and more light would be produced for 100%, since it has more molecules to react. I also expect the graph of the result would be either a curve or a line decreasing from high concentration to low concentration.
For Investigation C, the rate of reaction on varying the temperature, I am going to use 0°C, 15°C (room temperature), 30°C, 40°C, 50°C, 60°C, 70°C and 80°C, total 8 sets of results. The 2 dependent variable, which will stay constant, are the concentration of H2O2 and concentration of luminol solution. I am going to use 100% luminol solution and 0.15M H2O2 throughout the investigation. The higher the temperature, there are more energy in the molecules. I expect the time for chemiluminescence would be shorter for higher temperature and longer for lower temperature, and the graph would be either a curve, decreasing from low temperature to high temperature, or a curve, increase to a peak then decreases gradually from low temperature to high temperature.
Investigate the rate of reaction of luminol in various factors
The reaction of the experiment can be seen easily in a darker place.
Safety
Eye protection and lab coat must be worn all the time.
Gloves have to be worn when diluting hydrogen peroxide.
Chemicals (5)
- Luminol
-
Hydrogen peroxide H2O2
-
Sodium carbonate Na2CO3
-
Sodium hydrogen carbonate NaHCO3
-
Ammonium carbonate (NH4)2CO3
-
Copper(II) sulphate CuSO4 ∙ 5H2O
Equipments required
-
250cm3 volumetric flasks
-
25cm3 pipette
- Measuring cylinder
- balance
- beaker
- timer
- water bath
- crushed ice
- test tubes
- Thermometers
Preparation
(Luminol solution)
1. Weigh out 1g Na2CO3, 6g NaHCO3, 0.15g (NH4)2CO3, 0.1g luminol,
0.1g CuSO4 ∙ 5H2O
2. Dissolve the solid in certain amount of water in a beaker.
3. Make up 250cm3 of solution with water to a meniscus.
4. Shake well before use.
(0.15M H2O2 solution)
1. Obtain 25cm3 of 5% H2O2 by a pipette.
2. Make up 250cm3 of solution with water to a meniscus.
3. Shake well before use.
(0.3M H2O2 solution)
1. Obtain 50 cm3 of 5% H2O2 by a pipette.
2. Make up 250cm3 of solution with water to a meniscus.
3. Shake well before use.
Preliminary experiments have to be done before the investigation starts. The preliminary experiments are used to give an approximation to the result. In this case, the preliminary experiment can also give samples for the end points.
Instructions
1. Add 5cm3 of luminol solution to a test tube.
2. Add 5cm3 of 0.15M H2O2 to another test tube.
3. Add the luminol solution to the H2O2, start the timer when the solution glows
4. Wait until no more light can be seen, then stop the timer.
5. Record the time taken for chemiluminescence.
6. Repeat the steps above for several times
A1. Investigation: rate of reaction in different concentration of Hydrogen peroxide (using 0.15M H2O2)
1. Put 5cm3 of H2O2 to a test tube.
2. Add 5cm3 of luminol solution to the H2O2.
3. Record the time taken for chemiluminescence.
4. Repeat the steps for several times.
5. Repeat the procedure for using 4cm3, 3cm3, 2cm3 and 1cm3 of H2O2, add water such that the test tube contains 5cm3 of H2O2 solution.
The procedure above gives the range of 0.15-0.03M of H2O2.
The table should be drawn as below:
A2. Investigation: rate of reaction in different concentration of Hydrogen peroxide (using 0.3M H2O2)
1. Put 5cm3 of H2O2 into 5 test tubes.
2. Add 5cm3 of luminol solution to the H2O2.
3. Record the time taken for chemiluminescence.
4. Repeat the steps for several times.
5. Repeat the procedure for using 4.5cm3, 4cm3, 3.5cm3 and 3cm3 of H2O2, add water such that the test tube contains 5cm3 of H2O2 solution.
The procedure above gives the range of 0.3-0.18M of H2O2.
The table should be drawn as below:
B. Investigation: rate of reaction in different concentration of luminol solution
1. Add 5cm3 of luminol solution to a test tube
2. Add 5cm3 of 0.15M H2O2 to the luminol solution.
3. Record the time taken for chemiluminescence.
4. Repeat for several times.
5. Repeat the procedure with 4.5cm3, 4cm3, 3.5cm3, 3cm3, 2.5cm3, 2cm3, 1.5cm3, 1cm3 and 0.5cm3 of luminol solution, add water to it such there is 5cm3 of luminol solution in each test tube.
The table should be drawn as below:
C. Investigation: rate of reaction in different temperature
1. Put 5cm3 of each of the 100% luminol and 0.15M H2O2 solution to 2 test tubes.
2. Put 2 test tubes into a water bath.
3. Heat the water bath to a temperature of 30°C
4. Add the luminol to the H2O2 solution
5. Record the time for chemiluminescence.
6. Repeat the steps for several times.
7. Repeat the procedure with 40°C, 50°C, 60°C, 70°C, 80°C and 0°C.
(Use Ice bath for 0°C)
Set up as follow:
The table should be drawn as below:
Storage and disposal of chemicals
Any concentration of hydrogen peroxide has to be stored in fridge, to prevent decomposition of hydrogen peroxide.
Chemicals can be disposed to the drain with large amount of water.
Equipments and chemicals
The following equipments and chemicals were used in the investigation, and the choice of equipments.
250cm3 volumetric flask
A volumetric flask is used to make up an accurate and known volume standard solution.
Pipette
A pipette is used to deliver an accurate volume of a solution, usually 25cm3. It has to be washed with distilled water and the solution once before use.
Balance
A balance is used for fast and accurate weighing. The error of 3-decimal-place balance is ±0.001g while that of 2-decimal-place balance is ±0.01g. The 3-decimal-place balance gives a more accurate weighing.
Beaker
Beaker is used to hold solution, in this case, dissolve the solid and dilute solution.
Water bath
It allows the solution rise to a certain temperature.
Crushed ice
It is used to cool down the solution to 0°C or lower.
Test tube
It is used to hold a solution.
Thermometer
It is used to measure the temperature of the water bath and ice bath.
Timer
It is used to measure the time of chemiluminescence.
Distilled Water
It is used to clean pipettes or burettes before use, to wash away the unwanted substances stick to the inner wall of the pipettes and burettes; it is also used to dilute solution, since it is not contaminated by any substance that will affect the chemical reaction.
10cm3 Measuring cylinder
It can measure different volume of solutions, to dilute to different concentration accurately.
Dropper
It can transfer small quantity of solution, e.g. 0.5cm3
Carbonates (Na2CO3, NaHCO3 and (NH4)2CO3)
The carbonates salts are used to enhance the oxidation of luminol(6).
Copper(II) sulphate CuSO4 ∙ 5H2O
It acts as a catalyst in the reaction. It also gives the luminol solution a colour of light blue.
5% hydrogen peroxide
It is an oxidant and to oxidise luminol in this reaction. If higher percentage is used, the reaction is too fast to see. Moreover, the higher the percentage, the more irritating, it may even cause burns.
Copper(II) Sulphate (CuSO4)
Harmful Harmful if swallowed. Solutions equal to or stronger than 1M should be labelled HARMFUL. It may also be irritating to the eyes and skin and has been known to sensitise the skin.
Danger to the environment It is very toxic to the aquatic environment and may cause long-term adverse effects.
If swallowed: Vomiting normally ensues. Wash out the mouth and give a glass or two of water. Seek medical attention.
If dust inhaled: Remove the victim to fresh air. If breathing is even slightly affected, seek medical attention.
If solid or solution gets
in eyes: Flood the eye with gently running tap water until a first-aider arrives.
If spilt on skin or clothes: Remove contaminated clothing. Wash off the skin with plenty of water. Soak contaminated clothing repeatedly until the rinsing water is colourless.
If spilt in laboratory: Scoop up as much as possible. Add water to the area, followed by mineral absorbent.
Disposal Add to 10 litres of water and wash it down the foul-water drain with plenty of water.
Store As a general chemical.
Sodium carbonate (Na2CO3)
Irritants Irritating to the eyes, skin and respiratory system.
Sodium bicarbonate (NaHCO3)
It has minimal hazards but would be harmful if intake in quantity.
If swallowed: Wash out the mouth and give a glass or two of water. Seek medical attention.
If dust inhaled: Remove the victim to fresh air to rest. Seek medical attention if breathing is even slightly affected.
If dust or solution gets
in eyes: Flood the eye with gently running tap water until a first-aider arrives. Unless the solution is very dilute, send the affected person to hospital and ensure that irrigation is continued during the journey.
If spilt on skin or clothes: Brush off as much solid as possible. Remove contaminated clothing. Flood the affected area with large quantities of water. If a large area is affected or blistering occurs, seek medical attention.
If spilt in laboratory: Wear eye protection and gloves. Scoop up as much as possible into a dry bucket. Add water to the area, followed by mineral absorbent.
Disposal Dissolve in 5 litres of water and wash to waste.
Hydrogen Peroxide (H2O2)
Corrosive Any solution stronger than or equal to 5.9M (i.e., 20% or 71’vol’) is corrosive and causes burns. Solutions stronger than or equal to 1.5M (i.e. 5% or 18’vol’) but weaker than 5.9M are irritants to the eyes and skin.
Dangerous with: Organic compounds such as propanone, ethanol, glycerol. Dangerous or explosive reactions can occur.
Metals and metal oxides (especially if finely divided) and Tin(II) chloride. Violent decomposition of hydrogen peroxide takes place.
Dangerous if swallowed. Causes serious internal damage due to release of oxygen.
If swallowed: Wash out the mouth and give a glass or two of water. Seek medical attention.
If solution gets in eyes: Flood the eye with gently running tap water until a first-aider arrives.
If spilt on skin or clothes: Remove contaminated clothing. Flood the affected area with large quantities of water. If a large area is affected or blistering occurs, seek medical attention.
If spilt in laboratory: Wear eye protection and gloves. Cover with mineral absorbent and clear up into a bucket. Rinse several times. Add water to dilute at least ten times before washing the liquid down the foul-water drain. The absorbent may go in the refuse.
Disposal Wear eye protection. Add slowly to 10 litres of water in a bucket and wash down the foul-water drain.
Store In a dark bottle in a cool place. Take care when removing the cap as pressure may have built up. 100’vol’ hydrogen peroxide should be kept with other corrosive liquids, non-acid and should only be diluted immediately before use (as the inhibitor, which slows down decomposition, is diluted as well). The ‘20’vol solution, purchased as such, may be stored with inorganic chemicals. Diluted solutions have a limited shelf life.
Implementing
A. Investigation: rate of reaction in different concentration of hydrogen peroxide
Anomalous Result
B. Investigation: rate of reaction in different concentration of luminol solution
Anomalous Result
C. Investigation: rate of reaction in different temperature
Anomalous Result
The data is collected in terms of time taken for chemiluminescence, which means start from the time it glows until it decays to a certain point. A preliminary experiment is done as a sample for end point and to give an approximation of time. The data is first collected by using colorimeter, to measure the rate of change of colour in a certain period. However, this will give inaccurate results, from the uncertainties of time and the colorimeter. To reduce the inaccuracy, time was measured instead. Before finding the rate equation, the data was plotted to identify the trend. Then the graphs would be modified to find the order of the reactions
A. Investigation: rate of reaction in different concentration of hydrogen peroxide
To obtain a fair test, concentration of luminol solution and temperature are stayed constant throughout this investigation.
Concentration of luminol solution: 100%
Temperature: room temperature (12-15°C)
This experiment was expected to have either a straight line decreasing from low concentration to high concentration or a curve decreasing from low concentration to high concentration. This set of data provides a curve decreasing from low concentration to high concentration, which means the smaller the molarity (concentration), the longer time of chemiluminescence, and vice versa. There is a small rise around 0.18M to 0.24M. It could be human error or equipment error. To find the order of the reaction with respect to H2O2, the graph has to be modified. The molarity (concentration) now will go to the y-axis and the time for chemiluminescence will go to the x-axis. The modified graph would be:
This graph gives a curve, but it does not have a constant half-life, which means the reaction is second order with respect to H2O2.
Rate ∝ [H2O2]2
Rate = k [H2O2]2
To verify my result, I will perform another method that uses rate-concentration graph. Tangents of each concentration are drawn, the x and y values are obtained using ratio. Since there is error for 0.18M to 0.24M, so no tangents can be drawn for that 3 concentrations. The tangents represent the rate of reaction at different concentration.
It seems the values are not adequate as some of them are large, but I just use the axis, which is easier and also gives a more accurate value. The graph of the data would be:
There is a part missing in 0.18M to 0.24M, as I mentioned before, that the 3 points are not on the curve, the tangents cannot be drawn. This graph gives a curve, which means the reaction is second order with respect to H2O2.
Moreover, if the graph of rate against (concentration)2 is plotted, and it gives a straight line, it also indicates the reaction is second order.
B. Investigation: rate of reaction in different concentration of luminol solution
To obtain a fair test, concentration of H2O2 and temperature are stayed constant throughout this investigation.
Concentration of H2O2: 0.15M
Temperature: room temperature (12-15°C)
This experiment was expected to have either a straight line decreasing from high concentration to low concentration or a curve decreasing from high concentration to low concentration. This set of data provides a straight line from high concentration to low concentration. To find the order of reaction with respect to luminol, the graph has to be modified, where concentration of luminol now goes to the y-axis and the time of chemiluminescence goes to the x-axis.
The line goes from the highest concentration to the origin (0,0). It is because there is no reaction for 0% of luminol. The straight line means the reaction is zero order with respect to luminol.
Rate = k [luminol]0
Rate = k
Retrieving rate = k, means concentration of luminol has no effect on this reaction.
C. Investigation: rate of reaction in different temperature
Anomalous result
To obtain a fair test, concentration of luminol solution and the concentration of hydrogen peroxide are stayed constant throughout this investigation.
Concentration of luminol solution: 100%
Concentration of hydrogen peroxide: 0.15M
This investigation was expected to have either an exponential curve or a curve with a peak. However, the graph was plotted as two humps (shown above). There are 2 peaks in this graph, which is 15°C and 60°C respectively. This graph first reached a peak of 15°C, then decreases to 40°C, after that, it rises to another peak of more than 70 seconds, and it decreases sharply to around 15 seconds for 80°C. There is no way I can explain the reason of the shape on the graph, it could be the human error or the equipment error, but they are less likely to happen; it could also be the characteristic of luminol. The best explanation could be the reaction of luminol does not affect by the temperature, it is because this is an oxidation, it does not necessarily require activation energy for the reaction to take place.
Now, despite of the shape of the temperature graph, to analyse the rate equation, I have:
Rate = k [luminol]0[ H2O2]2
Rate = k [H2O2]2
As a conclusion, luminol has no effect on this reaction, it is because it has zero order for the reaction, while hydrogen peroxide has second order for the reaction, which means the effect of doubling the concentration would be quadruple.
Evaluation
This method provided reliable results, but there are also some errors in it. I have done the following things to avoid as much errors as possible.
A pipette was chosen over a 50cm3 measuring cylinder to transfer solution, because it is more accurate, with ±0.06cm3 of error. A pipette has narrow diameter of inner wall, which gives a significant meniscus. It has been washed by distilled water and the solution to be delivered before use, to clean the inner wall of the pipette. A beaker is used to dissolve the solid before making up to 250cm3, to prevent any solid stick to the neck of the volumetric flask. The luminol granules are most difficult to dissolve comparing to the carbonates. When using water bath, the water bath is first fast heated to 10°C lower than the temperature to be investigated, then it is then heated to the desired temperature. This can ensure the temperature did not rise higher than the required temperature. 0.15M H2O2 was used in Investigation C, the concentration is suitable because it is not too oxidising, that the time of chemiluminescence is longer than that of 0.3M H2O2. However, I have used 0.3M and 0.15M H2O2 in Investigation A. It could be better if only 0.3M H2O2 was used, it is because it can minimise the error on using volumetric flask, although it has small relative error. The procedure has been conduct 4 times to get a more reliable result than doing once or twice each investigation. A sample has been made to determine the end point of the reaction, by comparing the colour of the product mixture. Fair tests were performed such 2 variables were remained constant when 1 variable was being investigate.
The following are the error of the equipments:
-
Weighing balance ±0.001g
-
Pipette ±0.06cm3
-
Volumetric flask ±0.15cm3
-
Timer ±0.01s
-
10cm3 measuring cylinder ±0.01cm3
Sources:
(1) Collision theory
(2)Maxwell-Boltzmann distribution
Chemical Ideas(Salters) P.223-225
(3) equation of luminol oxidation
(4) The chemiluminescence of luminol
(5) Recipe of reaction
(6) Enhancement of luminol chemiluminescence