Of thio (g/l) thio (ml) water (ml) acid (ml)
8 5 20 5
16 10 15 5
24 15 10 5
32 20 5 5
40 25 0 5
Which I will measure using burettes for thio and water and a syringe for the acid.
I will also measure the time using a stopwatch.
Range
We have chosen the following concentrations of thio for the experiment: -
8 g/l
16 g/l
24 g/l
32 g/l
40 g/l
We have chosen these because 8 g/l takes about 5 minutes, which isn’t too long, and 40 g/l which takes about 40 seconds isn’t too quick. We have chosen these results because they are evenly spaced which will be helpful when making a graph of my results.
Accuracy
I will be using burettes to measure water, thio and acid because it is 10x as accurate as measuring cylinder and I will be reading all measurements on flat surface at eye level. I also know that all readings must be taken from the bottom of the meniscus to be accurate. I aim for my results to be accurate to 5%, which means that my results must be within a certain time of each other, as is shown below: -
Concentration of thio Degree of error
8 g/l 10 seconds
16 g/l 8 seconds
24 g/l 6 seconds
32 g/l 4 seconds
40 g/l 2 seconds
Apparatus
Conical flask (50ml)- To hold reactants whilst reaction takes place.
Thermometer (0-50’c)- To measure temperature of the reactions and help keep temperature constant.
Burette (0-50ml)- To help measure accurately volumes of thio and water.
Stopwatch- Time how long it takes for cross to disappear.
Syringe (5ml)- To measure 5ml of acid accurately
Water bath- To help maintain a constant temperature for every reaction.
Paper with cross- helps measure how long reaction takes.
Step by step plan
- Collect apparatus
- Measure out thio and dilute with water if necessary (using burettes) into 50ml conical flask.
- Place thermometer into thio.
- Measure out 5ml acid using syringe.
- Take temperature of thio when it is steady and then record it.
- Place conical flask on paper with cross.
- Add acid to thio solution and start stopwatch simultaneously.
- Stop the stopwatch when cross disappears and record the time.
- Repeat experiment at least twice for each concentration.
Safety
For safety we will: -
Cover eyes with safety goggles.
Wash up all spillages of acid or thio solution immediately.
Rinse away solution immediately after reaction to minimise problems with sulphur dioxide causing asthma attacks.
Prediction
I predict the trend in my results will be as follows: -
Graph 1
Graph 2
In graph 1 I am showing an inverse relationship because as the concentration increases the time decreases. In graph 2 I am showing direct proportion because as the concentration doubles so does the rate of the reaction this is proved by the straight line. The reasoning behind this prediction is that: -
Double the concentration of thio- double the number of particles- double the number of particle collisions- double the number of successful collisions- same amount of sulphur produced in half the time.
Conclusion
The graphs in my prediction are very similar to the ones that I plotted after obtaining my results; the one showing rate against concentration of reactants shows direct proportion (graph 2) and in the one showing time against concentration of reactants shows inverse proportion (graph 1).
As I stated in my prediction as the concentration doubles so roughly does the rate, this shown by the rate for 8g/l (0.43) and 16g/l (0.97). It is also vindicated in the rate for 16g/l (0.97) and 32g/l (1.88). This agrees with my prediction because as stated there if you double the concentration of thio you double the number of particles which doubles the number of particle collisions and gives double the number of successful collisions which leads to the same amount of sulphur being produced in half the time therefore doubling the rate.
My results point to a firm conclusion because the repeats have good agreement, they are close to the line of best fit on the graph and my conclusion is in line with my prediction. I did however have one or two anomalous results but I left them out of my averaging so they don’t affect my overall results.
Evaluation
The points on my graph are quite close to the line of best fit a few are a short distance from it but this can be accounted for I believe by the temperature fluctuation in the classroom at the time of the experiments.
There is one set of results which is quite far above the line of best fit (24g/l) and I believe this can be accounted for by human error not washing the flask out properly enough or with the cross persisting in the vision of the person looking to see when the cross is no longer visible. These are the only problems I believe exist with this method.
The anomalous results that were encountered can be explained by the fact that in my results table I have recorded the temperature and the temperature of the anomalous results was significantly below those of the other readings at that concentration.
My repeat times for each concentration leaving out the 2 anomalous readings were on the whole very close together all within the 5% error margin that I stated in my plan.
The improvements that I could think of too the method are using a kind of light beam and a sensor to detect when the solution has enough sulphur in it to obscure the light (instead of looking at cross). Another thing that could be improved on would be to use a new beaker for each experiment and therefore remove the risk that the flask was not properly washed out. You could also use water baths to stop the temperature variation which causes anomalous results.
Extra work
Too expand on the investigation we could change the variable from the concentration of thio to the concentration of acid.
Mini plan
Introduction
My knowledge about the reaction between “thio” and dilute hydrochloric acid is that sodium thiosulphate reacts with the hydrochloric acid to form sodium chloride (aq) + water (l) + sulphur dioxide (g) + sulphur(s) one of the interesting things about this reaction is that it products are all the different possible states aqua, liquid, gas and solid. The symbol equation for the reaction is Na2 S2 03 + 2HCl = 2NaCl + H2o + So2 + S. What actually occurs when dilute hydrochloric acid is added to “thio” is that the solution gradually turns cloudy as a pale yellow precipitate forms, the pale yellow cloudiness is sulphur, which is not soluble in water. This knowledge I have acquired when doing an experiment into the effects of heat on the rate of reaction between “thio” and dilute hydrochloric acid.
Control of variables
The following variables will be controlled: -
Temperature- If the temperature is increased or decreased the rate of the reaction would increase or decrease with the temperature.
Amount and concentration of thio- The thio controls the amount of sulphur produced so if the amount or concentration of the thio changes so could the rate at which the sulphur is produced (and the cross disappears) so the amount and concentration of the thio must be the same for each reaction.
Total volume of reactants- acid volume must not be changed because the higher the volume the thicker the layer of solution, which could make the cross disappear quicker.
Use the same equipment- Different equipment has a different accuracy and changing the equipment e.g. conical flask may make thicker layer causing the rate at which the cross disappears to change.
Same technique and method- Use the same method for each experiment e.g. swirling because it could cause the rate of reaction to change; the same person must do each job in all the experiments to help with the reliability of results.
Measurements
Temperature- I am going to measure the temperature of the thio with a 0-50’c thermometer.
Volumes of reactants: -
Concentration volume of volume of volume
Of acid (g/l) thio (ml) water (ml) acid (ml)
8 25 20 5
16 25 15 10
24 25 10 15
32 25 5 20
40 25 0 25
Which I will measure using burettes for thio, water and acid.
I will also measure the time using a stopwatch.
Range
We have chosen the following concentrations of acid for the experiment: -
8 g/l
16 g/l
24 g/l
32 g/l
40 g/l
Accuracy
I will be using burettes to measure water, acid and thio because it is 10x as accurate as measuring cylinder and I will be reading all measurements on flat surface at eye level. I also know that all readings must be taken from the bottom of the meniscus to be accurate. I aim for my results to be accurate to 5%, which means that my results must be within a certain time of each other, as is shown below: -
Concentration of acid Degree of error
8 g/l 10 seconds
16 g/l 8 seconds
24 g/l 6 seconds
32 g/l 4 seconds
40 g/l 2 seconds
Apparatus
Conical flask (50ml)- To hold reactants whilst reaction takes place.
Thermometer (0-50’c)- To measure temperature of the reactions and help keep temperature constant.
Burette (0-50ml)- To help measure accurately volumes of acid, thio and water.
Stopwatch- Time how long it takes for cross to disappear.
Paper with cross- helps measure how long reaction takes.
Step by step plan
1.Collect apparatus
2.Measure out acid and dilute with water if necessary (using burettes) into 50ml conical flask.
3.Place thermometer into acid.
4.Measure out 25ml thio using burettes.
5.Take temperature of acid when it is steady and then record it.
6.Place conical flask on paper with cross.
7.Add thio to acid solution and start stopwatch simultaneously.
8.Stop the stopwatch when cross disappears and record the time.
Repeat experiment at least twice for each concentration.
Safety
For safety we will: -
Cover eyes with safety goggles.
Wash up all spillages of acid or thio solution immediately.
Rinse away solution immediately after reaction to minimise problems with sulphur dioxide causing asthma attacks.
Prediction
I predict the trend in my results will be as follows: -
Graph 1
Graph 2
In graph 1 I am showing an inverse relationship because as the concentration increases the time decreases. In graph 2 I am showing direct proportion because as the concentration doubles so does the rate of the reaction this is proved by the straight line. The reasoning behind this prediction is that: -
Double the concentration of acid- double the number of particles- double the number of particle collisions- double the number of successful collisions- same amount of sulphur produced in half the time.
