For a faster reaction there is a shorter time needed for the reaction to finish. The speed of the reaction is inversely proportional to the time taken for the reaction to finish.
Equipment:
- Conical flask
- Bunsen burner
- Heat proof mat
- Tripod
- Heat gauze
- Measuring cylinder
- Forceps
- Thermometer
- Timer
- Paper with a ‘X’ on it
Diagram:
Method:
I am going to investigate the rate of reaction between sodium thiosulphate and hydrochloric acid. The reactants are both colourless, but one of the products, sulphur, is yellow, so I can use this fact to follow the rates of reaction and determine the change.
First I am going to place a conical flask over a piece of paper with a cross on it. Using a dry, clean measuring cylinder I am going to measure 50cm3 of sodium thiosulphate and pour it carefully into the conical flask making sure there are no spillages as this would make it an unfair test.
I will then place the conical flask on a tripod and then will follow by heating the Bunsen burner which will then be placed under the flask to heat the sodium thiosulphate to the temperature of 82°C. I will make sure the sodium thiosulphate is 82°C with the aid of a thermometer.
Using a dry, clean measuring cylinder I will measure 5cm3 of hydrochloric acid. When the sodium thiosulphate has reached the temperature of 82°C, I will remove it from the tripod and place onto the heat proof mat. I then carefully pour the acid into the conical flask when the temperature has decreased to precisely 80°C
From the second the last drop of hydrochloric acid is poured into the conical flask I will start the timer and time how long it takes for the solution to turn cloudy and for the cross to fully disappear. I will then record this result into a table of results. I shall take readings at the following specified temperature of sodium thiosulphate; 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55 °C, 60°C. 65°C, 70°C, 75°C and 80°C.
Preliminary work:
I decided to use the specific volume of 50°C of sodium thiosulphate at this had an exact 10:1 ratio to the 5cm3 of hydrochloric acid.
Below are the results I obtained from my preliminary work.
From my preliminary work I also decided which temperatures were too high or too low for my experiment. I could see that 90°C was too high for this experiment because the solution would turn cloudy almost instantly. This would mean that results would not be very accurate because I would not be able to stop the timer in that short amount of time. I also decided to use 20°C as the lowest temperature for my experiment as the reaction was not too slow.
Variables and fair testing:
There are many aspects to consider when ensuring that the experiment is a fair test. I will have to make sure that all of the flasks and measuring cylinders are clean and dry. They have to be clean because another substance, or even the same, would alter the results and this would give an inaccurate reading. They would have to be dry because if they are slightly wet then the concentration of the solution would be changed.
Temperature is a very important factor. In this experiment a Bunsen burner is being used to control the temperature. For a fair test I am going to heat the solution two degrees above the desired temperature as this will allow time to move the conical flask onto the cross.
It is vital that the volume and concentration of the solutions and the size of the conical flask are kept the same throughout the experiment. They cannot be altered because otherwise it will lead to inaccurate results.
The only factor that I will be changing throughout the experiment is the temperature. The concentration of the solution has to stay the same. This is because in a more concentrated solution the ions are closer together, and this means that they collide more often.
Safe test:
To ensure a safe test, many factors need to be considered to avoid injury:
- Wear safety goggles
- Keep acid away from the Bunsen burner flame
- Be careful not to touch the conical flask after heating the sodium thiosulphate and to use forceps
- Be careful when handling the acid
- Keep long hair tied up
- When clearing up, make sure the tripod isn’t too hot before you touch it
- Do not drink or swallow any of the solutions
Results:
I have drawn a graph of these results showing time against temperature.
I also used these results to draw another graph to show the rate of reaction.
The rate of reaction was worked out using this equation:
Rate of reaction= 1/time
Analysis:
By looking at my graphs I can see that the prediction I made wad correct. The line of best fit I have drawn shows me that the higher the temperature, the faster he reaction took place. This is due to the fact that as the temperature increases, particles move faster which means that there will be more successful collisions. This is why the reaction was very slow at a lower temperature. I can also see this just by looking g at my table.
My results were fairly accurate. However, there are two anomalous points on my graph. These could be because of inaccurate timing or because it is sometimes difficult to see when the cross is not visible. Another reason for theses anomalous results could be because of inaccurate measuring of acid. A minor mistake could lead to the experiment being unfair as there will be a higher or lower quantity of the acid.
By looking at my table I can see that I always came very close to reaching my aim temperature. On a few occasions I did actually reach my aim temperature. The reason I only done this experiment once, without repeats, is because each time I would repeat the experiment, I would have been working at different temperatures as it is not very easy to reach the aim temperature.
Evaluation:
The anomalous results I obtained show that there is something in my experiment that can be improved. The measuring of the acid could be improved by using a burette instead of a measuring cylinder. A burette would be more precise, so I would be able to obtain more accurate results.
I tried my best throughout this experiment to make sure I obtain accurate results. I made sure the equipment I used was in good condition and I tried my best to do very accurate timing, as this was very important. Timing could have been improved. However, inaccuracy of timing was mainly due to human error.
My results could have been improved by doing repeats. If I did repeats then I would have been able to obtain an average result, and this would improve the reliability of my results.
If this experiment was repeated then I am predicting that the results would be fairly the same-when there is a higher temperature, the reaction will be faster and when there is a lower temperature the reaction will be slower. This is because of the collision theory.
To expand my investigation I could see how temperature affects the rate of reaction of a solution at a different concentration. For this experiment I would predict that as the concentration if the solution increases, the rate of reaction would also increase because the ions are much closer together in a concentrated solution which means that more successful collisions would take place.