Method
I am aware that there are many safety precautions which I will have to follow:
- Immediately wash hands and other parts of skin if incontact with hydrochloric acid as it is an irritant and is harmful to skin and eyes.
- Rinse out mixture in flask and leave water running to get rid of the chemicals including sulphur dioxide gas which is released in the reaction and is toxic.
- Wear safety glasses to protect your eyes
- Keep hair tied back and clear any bags which are in the way
- Clean up any spills which could occur during the expeiment.
This is the method which i will use to perform my experiment:
- Clear surface area and set up aparatus
- Set up three measuring cylinders, one measuing cylinder for each solution, sodium thiosulphate, hydrochloric acid and water to the appropriate measurements. For each experiment keep the volume of sodium thiosulphate at 40cm³. I will begin the experiment with the volume of hydrochloric acid at 40cm³ and the volume of water at 0cm³. The measurements will then be as follows:
I have chosen these measurements as I think they will give me a good range of results. I think that 40cm³ is a good volume to keep the mixture at as its big enough to show a visible result in the flask and does not use to much chemical wasting it.
- Pour the correctly measured hydrochloric acid, sodium thiosulphate and water into a flask where the chemicals will react.
- As soon as the mixture is in the flask, start the stopwatch and watch the mixture react, turning cloudy and time how long the reaction takes to become completely cloudy.
- Stop the stopwatch when the mixture has become too cloudy for the cross to be visible.
- Record the time in a results table and repeat each experiment, three times to then find the average time of each reaction.
- Wash the flask before proceeding with next reaction
- Do this for each concentration of hydrochloric acid
I will ensure my experiment will be fair by keeping the sodium thiosulphate consistant throughout the experiment, it is my solution which I am keeping constant at 40cm³.I will make sure I measure the hydrochloric acid and water accurately using the correct measuring cylinders for each chemical. I will ensure I stop the reaction at the same point of visibility for each time. I will wash out the flask after every use to get rid of any left over chemicals from the previous reaction.
Other factors which effect the rate of reaction and could alter my results are:
- the presence of light
- the temperature
- the size of the particles of a solid reactant
I will control these factors by keeping them all constant throughout the experiment, the temperature will stay at room temperature.
I have decided to run a pre-trial test to check if my method is practical to use for my experiment. I will use three readings for my pre-trial, there will be one reading from using a stong concentration of hydrochloric acid, one using a weak concentration and one with a middle concentration. My results will show me if my chosen sizes and volumes are suitable to achieve a good range of results.
These are the results from my pre-trial test showing the rate of reaction using a strong and weak concentration of hydrochloric acid.
There are no faults in my results and they show a good range between the strongest and weakest concentrations.I am happy with these results so I am going to keep my method the same for my experiment.
Results
This is a table of my results which I got from my experiment:
Conclusion
From my results, I have found that as the concentration of hydrochloric acid, the rate of reaction became faster. This proves my prediction to be correct. The time taken for the 'X' to be hidden decreases as the concentration of hydrochloric acid increases. This also proves my prediction to be correct. The faster the reaction took place, the shorter the time needed for the reaction to finish. This means the speed of the reaction is inversely proportional to the time taken for the reaction to finish. The rate of reaction is proportional to the concentration of hydrochloric acid. This is shown on the graph, the speed doubles when the concentration is doubled. The reason for this is that the ions are closer together in a concentrated solution. The closer together they are, the more often the ions collide. The more often the collide, the more chance they have of reacting.
Evalutaion
From my experiment I have obtained an accurate set of results which show me a precise pattern from which I expected. From my graph all of my points are near to the line of best fit which shows the quality of my results are good and I have no sign of anomolous results, they all fit the same pattern.Throughout my investigation I follwed my method which was successful, I managed to conduct my experiment thouroughly and collect good, accurate result. I did not come across any difficulties whilst performing my investigation, the experiment was fair meaning my results are valid.
The equipment we were given to use for the experiment was quite basic, but the outcome was still good and gave me my expected results.To improve this experiment I could have used more sophisticated equipment to measure the solutions. I was given measuring beakers which were quite inaccurate, I would have much rather of used a burette. As the measuring beaker was not accurate, it means that the measurement of the solutions were not accurate. This could have lead to my results not being flawless either. If I were to perform this experiment again, I would improve it by using a more accurate way of observing the 'X' disappearing, perhaps by using an opto-electronic system to measure when the solution becomes opaque. This would eliminate human error.