Sodium + Hydrochloric Sodium + Sulphur + Sulphur + Water
Thiosulphate Acid Chloride Dioxide
Na2S2O3 + HCl NaCl + SO2 + S + H2O
( aq ) + ( aq ) ( aq ) + ( g ) + ( s ) + ( l )
Before I start the investigation, by having preliminary tests I can find a volume of each solution that I can use where I am able to complete the investigation in a reasonable period of time. When I am undergoing my experiment I will be making one variable. By changing the concentration of sodium thiosulphate, this is done by adding water to the solution. As I change the amount of water I put into the solution the concentration of it is changing. The more water that is put into the solution the weaker the concentration will become.
To get my preliminary results I set up the experiment as above in the diagram section, and you use different amounts of the solutions.
Use a burette to measure the amounts of the solutions needed, and put them into separate beakers. Using a funnel at the top of the burette to pout the solution into. After firstly using a measuring cylinder to measure the solution.
Use a stopwatch to time how long it takes for the cross underneath the conical flask to disappear, as the solutions are mixed together. As the reaction turns the two colourless liquids, into a milky colour afterwards.
Repeat the procedure with different amounts of the solutions, working out the best amounts that I could use for experiment.
These are the results that I received:
These preliminary testing results helped me to decide that I am to investigate the changing concentration of sodium thiosulphate as the time it takes to react, increases as the volume of it decreases.
The apparatus that I have selected to use is:
2 beakers, a conical flask, a stopwatch, a black cross, a burette, a measuring cylinder, a retort stand and clamp and a funnel.
The reason that I have chosen to use this apparatus, is that from my preliminary testing I tried different methods of measuring out the liquids, and I found that a burette gives you a much more accurate measurement than a measuring cylinder does. This is due to the fact that a burette is much slimmer and a controlled amount of liquid can be released using a tap. Whereas when using a measuring cylinder, the liquid comes out much more quickly and in a larger quantity at one time therefore making it much harder to get such an accurate measurement. Also by using 2 beakers it means that I make sure the two different liquids are put into separate beakers and not mixed by mistake.
The measurements that I am going to use in the results are seconds when timing how long the chemicals take to react, and using cm3 when measuring the chemicals.
The reason why I have chosen this range of measurements is that the time it takes to react needs to be as accurate as possible. This is why I have chosen to use this measurement, as it is more accurate than minutes, also the quickest of the reactions will take place inside of one minute. I found this out during my preliminary tests as the quickest reaction, which was the most concentrated solution, reacted in only 41 seconds.
I intend to take 5 results with a different concentration of sodium thiosulphate in each. The reason why I need to take this number of results is so that I am able to see if there is any pattern to set of results. Moreover, I will repeat the result twice so that I have more than one set of results. In case of any other results not being totally accurate due to a mistake within the investigation. Therefore, by repeating the results I can make sure of the results.
