In the reaction between sodium thiosulphate solution
and dilute hydrochloric acid, increasing the concentration of sodium thiosulphate
means that there will be less time before the cross can no longer be seen
(the sulphur will be produced more quickly). Therefore if you dilute the sodium thiosulphate, more time is taken as it will take longer for the cross to disappear.
HCl + sodium thiosulphate ± sodium chloride + sulphur dioxide + sulphur + water
HCl(aq) + Na2S2O3(aq) ± NaCl(aq) + SO2(g) + S(s) + H2O(l)
When making different concentrations of sodium thiosulphate, you should take care to use the same total volume (of sodium thiosulphate plus hydrochloric acid) for the comparison to be correct.
The effect of concentration:
The more concentrated the solutions, the more quickly they react. When you increase the concentration you are increasing the number of particles in that volume of solution, this will speed up the reaction, as the more particles there are the more collisions are happening increasing the reaction.
Prediction:
I predict that increasing the concentration it will make the particles collide and a reaction will happen quicker. What I think would happen is that the bonds will break and more bonds will be made therefore increasing the reaction.
Method:
- I will make a copy of a table, to put my results in.
- I will then measure out 50cm3 of sodium thiosulphate and put into a measuring cylinder, I will then pour it into a conical flask, I will keep this measuring cylinder for sodium thiosulphate only, otherwise if it mixed with the hydrochloric acid it would effect my results and not make it a fair test.
- On a piece of paper/card I will draw a THICK black cross, then I will stand the conical flask over the cross.
- I will then measure 5cm3 of bench hydrochloric acid in a measuring cylinder; this cylinder will be only used for hydrochloric acid.
- I will then pour the acid into the sodium thiosulphate solution, at the same time my partner will start the stopwatch. I will swirl for 2 seconds, then place it back down and then swirl for another 2 seconds. I will do that to every test, if I change it then it will be an unfair test. At the same time my partner will start the stopwatch
- I will watch the cross and time how long it takes for the deposit of sulphur to hide the cross from sight; I will enter the time taken into the table I have already prepared.
- I will then wash out the conical flask and repeat the experiment, keeping EVERYTHING the same apart from the concentration!
Fair Testing:
- I will keep all measurements the same.
- I will keep the same temperature.
- The same equipment will be used.
- The observer will be the same, as the eyesight of one person may be different to another.
- The background will stay the same, and the place will stay the same as well, because the light might be different in a different place and this will affect the results, the weather can also affect the results.
- The cross will stay the same colour and thickness; I will always go over it before every test as it might begin to wear off with the water, acid and sodium thiosulphate.
Pre-test 1:
Conclusion of my pre-test
My results show me that there is a pattern happening; it’s not an obvious pattern but you can clearly see that the time is going up as I dilute the sodium thiosulphate.
