Sodium Thiosulphate + Hydrochloric acid → Sodium Chloride + Sulphur + Sulphur dioxide + Water
Na2S2O3 (aq) + 2HCl (aq) → 2NaCl (aq) + S (s) + SO2 (g) + H2O (l)
Ionic Equation:
S2O3 (aq) + 2H (aq) → H2O (l) + S (s) + SO2 (g)
Results
Conclusion
From our Volume/Time graph we can tell that the more concentrated the Sodium Thiosulphate is, the quicker the reaction takes. From our 1÷time/volume graph we got a straight line graph through points 0,0. This means that the concentration of Sodium Thiosulphate and 1/time are directly proportional to each other. This means that when the concentration of Sodium Thiosulphate doubles, the reaction takes place twice as fast. This is because when the concentration doubles, the amount of Sodium Thiosulphate particles doubles, so collisions of Sodium Thiosulphate and Hydrochloric acid ions occurs twice as often. This means that the reaction is complete twice as quick, and the liquid will cloud up so we can’t see the cross in half the time. For example when the volume of Sodium Thiosulphate was 20cm³ and volume of water was 30cm³, the result for 1/time was 0.009s . And when the volume of Sodium Thiosulphate was 40cm³ and volume of water 10cm³, the 1/time result was 0.018s . This is double the speed of half the concentration.
Particle diagram:
This shows that twice the amount of Sodium Thiosulphate particles there are the twice as likely they are to hit and react with a Hydrochloric acid ion to complete the reaction and make the cross disappear from site.
Sodium Thiosulphate + Hydrochloric acid → Sodium Chloride + Sulphur + Sulphur dioxide + Water
Na2S2O3 (aq) + 2HCl (aq) → 2NaCl (aq) + S (s) + SO2 (g) + H2O (l)
Ionic Equation:
S2O3 (aq) + 2H (aq) → H2O (l) + S (s) + SO2 (g)
Within experimental error I got a straight line graph through points 0,0. this means that the concentration of Sodium Thiosulphate is directly proportional to the time in which the cross takes to disappear. The conclusion supports my prediction as I said that twice the concentration would double the speed of the reaction and that this was because there were twice as many Sodium Thiosulphate particles to collide and react with the Hydrochloric acid ions. This is what did happen so my prediction is correct.
Evaluation
In this investigation we had a few experimental errors. This would have been from not having exactly the right amount of each solution which would have creates false results. Or we could have not been very accurate with the timing or we did not get exactly the same position on each time that the cross had completely disappeared from sight. This could have easily been wrong as sometimes we may have stopped timing before or after the cross had completely disappeared. We may have been at different angles looking down on the cross through the solution which would mean that the cross may seem to disappear from one angle but may be still seen from another angle.
To improve the reliability of the experiment we could put a light under the conical flask, instead of a cross. And use a light sensor attached to a computer program which would stop timing when the light had disappeared. The light would have to be quite dim otherwise it may shine through the liquid even when it had clouded up. It would also have to be done in the dark so that there is no interference from other light sources. We could improved the reliability of the experiment by using more accurate measuring equipment, such as a syringe to measure the liquids.
We could extend our work further by using other acids besides Hydrochloric acid and note if there is any difference in time, if any. We could add a catalyst and vary the amount or size of the catalyst bits and not change the amounts of each solution. We could vary the temperature of the experiment by heating or cooling the Sodium Thiosulphate mixture and note the time for the same concentration.
