Ib Descomposition On Sodium Thiosulfate

IBSL06: Study of the kinetics of the descomposition of Sodium Thiosulfate.

The objective of this experiment is to determine the rate of decomposition of sodium thiosulphate (Na2S2O3) at differentconcentrations in a reaction with HCl (1,5 M). The reaction of this compound with dilute acids produces sulfur, sulfur dioxide and water. These reactions are known as ‘clock reactions’ because whenthe sulfur produced reaches a certain concentration, the solution’s color turns to a pale yellow. We will use this property to measure the rate of the reaction, as the method will consist in drawing across in a paper sheet and place the transparent solution (in a beaker) on top of it. When there is enough sulfur on it, it will be impossible to see the cross anymore, so we will measure the time ittakes, for different sodium thiosulfate concentrations, from the time the reaction starts till the moment the cross becomes invisible.
The method will consist on pouring 4 ml of 1.5 M hydrochloricacid, with a pipette, into a 25 ml solution, contained in a beaker, of a mixture of a sodium thiosulfate solution (40g/L), which was made up manually, with pipettes, and water. We will start measuringtime with a chronometer when we pour the HCl and we will stop it when the solution is opaque and unables us to see the cross in the sheet of paper.

Raw Data

Ml. of sodium thiosulfate solution (40g/L)(±0,1 ml) | Ml. of water (±0,1) | Time taken to cover the cross (seconds ± 0,005); first set | Time taken to cover the cross (seconds ± 0,005); second set |
25,0 | 0 | 12,47 | 15,00 |
20,0 |5,0 | 16,37 | 42,25 |
15,0 | 10,0 | 24,87 | 71,66 |
10,0 | 15,0 | 74,87 | 97,00 |
5,0 | 20,0 | 203,28 | 319,00 |
Table 1

It is important to say that I obtained the second set of data fromanother person so maybe our subjective view of when the cross turned invisible was different and therefore we obtained our data with slightly different parameters. Also the cross used by her was...