Investigation of the rate of reaction with Sodium Thiosulphate and Hydrochloric Acid.

Repeat results and averages were taken to improve the reliability of the findings, and present solid grounding for the final conclusion. The repeat results helped to iron out any anomalies and the average gave a good summary of the results of the experiment. However if one set of results were to have been entirely different to any others, a further experiment would have been performed to replace the anomalous set of results. Fortunately, this did not happen due to cautious organisation.

Prediction:

I predict that as the concentration of Sodium Thiosulphate increases, the rate of reaction will increase. This means that the graph drawn as part of my results will have positive correlation, and will probably be curved as the increase in rate of reaction will not be exactly the same as the concentration is increased. This can be justified by relating to the collision theory. If solutions of reacting particles are made more concentrated there are more particles per unit volume. Collisions between reacting particles are therefore more likely to occur.

Results:

The time taken for the reaction to happen was recorded and can be seen on the table below.

Conc. of HCl        |    Run1        |   Run 2        |   Run3        |   Run4        |

1M                |   7.5s        |   7.15s        |   8.1s        |   7.3s        |

0.5M                |   11.5s        |   10.5s        |   11.4s        |   10.6s        |

0.25M        |   21.5s        |   21.1s        |   21.3s        |   21.3s        |

0.01M        |   69.5s        |   75.2s        |   73.5s        |   73.7s        |

0.025M        |   495.2s        |   556.7s        |   560.4s        |   537.9s        |

0.001M        |             *        |        *        |        *        |        *        |

Conc. of HCl        |   Run5        |   Run6        |   Run7        |   Run8        |

1M                |   8s                |   8.1s        |   7.4s        |   8.3s        |

0.5M                |   10.7s        |   11.2s        |   11.2s        |   11.4s        |

0.25M        |   20.8s        |   21.5s        |   21.1s        |   21.6s        |

0.01M        |   73.6s        |   71.6s        |   72.7s        |   74.3s        |

0.025M        |   535.6s        |   510.4s        |   556.1s        |   545.8s        |

0.001M        |             *        |        *        |        *        |        *        |

Conc. of HCl        | Average Time|

1M                |   7.49s

0.5M                |   11.0s

0.25M        |   21.3s

0.01M        |   72.98

0.025M        |   537.55s

0.001M        |             *

*        = These reactions ran for more than 10 minutes and did nothing in this time so we had to stop the reaction due to time restrictions.

M        = Molar

s        = Seconds

This table shows that my prediction was correct; as the concentration of Sodium Thiosulphate decreased, the time for the reaction to take place increased. Something else I noticed is that the results for the concentrations of 0.5M and 0.25M show a ratio very close to 2:1 when looking at the time for the reaction to take place. This shows that in some cases it is relevant to say that one concentration halved could result in a reaction time double that of the first concentration. This will result in a positive correlation in my results graph.

Conclusion:

We have concluded our aim of carrying out the experiment of reacting Sodium Thiosulphate and Hydrochloric Acid successfully. My prediction has been verified, and this is shown in the table of results on a previous page, as well as in the graph I have drawn. The graph shows a positive correlation with a curved line as I predicted and shows that my referral to the collision theory is also correct.

This means that, as the concentration of Sodium Thiosulphate increases, the rate of reaction does increase.

Fair Test:

In order for my findings to be valid, the experiment obviously needed to be a fair one. The reactions were carried out as fairly as we could have made them at that time. To make sure this was the case, we used the same types of beaker for the experiment so that the depth did not vary; we used the same substances in each of the reactions; we did not agitate, heat, or in any other way encourage the rate of reaction to increase; we made sure that the measuring cylinders and beakers for the Hydrochloric Acid and Sodium Thiosulphate were not mixed up – all reactions were done at room temperature.

We could have made the results more accurate by doing the experiment more times than we did, though we had already done them 8 times which should be sufficient. Another way of increasing the accuracy of the results would be to use a pipette for maximum accuracy.