Investigating the effect of changing temperature on the rate of reaction between sodium thiosulphate (Na2S2O3) and hydrochloric acid (HCL).

Preliminary Work

Work that I’ve done before this investigation is the same experiment as this but changing the concentration of the sodium thiosulphate by adding more water but keeping it at the same temperature. It was from this I chose the concentration of the sodium thiosulphate for this experiment. I chose 40cm³ of the thiosulphate and 10cm³ of water to dilute it with. I chose these measurements because the reaction was quicker then using a more dilute mixture. This is because, as the concentration increases, the particles are closer together so the collision frequency increases and there are more particles reacting per second.

Results –

Conclusion –

My graph shows that as the temperature increases, the rate of reaction increases. Also, as the temperatures get higher the rate increases more and more. You can tell this from the line of best fit on the graph getting steeper as the temperature goes up. The reason this happens is the same as I predicted. It’s because if you increase the temperature, the particles move faster. As they are moving faster, there are more collisions in a certain time and are more vigorous to react. This makes the rate of reaction increase as more heat energy is exposed to it.

Method Evaluation –

In getting prepared for the investigation was easy but it was hard to get every measurement so exact. I think my investigation was a success in that I got the results I expected. To be more exact I could have been more efficient on stopping the stopwatch at the exact time the cross disappeared. The chemicals could have been measured out more clearly by using more accurate equipment, such as a smaller measuring cylinder with more points on. Another problem I thought at the start was the change in mass of the sodium thiosulphate and water mixture whilst heating. Some of the mixture could have been evaporated making it an unfair test because as you heat it more, more mixture gets the chance to be evaporated. But the change in mass would be so small it wouldn’t be worth worrying about. Even though I repeated my first measurement, I still didn’t think the results were much the same so I had to repeat it for a third time and it appeared in the middle of the two I had already done. To make my results fully reliable I could have repeated all the results. Any further work I could have done to provide additional evidence could have been testing a wider range of temperatures, testing temperatures in-between the original temperatures so there are more points on the graph for a more accurate line of best fit. Also using more accurate apparatus could have made my results more reliable. Such as a digital thermometer that gives you an exact temperature.

Results Evaluation –

All my results show a clear pattern. The temperature increases as the rate of reaction increases. All my points are quite close to the line of best fit. All my points are good enough to male me feel confident bout the line of best fit and support my conclusion well. As the rates increased, the reliability of my results declined. This is because on the graph I made the line of best fit gets steeper and as the rates get faster a small mistake could make a big difference in the result. These may course any anomalies. The only bad results I had was on the first temperature (40°c) where I had to repeat it two more times because the first repeat had a big difference to the original. This was just a human error on my part as I wasn’t paying my full attention when I first got started.