Define rate of reaction - Leaving Cert Chemistry - Question 3 - 2017

One method to determine when the same mass of sulfur has been formed is to use a light sensor or a graph to monitor the cloudiness of the solution over time. The formation of sulfur will cause the solution to become increasingly opaque. We can establish a clear visual endpoint by using a colored mark underneath the reaction flask. When the mark becomes obscured, we can note the time taken for sulfur to form a consistent mass.

The concentrations filled in from the marking scheme are as follows:

• 24.0 (24 g/L)
• 18.0 (18 g/L)
• 12.0 (12 g/L)
• 6.0 (6 g/L)

The missing rates filled in from the marking scheme are:

• 0.020 s⁻¹
• 0.016 s⁻¹
• 0.012 s⁻¹
• 0.008 s⁻¹
• 0.004 s⁻¹

From the graph, we can conclude that the concentration of sodium thiosulfate is directly proportional to the rate of reaction. This demonstrates a linear relationship between concentration and rate, where an increase in concentration leads to an increase in the rate of reaction.

To repeat the process with controlled temperatures, use water baths set to a more specific temperature than 25 °C. Ensure that the reaction mixture is heated uniformly by employing a Bunsen burner or hotplate. Measure the temperature precisely before adding reactants, and maintain this temperature throughout the experiment to investigate its effect on the reaction time and rate. Record the temperature at specified intervals and create a plot of temperature versus reaction rates.