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The effect of temperature on the rate of the reaction between a sodium thiosulfate solution and a hydrochloric acid solution was investigated - Leaving Cert Chemistry - Question 3 - 2020
Question 3
The effect of temperature on the rate of the reaction between a sodium thiosulfate solution and a hydrochloric acid solution was investigated. In each run, a stopwat... show full transcript
Worked Solution & Example Answer:The effect of temperature on the rate of the reaction between a sodium thiosulfate solution and a hydrochloric acid solution was investigated - Leaving Cert Chemistry - Question 3 - 2020
Step 1
With the aid of a labelled diagram describe a method for adjusting and measuring the temperature of the reaction mixture for the runs above.
Answer
To adjust and measure the temperature of the reaction mixture, the following steps should be taken:
- Setup the Apparatus: Use a water bath heated by a Bunsen burner to control the temperature of the sodium thiosulfate solution. Place the flask containing the solution in the water bath.
- Insert a Thermometer: Insert a thermometer into the water bath to monitor the temperature accurately.
- Mix Solutions: Thoroughly mix the sodium thiosulfate solution with hydrochloric acid just before starting the reaction. Add the acid to the flask and swirl gently.
- Record the Temperature: Observe and record the temperature of the mixture immediately after mixing.
- Measure Temperature Consistency: Ensure that the reaction mixture reaches a stable temperature before starting the timing for the reaction.
By following these steps, precise control of the temperature can be achieved, which is crucial for observing the effects on reaction rates.
Step 2
What was observed in the reaction flasks during each run?
Answer
During each run, as the temperature increased, a noticeable change occurred in the reaction process:
- At lower temperatures (e.g., 20 °C), the reaction results in slower formation of a precipitate, making it more challenging to observe the reaction's endpoint.
- As the temperature rose (e.g., 40 °C and above), the formation of the precipitate became faster and more pronounced, indicating a quicker reaction time. This observation illustrates the relationship between temperature and reaction rate.
Step 3
Describe how this observation was used to obtain the reaction times.
Answer
The observation regarding the rate of formation of the precipitate was used to time the reactions:
- Each flask was monitored until the precipitate obscured a marked cross beneath it (or until obscured by a smartphone light meter).
- The time taken from the addition of hydrochloric acid until the cross was no longer visible was recorded. This time measurement was used as a quantitative indicator of the reaction time, which could then be analyzed against the various temperatures for further study.
Step 4
Step 5
Plot a graph of initial reaction rate (r) versus temperature (T).
Answer
To plot the graph:
- Label the axes: The X-axis should represent the Temperature (°C) and the Y-axis should represent the Initial Reaction Rate (r, s⁻¹).
- Plot the Data Points: Based on the table values, accurately plot the points for each run.
- Draw the Curve: Connect the data points smoothly to show the relationship between temperature and the reaction rate. Ensure no breaks or jagged lines are present.
Step 6
Use your graph to find an approximate value for x in the following statement: The rate of this reaction doubles for every x °C rise in temperature.
Answer
Using the graph, analyze the slope of the curve. Check points where the reaction rate approximately doubles:
- For example, if the rate at 20 °C is 0.002 and the rate at 40 °C is about 0.029, estimate the x-value. The calculation shows that a 20 °C increase corresponds to a doubling of rate approximately. Thus, x can be approximated as 20 °C.
Step 7
Explain this result.
Answer
This result can be explained by the collision theory of chemical reactions:
- Increased Temperature: As the temperature rises, particles gain kinetic energy, leading to more frequent and energetic collisions between reactant particles.
- Successful Collisions: With more collisions occurring, a higher number of successful reactions happen per unit time, effectively doubling the rate for every increase of approximately x °C.
- Endothermic Nature: This observation demonstrates a fundamentally endothermic reaction that accelerates with heat.
Step 8
Is the depth of liquid in the flask in this Run 8 greater or less than in the original flasks? Justify your answer.
Answer
The depth of liquid in the flask for Run 8 is greater than in the original flasks. This is supported by the observation that the new flask shape is deeper while the same volume of solution is used:
- Volume Consistency: Each run (including Run 8) used 100 cm³ of Na2S2O3 solution, ensuring that volume remains constant.
- Flask Shape Impact: A deeper flask results in a greater liquid depth, despite using the same volume. Consequently, the reciprocal of the reaction time will be influenced by this greater depth.