Exam Walkthrough for AQA A-Level Chemistry
Overview
- Topic: Third required practical of AQA A-Level Chemistry
- Chemical Reaction: Between sodium thiosulfate and dilute hydrochloric acid
- Focus: Impact of temperature on the rate of reaction
Key Points
Importance of the Experiment
- Reaction involves change in turbidity, commonly performed in school labs.
- Used at GCSE level and in A-Level practical endorsements.
- Demonstrates using "one over time" as a surrogate for reaction rate.
Variables
- Independent Variable: Temperature of reagents
- Dependent Variable: One over the time taken for the reaction to complete (used as a surrogate for rate)
- Control Variables: Volumes and concentrations of solutions
Methodology
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Setting Up the Experiment
- Use water baths to heat reactants to various temperatures (do not exceed 55°C due to sulfur dioxide gas production).
- Specify volumes for consistency.
- Conduct on a micro scale to minimize sulfur dioxide gas.
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Conducting the Reaction
- Low-tech method: Use a cross on paper beneath the flask/bottle.
- High-tech method: Use a light sensor or colorimeter to detect changes in light transmission.
- Start timer when reactants are mixed.
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Measuring and Recording
- Record time until the cross disappears (low-tech) or until a predetermined absorbance/transmission level is reached (high-tech).
Repeating the Experiment
- Change the temperature while keeping volumes and concentrations constant.
- Calculate "one over time" for each temperature.
Analysis
- Plot a graph with temperature on the x-axis and "one over time" on the y-axis.
Conclusion
- Provides insights into the setup and execution of the AQA A-Level Chemistry practical.
- Encourages further experimentation and understanding of reaction rates.
Additional Notes
- Always consider safety, especially with gases like sulfur dioxide.
- Utilize technology where available to improve accuracy.
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