WJEC GCSE CHEMISTRY - PRACTICAL ASSESSMENT

1. Detailed Breakdown of Assessment Objectives (AOs)

• AO1: Demonstrate Knowledge and Understanding

  • Explanation: This objective assesses the student's ability to recall and comprehend scientific facts, concepts, and procedures relevant to practical tasks.

  • Example: Identifying that hydrochloric acid reacts with magnesium to produce magnesium chloride and hydrogen gas.

• AO2: Apply Knowledge and Understanding

  • Explanation: This focuses on the application of theoretical knowledge to practical scenarios, including predicting outcomes and solving problems.

  • Example: Using the reactivity series to predict that zinc can displace copper from copper sulfate solution.

• AO3: Analyze Information and Ideas

  • Explanation: This involves interpreting data, identifying patterns, drawing conclusions, and evaluating methods.

  • Example: Analyzing a graph of temperature change over time to determine the rate of an exothermic reaction.
    

2. Emphasis on Safety and Risk Assessment

• Risk Assessment:

  • Explanation: Before conducting experiments, students must identify potential hazards and implement measures to mitigate risks.

  • Example: Recognizing that acids are corrosive and wearing appropriate personal protective equipment (PPE) such as gloves and safety goggles.

• Safe Disposal of Chemicals:

  • Explanation: Proper disposal methods are essential to prevent environmental contamination and ensure safety.

  • Example: Neutralizing acidic waste solutions before disposal according to institutional guidelines.
    

3. Data Collection and Analysis

• Accurate Measurements:

  • Explanation: Precision in measuring quantities like volume, mass, and temperature is crucial for reliable results.

  • Example: Using a burette to measure 25.0 cm³ of sodium hydroxide solution accurately.

• Data Presentation:

  • Explanation: Organizing data into tables and graphs facilitates clear analysis and interpretation.

  • Example: Plotting a titration curve to determine the equivalence point in an acid-base titration.
    

4. Evaluation of Experimental Procedures

• Identifying Limitations:

  • Explanation: Recognizing factors that may affect the accuracy and reliability of results.

  • Example: Noting that heat loss to the surroundings can impact temperature measurements in exothermic reactions.

• Suggesting Improvements:

  • Explanation: Proposing modifications to enhance the validity of future experiments.

  • Example: Using a calorimeter to minimize heat loss in thermal energy experiments.
    

5. Example Practical Task: Investigating the Rate of Reaction Between Sodium Thiosulfate and Hydrochloric Acid

• Objective:

  • To study how the concentration of sodium thiosulfate affects the rate of its reaction with hydrochloric acid.

• Procedure:

  • Mix varying concentrations of sodium thiosulfate with a constant concentration of hydrochloric acid.

  • Measure the time taken for the solution to become opaque (obscuring a marked 'X' beneath the reaction vessel).

• Data Analysis:

  • Plot concentration versus time to analyze the relationship between reactant concentration and reaction rate.

• Safety Considerations:

  • Conduct the experiment in a well-ventilated area to avoid inhaling sulfur dioxide gas produced during the reaction.

6. Resources for Further Preparation

• WJEC Educational Resources:

  • Access materials offering practical hints, tips, and step-by-step guides to effectively approach practical assessments. 

• Sample Assessment Materials:

  • Review sample assessment materials to familiarize yourself with the format and expectations of practical tasks. 

• Instructions for Conducting Practical Examinations:

  • Consult the official guidelines to understand the procedures and regulations governing practical assessments.