Required Practical 5

Aim

To investigate how changes in concentration affect the rates of reactions.

Materials Needed

• Dilute hydrochloric acid (HCl) solution
• Sodium thiosulfate (Na₂S₂O₃) solution
• Water
• Sodium carbonate (Na₂CO₃) tablets or calcium carbonate (CaCO₃) chips
• Stopwatch or timer
• Two identical beakers or reaction vessels
• Delivery tube
• Measuring cylinder or gas syringe
• Black marker or paper with a black cross
• Safety goggles and lab coat

Safety Precautions

• Wear safety goggles and a lab coat to protect against splashes and spills.
• Handle the chemicals carefully and follow proper disposal procedures.

Controlled Variables

• Keep the volume of the reactants constant for each trial.
• Ensure that the room temperature remains consistent throughout the experiment.

Independent Variable

• The independent variable is the concentration of the reactants (HCl and Na₂S₂O₃).

Dependent Variables

• The dependent variables are the rate of gas production and the time taken for the colour change or turbidity to occur.

Procedure - Gas Production MethodHow a writer presents perspective or viewpoint through language/structure.

1. Experimental Setup:
   1. Set up a gas syringe or delivery tube leading to a measuring cylinder filled with water.
   2. Label two identical beakers as "High Concentration" and "Low Concentration."
   3. Place the black-crossed paper behind the beakers.
2. Conducting the Experiment:
   1. Measure equal volumes of HCl solution and water (low concentration) and pour them into the corresponding beakers.
   2. Start the stopwatch and simultaneously add sodium carbonate or calcium carbonate to each beaker.
   3. Record the time taken for the gas bubble to reach the top of the gas syringe or the volume of gas produced in a set time interval (e.g., 1 minute).

Procedure - Color Change Method

1. Experimental Setup:
   1. Prepare two identical beakers, each containing the same volume of sodium thiosulfate solution.
   2. In one beaker, add a small amount of water to create a "Low Concentration" solution.
   3. In the other beaker, add less water to create a "High Concentration" solution.
2. Conducting the Experiment:
   1. Add a few drops of hydrochloric acid to each beaker containing the sodium thiosulfate solutions.
   2. Stir gently and record the time taken for the cross on the black paper to become invisible due to the colour change or turbidity.

Data Collection and Analysis

• Record the results of each trial, including the gas volume or time taken for gas production and the time taken for the colour change or turbidity.
• Repeat the experiments with different concentrations and calculate the average values.

Interpretation of Results

• Analyse the data and compare the rates of reaction for different concentrations.
• Determine if the hypothesis is supported or refuted by the experimental results.

Conclusion

• Summarise the findings of the investigation, stating how changes in concentration affect the rates of reactions.
• Discuss any trends or patterns observed in the data.
• Consider the reliability of the results and any potential sources of error.