Form Three Chemistry Practical - Effect of Concentration on Reaction Rate

Objectives: Form Three Chemistry Practical - Effect of Concentration on Reaction Rate

Form Three Chemistry Practical - Effect of Concentration on Reaction Rate

Form Three Chemistry Practical

Topic: Effect of Concentration on the Rate of Chemical Reaction

Objective: To investigate how changing the concentration of a reactant affects the rate of reaction.

Materials Required:

  • Hydrochloric acid (HCl) of varying concentrations (0.5M, 1M, 1.5M, 2M)
  • Marble chips (CaCO₃) of uniform size
  • Conical flasks (250 mL)
  • Measuring cylinder
  • Stopwatch
  • Balance
  • Gas collection apparatus (optional)

Procedure:

  1. Weigh 5 g of marble chips and place in a conical flask.
  2. Measure 50 mL of 0.5M HCl and pour into the flask, starting the stopwatch immediately.
  3. Record the time taken for the reaction to complete (or volume of gas evolved in fixed time).
  4. Repeat steps 1–3 using 1M, 1.5M, and 2M HCl.
  5. Ensure the same size of marble chips and same experimental setup for all trials.

Observations:

Record observations in a table:

Concentration (M) Time Taken (s) Rate of Reaction (1/s)
0.5 --- ---
1.0 --- ---
1.5 --- ---
2.0 --- ---

Graph: Concentration vs Rate of Reaction

Concentration of HCl (M) Rate of Reaction

Explanation:

The rate of reaction increases as the concentration of HCl increases. Higher concentration means more H⁺ ions are present, leading to more frequent collisions with the marble chips, resulting in a faster reaction.

Factors Affecting Reaction Rate:

  • Concentration: Higher concentration → faster reaction.
  • Particle size of solid: Smaller → faster reaction.
  • Temperature: Higher → faster reaction.
  • Catalysts: Can increase rate without being consumed.

Tips for Students:

  • Use same mass of marble chips for all trials.
  • Start timing immediately when adding acid.
  • Repeat the experiment for accurate results.
  • Label graph axes clearly with units.

Common Mistakes:

  • Using different amounts of marble chips.
  • Starting stopwatch late.
  • Mixing up acid concentrations.
  • Not cleaning apparatus between trials.

Example Video Demonstration

Form Three Chemistry Practical

Topic: Effect of Concentration on Reaction Rate using Sodium Thiosulphate

Objective: To investigate how changing the concentration of sodium thiosulphate (Na₂S₂O₃) affects the rate of reaction with hydrochloric acid (HCl).

Materials Required:

  • Sodium thiosulphate solution (various concentrations: 0.1M, 0.2M, 0.3M, 0.4M)
  • Hydrochloric acid (1M)
  • Conical flasks (100 mL)
  • Measuring cylinders
  • Stopwatch
  • White paper with black cross marked on it
  • Beakers, pipettes, funnel

Procedure:

  1. Place a white paper with a black cross under a 100 mL conical flask.
  2. Measure 50 mL of 0.1M sodium thiosulphate and pour into the flask.
  3. Add 5 mL of 1M HCl to the sodium thiosulphate and start the stopwatch immediately.
  4. Observe the black cross through the solution; stop timing when the cross disappears (solution becomes opaque).
  5. Record the time taken for the cross to disappear.
  6. Repeat steps 2–5 using sodium thiosulphate concentrations 0.2M, 0.3M, and 0.4M.

Observations:

Concentration of Na₂S₂O₃ (M) Time Taken (s) Rate of Reaction (1/s)
0.1 --- ---
0.2 --- ---
0.3 --- ---
0.4 --- ---

Graph: Concentration vs Rate of Reaction

Concentration of Na₂S₂O₃ (M) Rate of Reaction

Explanation:

The reaction of Na₂S₂O₃ with HCl produces sulfur, which makes the solution opaque. Higher concentration of Na₂S₂O₃ increases the number of particles per unit volume, leading to more frequent collisions with H⁺ ions and faster reaction.

Factors Affecting Rate:

  • Concentration: Higher concentration → faster reaction.
  • Temperature: Higher temperature → faster reaction.
  • Surface area (if solid reactant used): Smaller particles → faster reaction.
  • Catalysts: Speed up reaction without being consumed.

Tips for Students:

  • Ensure same volume of acid and solution for each trial.
  • Start stopwatch immediately when acid is added.
  • Repeat trials for accuracy and calculate mean time.
  • Use clean apparatus to avoid contamination.

Common Mistakes:

  • Not using same volume of solution for each trial.
  • Starting stopwatch late.
  • Not observing the exact moment cross disappears.
  • Mixing up concentrations.

Sample Questions & Solutions:

  1. Question: The time taken for 0.2M Na₂S₂O₃ to react with HCl is 50 s. Calculate the rate of reaction.
    Solution:
    Rate = 1 / time = 1 / 50 s = 0.02 s⁻¹
  2. Question: Draw a graph of concentration (x-axis) vs rate of reaction (y-axis) using data: 0.1M → 0.01 s⁻¹, 0.2M → 0.02 s⁻¹, 0.3M → 0.03 s⁻¹, 0.4M → 0.045 s⁻¹.
    Solution: Use the SVG graph above as example. Plot points and join smoothly; rate increases with concentration.
  3. Question: Explain why the reaction rate increases with concentration.
    Answer: Higher concentration → more particles per unit volume → more frequent collisions → higher reaction rate.

Conclusion:

The experiment shows that increasing the concentration of sodium thiosulphate increases the reaction rate, consistent with collision theory. Accurate timing and repeated trials ensure reliable results.

Conclusion:

The experiment confirms that increasing the concentration of a reactant increases the rate of reaction. This demonstrates the collision theory, where more particles per unit volume lead to more frequent successful collisions.

Reference Book: N/A

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