Form Three Chemistry Practical

Topic: Effect of Particle Size on the Rate of Chemical Reaction

Objective: To investigate how the particle size of a solid affects the rate of reaction with a solution.

Materials Required:

• Hydrochloric acid (HCl) 1M
• Marble chips (CaCO₃) of different sizes (large, medium, small)
• Conical flasks (250 mL)
• Measuring cylinder
• Stopwatch
• Balance
• Delivery tube and gas collection setup (optional)

Procedure:

1. Measure 50 mL of 1M HCl using a measuring cylinder and pour into a 250 mL conical flask.
2. Weigh 5 g of large marble chips and add to the acid. Start the stopwatch immediately.
3. Observe and record the time taken for the reaction to complete (or volume of gas evolved in fixed time).
4. Repeat steps 1-3 using medium-sized marble chips and then fine powdered marble chips.
5. Compare the rates of reaction for different particle sizes.

Observations:

Record your observations in a table like this:

Explanation:

The rate of reaction increases as the particle size decreases. This is because smaller particles have a larger surface area exposed to the reactant, allowing more frequent collisions between reactant particles, thus increasing the reaction rate.

Factors Affecting Reaction Rate:

• Particle size: Smaller particles → higher rate.
• Concentration of reactants: Higher concentration → higher rate.
• Temperature: Higher temperature → faster reaction.
• Catalysts: Presence can increase rate without being consumed.

Conclusion:

The experiment clearly shows that smaller particle size increases the rate of reaction due to larger surface area, which allows more collisions per unit time. This is consistent with collision theory.

Other Examples of Reactions Showing Effect of Particle Size:

• Calcium Carbonate with Hydrochloric Acid (CaCO₃ + HCl → CaCl₂ + CO₂ + H₂O)
  Observation: Fine powdered CaCO₃ reacts faster than large marble chips because it has more surface area exposed to HCl.
  Explanation: Smaller particles → higher surface area → more frequent collisions → faster reaction.
• Zinc with Hydrochloric Acid (Zn + 2HCl → ZnCl₂ + H₂)
  Observation: Finely powdered zinc reacts faster than zinc granules.
  Explanation: Powdered zinc exposes more surface area to acid → more collisions → faster hydrogen gas evolution.
• Magnesium with Hydrochloric Acid (Mg + 2HCl → MgCl₂ + H₂)
  Observation: Thin magnesium ribbons react faster than thick ribbons.
  Explanation: Thinner ribbons have more surface area relative to mass → faster reaction rate.
• Iron with Sulfuric Acid (Fe + H₂SO₄ → FeSO₄ + H₂)
  Observation: Finely divided iron filings react faster than chunks of iron.
  Explanation: More surface area → more collisions → faster gas evolution.