Rates, Energy & Reaction Experiments: Rate Of Reaction Experiments (Gas Collection, Mass Loss) (Copy)

Rates, Energy & Reaction Experiments

Rate Of Reaction Experiments (Gas Collection, Mass Loss)

Purpose of Rate of Reaction Experiments in ATP

• Used to measure how fast a chemical reaction occurs
• ATP questions assess:
  • Correct experimental setup
  • Accurate measurement techniques
  • Ability to calculate rate
  • Interpretation of trends and results
• Examiners reward:
  • Methodical, stepwise approach
  • Proper apparatus
  • Correct units

Core Examiner Rule

• Rate = Amount of reactant used ÷ Time or Amount of product formed ÷ Time
• Must include:
  • Accurate initial readings
  • Consistent time intervals
  • Proper units (cm³/s or g/s)
• Stepwise description required for gas collection and mass loss methods

1. Gas Collection Method

Purpose

• Measures volume of gas produced as reaction progresses

Apparatus

• Conical flask
• Delivery tube
• Gas syringe or inverted measuring cylinder over water
• Stopwatch

Method

1. Mix reactants in conical flask
2. Connect flask to gas collection apparatus
3. Start stopwatch immediately
4. Record volume of gas at regular intervals
5. Continue until reaction completes or slows significantly

Observations

• Volume of gas (cm³) at specific time intervals (s)
• Plot graph: Volume of gas (y-axis) vs Time (x-axis)

Rate Calculation

• Rate = ΔVolume ÷ ΔTime
• Example: 24 cm³ gas collected in 60 s → Rate = 24 ÷ 60 = 0.40 cm³/s

Examiner Notes

• Stop stopwatch immediately when reaction starts
• Ensure gas syringe not overfilled
• Avoid leaks in tubing
• Use concordant repeats if required

Written and Compiled By Sir Hunain Zia, World Record Holder With 154 Total A Grades, 7 Distinctions and 11 World Records For Educate A Change O Level And IGCSE Chemistry Full Scale Course

2. Mass Loss Method

Purpose

• Measures decrease in mass of reaction mixture as reaction produces gas

Apparatus

• Conical flask
• Cotton wool stopper
• Balance (sensitive to 0.01 g)
• Stopwatch

Method

1. Place reactants in conical flask
2. Cover with cotton wool to allow gas escape
3. Place flask on balance, zero it
4. Start stopwatch immediately
5. Record mass at regular intervals
6. Continue until mass stabilises

Observations

• Mass of flask decreases over time
• Plot graph: Mass loss (g) vs Time (s)

Rate Calculation

• Rate = ΔMass ÷ ΔTime
• Example: 0.30 g mass lost in 50 s → Rate = 0.30 ÷ 50 = 0.006 g/s

Examiner Notes

• Cotton wool prevents spillage but allows gas escape
• Balance must be on stable surface
• Record readings quickly and accurately
• Ensure repeatable measurements

Comparison of Gas Collection vs Mass Loss

Step 3: Plotting and Interpreting Data

• Graphs typically:
  • Gas volume / mass lost (y-axis) vs Time (x-axis)
  • Steeper initial slope = faster reaction
  • Flattening curve → reaction slowing down
• Examiner expects:
  • Correct axes and units
  • Proper best-fit line or smooth curve

Step 4: Common Examiner Traps

• Using wrong units for rate
• Starting stopwatch late
• Leaks in gas apparatus
• Not using concordant repeats
• Recording mass with stopper sealed → inaccurate

High-Yield ATP Tips

1. Identify correct method based on product measurement (gas vs mass)
2. Use appropriate apparatus carefully
3. Record readings at regular intervals
4. Calculate rate = ΔQuantity ÷ ΔTime
5. Plot graph with correct axes, units, and scale
6. Use best-fit line or smooth curve for trend interpretation

Core Scientific Principle

• Rate of reaction depends on:
  • Concentration, temperature, surface area, catalysts
• Accurate measurement of gas produced or mass lost:
  • Allows quantitative determination of rate
• Mastery of experimental technique and calculation:
  • Secures high ATP marks in kinetics experiments

Written and Compiled By Sir Hunain Zia, World Record Holder With 154 Total A Grades, 7 Distinctions and 11 World Records For Educate A Change O Level And IGCSE Chemistry Full Scale Course