Quantitative Practical Skills: Concordant Results And Why They Matter (Copy)

Quantitative Practical Skills

Concordant Results And Why They Matter

Meaning of Concordant Results in ATP

• Concordant results are:
  • Titration results that are very close to each other
• In ATP:
  • Concordant results show accuracy and reliability
• Examiners treat concordant results as:
  • Proof that the technique was carried out correctly

Examiner Definition of Concordant Results

• Concordant titres are:
  • Two (or more) titre values that differ by no more than 0.10 cm³
• Any result outside this range:
  • Is not concordant
• Rough titration:
  • Is never considered concordant

Why Concordant Results Are Required in ATP

• Concordant results show:
  • The endpoint was judged consistently
  • Random errors were minimised
• Without concordant results:
  • Calculations are considered unreliable
  • Marks are lost even if calculations are correct

Core Examiner Rule

• Only concordant titres may be:
  • Averaged
  • Used in calculations
• Using a rough or non-concordant titre:
  • Automatically loses marks

Typical Titration Sequence Expected by Examiners

• Rough titration
• First accurate titration
• Second accurate titration
• Third titration if needed
• Selection of concordant values
• Calculation using the mean

Example of Titration Results Table

Identifying Concordant Results from the Table

• Compare accurate titrations only:
  • 23.60 and 23.55
• Difference:
  • 0.05 cm³
• These are:
  • Concordant
• Rough titre:
  • Ignored

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

Calculating the Mean of Concordant Results

Correct Method

• Add concordant values
• Divide by number of values used
• Round to:
  • Same decimal places as burette readings

Example Calculation

• Concordant titres:
  • 23.55 cm³
  • 23.60 cm³
• Mean:
  • (23.55 + 23.60) ÷ 2
  • = 23.575 cm³
• Rounded correctly:
  • 23.58 cm³

Common Rounding Error

• Writing:
  • 23.6 cm³
• This:
  • Loses marks

Why Rough Titrations Are Not Used

• Rough titration is:
  • Done quickly
  • Used to locate endpoint range
• Rough titres:
  • Are not precise
  • Are not reliable
• Examiner rule:
  • Never include rough titre in mean

Concordant Results and Reliability

• Reliability means:
  • Results can be repeated
  • Results are consistent
• Concordant titres:
  • Demonstrate high reliability
• Large variation:
  • Indicates poor technique

Examiner Comments from Past Reports (Pattern-Based)

• Common examiner remarks include:
  • “Candidates failed to identify concordant results”
  • “Rough titres were incorrectly used in calculations”
  • “Mean titre was calculated from non-concordant values”

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

Common Student Mistakes with Concordant Results

Mistake 1: Using the Rough Titre

• Students assume:
  • Rough result is acceptable
• Examiner response:
  • 0 marks for mean

Mistake 2: Using All Accurate Results

• Students average:
  • All accurate titres even if spread out
• Examiner expects:
  • Only values within 0.10 cm³

Mistake 3: Ignoring Decimal Precision

• Mean written to:
  • 1 decimal place
• Burette readings are:
  • 2 decimal places
• Result:
  • Mark lost

Mistake 4: Selecting Wrong Pair

• Students select:
  • Closest looking values visually
• Examiner expects:
  • Numerical comparison

Concordant Results vs Accurate Results

• ATP focuses on:
  • Concordance
  • Not theoretical accuracy

When More Than Two Concordant Results Exist

• If three titres are within 0.10 cm³:
  • Use all three
• Example:
  • 23.45, 23.50, 23.50
• Mean calculated from:
  • All concordant values

What to Do If No Concordant Results Are Obtained

• Examiner expectation:
  • Perform another titration
• Do not:
  • Guess
  • Average widely spread values

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

How Concordant Results Are Tested in ATP Questions

• Identify:
  • Concordant titres from a table
• State:
  • Which values should be used
• Calculate:
  • Mean titre
• Explain:
  • Why certain values are ignored

Examiner-Approved Explanation Phrase

• “These titres are concordant as they differ by less than 0.10 cm³”

Incorrect Explanation Phrase

• “They look close”
• “They are nearly the same”
• “They are accurate”

High-Yield ATP Checklist for Concordant Results

• Ignore rough titre
• Compare numerical differences
• Select values within 0.10 cm³
• Calculate mean correctly
• Use correct decimal places
• Use mean for all calculations

Core Scientific Principle

• Concordant results show:
  • Consistency of measurement
  • Reliability of technique
• ATP rewards:
  • Precision
  • Discipline
  • Correct selection logic
• Understanding concordant results:
  • Prevents loss of guaranteed quantitative marks