Titration calculations (as required)

Titration is a quantitative technique used to determine the concentration of an unknown solution by reacting it with a solution of known concentration. The solution of known concentration is called the standard solution, while the solution being analyzed is the analyte.

Key Terms:

• Titre: The volume of solution added from the burette during a titration
• End point: The point at which the indicator changes color, signaling that the reaction is complete
• Concordant results: Titres that agree within 0.10 cm³ of each other
• Mean titre: The average of concordant titres only

Essential Equipment:

• Burette: Measures variable volumes accurately to ±0.05 cm³
• Pipette: Measures fixed volumes (e.g., 25.0 cm³) accurately
• Conical flask: Contains the analyte solution
• Indicator: Shows the end point (phenolphthalein or methyl orange)

The Titration Formula:

Mole relationship: n = c × V (where n = moles, c = concentration in mol/dm³, V = volume in dm³)

Conversion: Volume in cm³ ÷ 1000 = Volume in dm³

Calculation Steps:

1. Write the balanced equation
2. Calculate moles of known substance using n = c × V
3. Use mole ratio from equation to find moles of unknown
4. Calculate concentration: c = n ÷ V

Mnemonic: BURP

• Balanced equation first
• Use n = cV for known
• Ratio from equation
• Product calculation (unknown concentration)

Why Titrations Matter:

Titrations are used extensively in real-world applications. Water treatment plants use titrations to monitor acidity levels in drinking water. Pharmaceutical companies verify medication concentrations to ensure patient safety. Winemakers test acidity in wine to maintain quality. Even swimming pool maintenance relies on titrations to check chlorine and pH levels.

The Coffee Shop Analogy:

Think of titration like making the perfect cup of coffee. You know exactly how much coffee grounds you need (your standard solution), but you're testing different water amounts (the analyte) to find the ideal strength. The "end point" is when you taste it and say "perfect!" The indicator is like your taste buds – it tells you when you've reached the right balance.

Understanding the Process:

During an acid-base titration, imagine hydrogen ions (H⁺) from the acid seeking out hydroxide ions (OH⁻) from the base. They combine to form water in a neutralization reaction. The indicator molecule is sensitive to pH changes – it exists in two different colored forms. At the end point, the last drop of titrant causes a sudden pH change, triggering the indicator to switch color dramatically.

Real Laboratory Application:

A quality control chemist at a vinegar factory needs to verify that bottles contain 5% acetic acid (ethanoic acid). By titrating a measured sample against standardized sodium hydroxide, they can calculate the exact concentration. If it's too low, customers complain about weak flavor; too high, and it becomes unsafe for consumption. This single titration protects both product quality and consumer safety.

Example 1: Classic Acid-Base Titration

Question: 25.0 cm³ of sulfuric acid (H₂SO₄) required 23.50 cm³ of 0.100 mol/dm³ sodium hydroxide (NaOH) for complete neutralization. Calculate the concentration of the sulfuric acid.

Step 1: Write balanced equation H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O

Step 2: Calculate moles of NaOH (the known)

• Volume in dm³ = 23.50 ÷ 1000 = 0.02350 dm³
• Moles = c × V = 0.100 × 0.02350 = 0.002350 mol

Step 3: Use mole ratio (1:2)

• Moles of H₂SO₄ = 0.002350 ÷ 2 = 0.001175 mol

Step 4: Calculate concentration

• Volume H₂SO₄ = 25.0 ÷ 1000 = 0.0250 dm³
• Concentration = n ÷ V = 0.001175 ÷ 0.0250 = 0.0470 mol/dm³

Examiner note: Always show the mole ratio clearly – this is worth at least 1 mark

Example 2: Mean Titre Calculation

Results: Rough = 24.80 cm³, Titre 1 = 24.15 cm³, Titre 2 = 24.20 cm³, Titre 3 = 24.10 cm³

Solution:

• Identify concordant: 24.15, 24.20, 24.10 (all within 0.10 cm³)
• Mean = (24.15 + 24.20 + 24.10) ÷ 3 = 24.15 cm³
• Never include rough titre in the mean

Examiner note: State which values you're using – examiners award marks for working