Analytical and Applied Chemistry
Analytical and Applied Chemistry
This domain connects laboratory measurement with real materials: volumetric and gravimetric analysis, instrumental methods, polymers, dyes, drugs, fertilisers, soaps and detergents. NEB questions often use a short calculation followed by an applied-reasoning part.
Core rules
- In titration, moles relate through the balanced equation, not directly through volumes. For NaOH + HCl, n-factor is 1 for both; for H2SO4 + NaOH, one mole of acid neutralises two moles of base.
- Indicators must change near the equivalence pH: phenolphthalein for weak acid–strong base, methyl orange for strong acid–weak base.
- Instrumental methods: colorimetry uses Beer–Lambert (A = εcl); flame photometry detects Na, K, Li; chromatography separates by differential partitioning.
- Polymers: addition polymers form without a small molecule lost (polyethylene); condensation polymers lose water or HCl (nylon-6,6, PET).
- Fertilisers are graded by N:P:K percentages; urea (46% N) is the most concentrated common nitrogen fertiliser.
Worked example
A 1.00 g impure NaOH sample is dissolved and titrated against 0.500 M HCl; 20.0 mL is required. Find % purity.
Reasoning: moles HCl = 0.500 × 0.0200 = 0.0100 mol. NaOH + HCl is 1:1, so moles NaOH = 0.0100 mol. Mass = 0.0100 × 40 = 0.400 g. Percentage purity = (0.400/1.00) × 100 = 40.0%. The remaining 60% is inert impurity or absorbed water.
Traps
Using the acid's volume as if it were the sample volume; forgetting the 1:2 stoichiometry for H2SO4; choosing an indicator by habit rather than by the titration type; and reporting fertiliser N% without converting from NH3 or NO3 forms.