Assam ASSEB HS Chemistry flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Packing efficiency of FCC

FCC (cubic close-packed) has 74% packing efficiency; atoms per unit cell = 4; radius r = a/(2√2). SC 52.4%, BCC 68%.

van't Hoff factor i

i = observed colligative property / calculated value; equals number of particles per formula unit for strong electrolytes, less than expected due to ion pairing.

Raoult's law

For ideal solution, partial vapour pressure of each component = mole fraction × pure vapour pressure; total p = p°A xA + p°B xB.

Molar conductivity formula

Λm = κ × 1000 / M, where κ is conductivity in S cm^-1 and M is molarity in mol L^-1; it increases on dilution.

Kohlrausch law

Limiting molar conductivity of an electrolyte equals sum of limiting ionic conductivities times stoichiometric coefficients; used to find Λ° of weak electrolytes.

Nernst equation at 298 K

E = E° − (0.0591/n) log Q; for cell reaction, E_cell = E°_cell − (0.0591/n) log([products]/[reactants]).

First-order half-life

t1/2 = 0.693/k, independent of initial concentration; first-order integrated rate: ln[A] = ln[A]0 − kt, k in s^-1.

Arrhenius equation

k = A e^(−Ea/RT); ln(k2/k1) = (Ea/R)(1/T1 − 1/T2); plot ln k vs 1/T gives slope −Ea/R.

Order versus molecularity

Order is experimental sum of concentration exponents in rate law; molecularity is number of species colliding in an elementary step, always a small integer.

Tyndall effect

Scattering of light by colloidal particles, making the beam path visible; shown by colloids but not by true solutions.

Hardy-Schulze rule

Coagulating power of an ion increases with its charge; Al3+ > Ca2+ > Na+ for negatively charged colloid; opposite charge neutralises.

Roasting versus calcination

Roasting heats sulphide ore in excess air to oxide and SO2; calcination heats carbonate or hydroxide ore in limited air to oxide.

Inert pair effect

Reluctance of ns2 electrons to participate in bonding down p-block groups; makes lower oxidation state more stable, e.g., Pb2+ over Pb4+.

Lanthanoid contraction

Gradual decrease in atomic and ionic radii across lanthanoids due to poor shielding by 4f electrons; causes similarity of sizes and Y following.

KMnO4 in acidic medium

MnO4^- + 8H+ + 5e^- → Mn2+ + 4H2O; permanganate decolourises, acts as strong oxidising agent, n=5.

Chelate effect

Enhanced stability of complexes with polydentate ligands compared with similar monodentate ligands, due to favourable entropy change on complex formation.

Spectrochemical series

Order of ligand field strength: I^- < Br^- < Cl^- < F^- < H2O < NH3 < en < CN^- < CO; strong ligands cause large Δo and low spin.

EDTA denticity

EDTA is a hexadentate ligand: two nitrogen and four carboxylate oxygen donor atoms bind one metal ion, forming stable chelate complexes.

SN1 mechanism

Two-step nucleophilic substitution via carbocation; rate depends only on substrate; tertiary substrates react fastest and product is racemised.

Grignard reagent reaction with CO2

RMgX + CO2 → RCOO^- MgX+; acid work-up gives carboxylic acid with one more carbon than the alkyl halide.

Haloarene reactivity

Aryl halides resist nucleophilic substitution because C–X bond has partial double-bond character and sp2 carbon is less electrophilic; require drastic conditions.

Lucas test

Alcohol with ZnCl2/HCl: tertiary turns cloudy immediately, secondary in about five minutes, primary no turbidity at room temperature; distinguishes classes.

Reimer-Tiemann reaction

Phenol + CHCl3 + aqueous NaOH gives salicylaldehyde (2-hydroxybenzaldehyde) via dichlorocarbene; ortho-formylation of phenol.

Williamson synthesis

Ether preparation by SN2 reaction of sodium alkoxide with primary alkyl halide; tertiary halides favour elimination instead.

Cannizzaro reaction

Aldehydes lacking α-hydrogen, such as HCHO and benzaldehyde, undergo disproportionation with concentrated NaOH to give alcohol and carboxylate salt.

Tollens' test

Ammoniacal silver nitrate oxidises aldehydes to carboxylate, depositing silver mirror; ketones and most other groups do not respond.

Acidity of carboxylic acids

Carboxylic acids are more acidic than alcohols and phenols; electron-withdrawing groups stabilise carboxylate and increase acidity, e.g., ClCH2COOH > CH3COOH.

KMnO4 titration

In acidic medium KMnO4 oxidises oxalic acid or Mohr's salt; it is self-indicating, endpoint is faint pink, and n-factor is 5.

Hinsberg test

Reaction with benzenesulphonyl chloride distinguishes amines: primary gives soluble sulphonamide, secondary insoluble, tertiary no reaction.

Addition versus condensation polymer

Addition polymers form by chain growth of unsaturated monomers without by-product, e.g., polythene; condensation polymers form with loss of small molecules, e.g., nylon-6,6.

Soap micelle

Soap molecules aggregate in water with hydrophobic tails inward and ionic heads outward, solubilising grease; forms emulsion and cleans.

Primary standard

A highly pure, stable, non-hygroscopic substance used to standardise solutions, e.g., oxalic acid, potassium dichromate, sodium carbonate.