BSEH SS 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 packing) has 74 % packing efficiency, coordination number 12, four atoms per unit cell and r = a/(2√2).

Relative lowering of vapour pressure

For a non-volatile solute, Raoult's law gives (p° − p)/p° equal to the mole fraction of solute; it is a colligative property used to find molar mass.

van't Hoff factor

Symbol i is the ratio of the observed colligative property to the calculated value; i = 2 for fully dissociated NaCl and less than 1 for associating solutes such as benzoic acid.

Nernst equation at 298 K

E = E° − (0.0591/n) log Q, where n is the number of electrons transferred and Q the reaction quotient; it gives the potential at non-standard concentrations.

Molar conductivity

Λm = 1000κ/M with κ in S cm⁻¹ and M in mol L⁻¹; it increases on dilution, sharply for weak electrolytes because dissociation increases.

Faraday's first law of electrolysis

The mass deposited is proportional to the charge passed: m = (Q/F)(M/n) = ZIt, where F = 96500 C mol⁻¹ and Z is the electrochemical equivalent.

First order half-life

t½ = 0.693/k and is independent of initial concentration; after n half-lives the remaining concentration is [A]₀ divided by 2ⁿ.

Arrhenius equation

k = A e^(−Ea/RT) links the rate constant to temperature; a larger activation energy makes the rate far more sensitive to temperature change.

Order versus molecularity

Order is the experimental sum of concentration exponents in the rate law; molecularity is the theoretical number of species colliding in an elementary step and is never zero.

Freundlich adsorption isotherm

x/m = k·p^(1/n), so a plot of log(x/m) against log p is linear with slope 1/n between 0 and 1; it fails at high pressure.

Hardy-Schulze rule

The coagulating power of an ion increases with its charge, so for a negatively charged sol Al³⁺ > Ca²⁺ > Na⁺ in precipitating power.

Chemisorption versus physisorption

Chemisorption forms chemical bonds, releases 80–240 kJ mol⁻¹, is irreversible and monolayer; physisorption uses van der Waals forces, releases 20–40 kJ mol⁻¹ and is reversible and multilayer.

Calcination and roasting

Calcination heats a carbonate or hydrated ore in limited air, while roasting heats a sulphide ore in excess air to give the oxide and sulphur dioxide.

Zone refining

A metal rod is heated by a moving molten zone; impurities concentrate in the molten zone and are carried to one end, giving ultra-pure germanium and silicon.

Ellingham diagram

A plot of ΔG° for oxide formation against temperature; a metal whose line lies lower reduces the oxide above it, so carbon reduces ZnO above about 983 K.

Inert pair effect

The reluctance of the s² electron pair of heavier p-block elements (Tl, Pb, Bi) to take part in bonding makes the lower oxidation state, such as Pb²⁺, more stable.

Bleaching powder formation

Chlorine on dry slaked lime gives Ca(OCl)Cl: Ca(OH)₂ + Cl₂ → Ca(OCl)Cl + H₂O; dilute acid liberates chlorine from it.

Oxidising action of ozone

O₃ + 2H⁺ + 2e⁻ → O₂ + H₂O has E° = +2.07 V, so ozone oxidises iodide to iodine and sulphite to sulphate and bleaches by oxidation.

Spectrochemical series

Ligands ordered by field strength: I⁻ < Br⁻ < Cl⁻ < F⁻ < H₂O < NH₃ < en < NO₂⁻ < CN⁻ < CO; strong-field ligands give large Δo and low-spin complexes.

Spin-only magnetic moment

μ = √(n(n+2)) BM, where n is the number of unpaired electrons; high-spin Fe³⁺ with five unpaired electrons gives about 5.92 BM.

Tetrahedral crystal field splitting

Four ligands split the d orbitals so that Δt is about 4/9 of Δo and the e set lies lower than t2; tetrahedral complexes are almost always high spin.

Ionisation isomerism

Coordination compounds of the same formula that give different ions in solution, such as [Co(NH₃)₅Br]SO₄ and [Co(NH₃)₅SO₄]Br.

SN2 mechanism

A one-step bimolecular substitution with rate = k[substrate][nucleophile]; the nucleophile attacks opposite the leaving group and inverts the configuration.

Aryl halide inertness

The C–X bond of haloarenes has partial double-bond character from resonance and the carbon is sp² hybridised, so nucleophilic substitution needs extreme conditions.

Markownikoff's rule

In addition of HX to an unsymmetrical alkene, hydrogen goes to the carbon bearing more hydrogens; the peroxide effect reverses this only for HBr.

Lucas test

With anhydrous ZnCl₂ in concentrated HCl, tertiary alcohols turn cloudy immediately, secondary within about five minutes and primary only on heating.

Tollens' test

Ammoniacal silver nitrate gives a silver mirror with aldehydes but not with ketones; formic acid and α-hydroxy ketones also respond positively.

Clemmensen reduction

Zinc amalgam with concentrated HCl reduces aldehydes and ketones to hydrocarbons; acid-sensitive substrates are instead reduced by the Wolff–Kishner method using hydrazine and KOH.

Nucleophilic addition reactivity order

Aldehydes react faster than ketones: HCHO > CH₃CHO > other aldehydes > ketones, because alkyl groups donate electron density and sterically hinder the carbonyl carbon.

Hinsberg test

Benzenesulphonyl chloride distinguishes amines: a primary amine gives an alkali-soluble sulphonamide, a secondary an insoluble one and a tertiary none.

Reducing sugars

Sugars with a free aldehyde or ketone group reduce Tollens' and Fehling's reagents; sucrose is non-reducing because its glycosidic bond locks the anomeric carbon.

Bakelite

A thermosetting phenol-formaldehyde condensation polymer that is hard, heat resistant and used in electrical switches, plugs and utensil handles.