BSEB Intermediate Chemistry flashcards

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

Raoult's law

For a solution of volatile liquids, the partial vapour pressure of each component equals its mole fraction in the liquid multiplied by the vapour pressure of the pure component: p_A = p_A° x_A.

van't Hoff factor

Ratio of the observed colligative effect to the value expected for a non-dissociating solute. It exceeds 1 for electrolytes that split into ions and falls below 1 for solutes that associate.

Freezing point depression constant

K_f is the depression caused by a 1 molal solution; for water it is 1.86 K kg mol⁻¹. ΔT_f = i·K_f·m, so it depends on particle number, not identity.

Standard cell potential

E°_cell = E°_cathode − E°_anode using reduction potentials. A positive value means the cell reaction is spontaneous and ΔG° is negative, linked by ΔG° = −nFE°_cell.

Nernst equation

E = E° − (0.0591/n) log Q at 298 K. It corrects cell potential for non-standard concentrations; for a concentration cell E° is zero and E depends only on the ion concentration ratio.

Kohlrausch law

The limiting molar conductivity of an electrolyte equals the sum of the limiting ionic conductivities of its ions, each multiplied by its stoichiometric number: Λ°_m = ν₊λ°₊ + ν₋λ°₋.

First order half-life

For a first-order reaction t₁/₂ = 0.693/k, independent of initial concentration. The integrated form is ln([A]₀/[A]) = kt, giving a straight line for ln[A] against time.

Arrhenius equation

k = A e^(−E_a/RT). A plot of ln k against 1/T is linear with slope −E_a/R, so a steeper negative slope means a larger activation energy and stronger temperature dependence.

Pseudo-first-order reaction

A reaction that is second order overall but appears first order because one reactant, usually water, is in large excess so its concentration stays effectively constant, folding into the rate constant.

Spin-only magnetic moment

μ = √(n(n+2)) Bohr magnetons, where n is the number of unpaired electrons. It is used to deduce high-spin or low-spin configurations in transition metal complexes.

Lanthanoid contraction

The gradual decrease in atomic and ionic radii from lanthanum to lutetium, caused by poor shielding of the 4f electrons, which makes later lanthanoids smaller and chemically similar.

Disproportionation of MnO₄⁻

In acidic solution permanganate is reduced to Mn²⁺ (five electrons, E° = +1.51 V). In neutral or alkaline solution it gives brown MnO₂ instead, changing the observed colour and stoichiometry.

Crystal field splitting

Δ_o is the energy gap between the lower t₂g and upper e_g d orbitals in an octahedral field. Strong-field ligands give large Δ_o and low-spin complexes.

Spectrochemical series

Order of ligands by increasing field strength: I⁻ < Br⁻ < Cl⁻ < F⁻ < OH⁻ < H₂O < NH₃ < en < NO₂⁻ < CN⁻ < CO. Strong-field ligands favour low-spin complexes.

Linkage isomerism

Occurs when an ambidentate ligand such as NO₂⁻ or SCN⁻ can bond through either of two donor atoms, giving complexes with the same formula but different donor atoms attached to the metal.

SN2 mechanism

A one-step bimolecular substitution in which the nucleophile attacks the carbon from the side opposite the leaving group, giving inversion of configuration. Rate = k[substrate][nucleophile].

Finkelstein reaction

An alkyl chloride or bromide is heated with sodium iodide in dry acetone to give the alkyl iodide. Sodium bromide or chloride precipitates, shifting the equilibrium toward the product.

Aryl halide inertness

Aryl halides resist nucleophilic substitution because the carbon–halogen bond has partial double-bond character and the sp² carbon blocks backside attack by a nucleophile.

Lucas test

Conc. HCl with anhydrous ZnCl₂ is added to an alcohol. Tertiary alcohols turn cloudy at once, secondary within about five minutes, primary only on heating.

Williamson synthesis

An alkoxide reacts with a primary alkyl halide in an SN2 step to give an ether: RONa + R′X → R–O–R′ + NaX. Tertiary halides give elimination instead.

Reimer–Tiemann reaction

Phenol is treated with chloroform and aqueous sodium hydroxide, then acidified, to give salicylaldehyde. The formyl group enters mainly at the ortho position.

Tollens' test

Warm ammoniacal silver nitrate oxidises aldehydes to carboxylate, depositing a silver mirror. Ketones give no reaction, so it distinguishes aldehydes from ketones.

Cannizzaro reaction

Aldehydes lacking an α-hydrogen, such as benzaldehyde, disproportionate in concentrated alkali to give a carboxylate salt and the corresponding alcohol in equal amounts.

Iodoform test

Iodine with sodium hydroxide gives a yellow precipitate of CHI₃ for compounds containing a CH₃CO– group or a CH₃CH(OH)– group, such as acetone, acetaldehyde and ethanol.

Hofmann bromamide reaction

A primary amide is treated with bromine and potassium hydroxide to give a primary amine with one carbon fewer. It is used to prepare pure primary amines.

Hinsberg test

Benzenesulphonyl chloride reacts with primary amines to give a soluble sulphonamide, with secondary amines to give an insoluble one, and not at all with tertiary amines.

Diazonium salt coupling

Benzenediazonium chloride reacts with phenol in mildly alkaline solution to give an orange azo dye, an electrophilic substitution at the para position of the phenol ring.

Reducing and non-reducing sugars

Reducing sugars have a free anomeric carbon and reduce Tollens' and Fehling's reagents. Sucrose is non-reducing because both anomeric carbons are locked in the glycosidic bond.

Isoelectric point

The pH at which an amino acid carries equal positive and negative charges and exists mainly as a zwitterion, so it does not migrate in an electric field.

Xenon fluorides

Xenon forms XeF₂, XeF₄ and XeF₆ by direct reaction with fluorine under controlled conditions. Helium, neon and argon form essentially no stable compounds.

Brown ring test

Iron(II) sulphate is added to a nitrate solution, then concentrated sulphuric acid is poured down the tube side. A brown ring of FeSO₄·NO forms at the junction.

Chromyl chloride test

A chloride heated with potassium dichromate and concentrated sulphuric acid gives red chromium(VI) oxychloride vapour, which turns sodium hydroxide solution yellow with chromate.